Publications by year
In Press
Lybkær Kronborg Nielsen M, Ellis S, Towers JR, Doniol-Valcroze T, Franks DW, Cant M, Weiss M, Johnstone RA, Balcomb III KC, Ellifrit DK, et al (In Press). A long post-reproductive lifespan is a shared trait among genetically distinct killer whale populations.
Ecology and Evolution Full text.
Ozella L, Price E, Langford J, Lewis KE, Cattuto C, Croft D (In Press). Association networks and social temporal dynamics in ewes and lambs.
Applied Animal Behaviour Science Full text.
Dimitriadou S, Winberg S, Thörnqvist P-O, Croft DP, Darden SK (In Press). Brain monoaminergic activity during predator inspection in the Trinidadian guppy (Poecilia reticulata).
Abstract:
Brain monoaminergic activity during predator inspection in the Trinidadian guppy (Poecilia reticulata)
To understand the processes underpinning social decision-making, we need to determine how internal states respond to information gathered from the social environment. Brain monoamine neurotransmitters are key in the appraisal of the social environment and can reflect the internal state underlying behavioural responses to social stimuli. Here we determined the effects of conspecific partner cooperativeness during predator inspection on brain monoamine metabolic activity in Trinidadian guppies (Poecilia reticulata). We quantified the concentration of dopamine, serotonin and their metabolites across brain sections sampled immediately after ostensibly experiencing cooperation or defection from social partners whilst inspecting a predator model. Our results indicate dopaminergic and serotonergic activity differs with the cooperativeness experienced; these different neurotransmission profiles are likely to affect the expression and regulation of downstream behaviours that ultimately contribute to the patterning of cooperative interactions among individuals in the population.
Abstract.
Allen C, Croft D, Testard C, Brent L (In Press). Function of trunk-mediated “greeting” behaviours between male African elephants: insights from choice of partners.
Animals Full text.
Allen C, Croft DP, Brent LJN (In Press). Reduced older male presence linked to increased rates of aggression to non-conspecific targets in male elephants.
Proceedings of the Royal Society B: Biological Sciences Full text.
Yong L, Croft DP, Troscianko J, Ramnarine I, Wilson A (In Press). Sensory-based quantification of male colour patterns in Trinidadian guppies reveals nonparallel phenotypic evolution across an ecological transition in multivariate trait space.
Abstract:
Sensory-based quantification of male colour patterns in Trinidadian guppies reveals nonparallel phenotypic evolution across an ecological transition in multivariate trait space
ABSTRACTParallel evolution, in which independent populations evolve along similar phenotypic trajectories, offers insights into the repeatability of adaptive evolution. Here, we revisit a classic example of parallelism, that of repeated evolution of brighter males in the Trinidadian guppy. In guppies, colonisation of low predation habitats is associated with emergence of ‘more colourful’ phenotypes since predator-induced viability selection for crypsis weakens while sexual selection by female preference for conspicuity remains strong. Our study differs from previous investigations in three respects. First, we adopt a multivariate phenotyping approach to characterise parallelism in multi-trait space. Second, we use ecologically-relevant colour traits defined by the visual systems of the two selective agents (i.e. guppy, predatory cichlid). Third, we estimate population genetic structure to test for adaptive (parallel) evolution against a model of neutral phenotypyc divergence. We find strong phenotypic differentiation that is inconsistent with a neutral model, but only limited support for the predicted pattern of greater conspicuity at low predation. Effects of predation regime on each trait were in the expected direction, but weak, largely non-significant, and explained little among-population variation. In multi-trait space, phenotypic trajectories of lineages colonising low from high predation regimes were not parallel. Our results are consistent with reduced predation risk facilitating adaptive differentiation by female choice, but suggest that this proceeds in (effectively) independent directions of multi-trait space across lineages. Pool-sequencing data also revealed SNPs showing greater differentiation than expected under neutrality and/or associations with known colour genes in other species, presenting opportunities for future genetic study.
Abstract.
Dimitriadou S, Santos EM, Croft DP, van Aerle R, Ramnarine IW, Filby AL, Darden SK (In Press). Social partner cooperativeness influences brain oxytocin transcription in Trinidadian guppies (Poecilia reticulata).
Behavioural Brain ResearchAbstract:
Social partner cooperativeness influences brain oxytocin transcription in Trinidadian guppies (Poecilia reticulata)
AbstractFor non-kin cooperation to be maintained, individuals need to respond adaptively to the cooperative behaviour of their social partners. Currently, however, little is known about the biological responses of individuals to experiencing cooperation. Here, we quantify the neuroregulatory response of Trinidadian guppies (Poecilia reticulata) experiencing cooperation or defection by examining the transcriptional response of the oxytocin gene (oxt; also known as isotocin), which has been implicated in cooperative decision-making. We exposed wild-caught females to social environments where partners either cooperated or defected during predator inspection, or to a control (non-predator inspection) context, and quantified the relative transcription of the oxt gene. We tested an experimental group, originating from a site where individuals are under high predation threat and have previous experience of large aquatic predators (HP), and a control group, where individuals are under low predation threat and naïve to large aquatic predators (LP). In HP, but not LP, fish brain mid-section oxt relative transcription varied depending on social partner behaviour. HP fish experiencing cooperation during predator inspection had lower oxt transcription than those experiencing defection. This effect was not present in the control population or in the control context, where the behaviour of social partners did not affect oxt transcription. Our findings provide insight into the neuromodulation underpinning behavioural responses to social experiences, and ultimately to the proximate mechanisms underlying social decision-making.
Abstract.
Full text.
Grimes C, Brent L, Weiss M, Franks DW, Balcomb KC, Ellifrit DK, Ellis S, Croft D (In Press). The effect of age, sex, and resource abundance on patterns of rake markings in resident killer whales (Orcinus orca).
Marine Mammal Science Full text.
2021
Nielsen M, Ellis S, Towers J, Doniol-Valcroze T, Franks D, Cant M, Weiss M, Johnstone R, III KB, Ellifrit D, et al (2021). A long post-reproductive lifespan is a shared trait among genetically distinct killer whale populations.
Weiss MN, Franks DW, Giles DA, Youngstrom S, Wasser SK, Balcomb KC, Ellifrit DK, Domenici P, Cant MA, Ellis S, et al (2021). Age and sex influence social interactions, but not associations, within a killer whale pod.
Proceedings of the Royal Society B: Biological Sciences,
288(1953).
Abstract:
Age and sex influence social interactions, but not associations, within a killer whale pod
Social structure is a fundamental aspect of animal populations. In order to understand the function and evolution of animal societies, it is important to quantify how individual attributes, such as age and sex, shape social relationships. Detecting these influences in wild populations under natural conditions can be challenging, especially when social interactions are difficult to observe and broad-scale measures of association are used as a proxy. In this study, we use unoccupied aerial systems to observe association, synchronous surfacing, and physical contact within a pod of southern resident killer whales (Orcinus orca). We show that interactions do not occur randomly between associated individuals, and that interaction types are not interchangeable. While age and sex did not detectably influence association network structure, both interaction networks showed significant social homophily by age and sex, and centrality within the contact network was higher among females and young individuals. These results suggest killer whales exhibit interesting parallels in social bond formation and social life histories with primates and other terrestrial social mammals, and demonstrate how important patterns can be missed when using associations as a proxy for interactions in animal social network studies.
Abstract.
Full text.
Brask JB, Ellis S, Croft DP (2021). Animal social networks: an introduction for complex systems scientists.
Journal of Complex Networks,
9(2), 1-19.
Abstract:
Animal social networks: an introduction for complex systems scientists
Many animals live in societies where individuals frequently interact socially with each other. The social structures of these systems can be studied in depth by means of network analysis. A large number of studies on animal social networks in many species have in recent years been carried out in the biological research field of animal behaviour and have provided new insights into behaviour, ecology and social evolution. This line of research is currently not so well connected to the field of complex systems as could be expected. The purpose of this article is to provide an introduction to animal social networks for complex systems scientists and highlight areas of synergy. We believe that an increased integration of animal social networks with the interdisciplinary field of complex systems, and networks would be beneficial for various reasons. Increased collaboration between researchers in this field and biologists studying animal social systems could be valuable in solving challenges that are of importance to animal social network research. Furthermore, animal social networks provide the opportunity to investigate hypotheses about complex systems across a range of natural real-world social systems. In this article, we describe what animal social networks are and main research themes where they are studied; we give an overview of the methods commonly used to study animal social networks; we highlight challenges in the study of animal social networks where complex systems expertise may be particularly valuable; and we consider aspects of animal social networks that may be of particular interest to complex systems researchers. We hope that this will help to facilitate further interdisciplinary collaborations involving animal social networks and further integration of these networks into the field of complex systems.
Abstract.
Franks DW, Weiss MN, Silk MJ, Perryman RJY, Croft DP (2021). Calculating effect sizes in animal social network analysis.
Methods in Ecology and Evolution,
12(1), 33-41.
Abstract:
Calculating effect sizes in animal social network analysis
Because of the nature of social interaction or association data, when testing hypotheses using social network data it is common for network studies to rely on permutations to control for confounding variables, and to not also control for them in the fitted statistical model. This can be a problem because it does not adjust for any bias in effect sizes generated by these confounding effects, and thus the effect sizes are not informative in the presence of confounding variables. We implemented two network simulation examples and analysed an empirical dataset to demonstrate how relying solely on permutations to control for confounding variables can result in highly biased effect size estimates of animal social preferences that are uninformative when quantifying differences in behaviour. Using these simulations, we show that this can sometimes even lead to effect sizes that have the wrong sign and are thus the effect size is not biologically interpretable. We demonstrate how this problem can be addressed by controlling for confounding variables in the statistical dyadic or nodal model. We recommend this approach should be adopted as standard practice in the statistical analysis of animal social network data.
Abstract.
Full text.
Green PA, Preston EFR, Nicholl MH, Croft DP, Thompson FJ, Cant MA (2021). Collective defence and behavioural homogeneity during simulated territorial intrusions in banded mongooses (Mungos mungo).
ETHOLOGY,
127(10), 886-896.
Author URL.
Full text.
Weiss MN, Franks DW, Brent LJN, Ellis S, Silk MJ, Croft DP (2021). Common datastream permutations of animal social network data are not appropriate for hypothesis testing using regression models.
Methods in Ecology and Evolution,
12(2), 255-265.
Abstract:
Common datastream permutations of animal social network data are not appropriate for hypothesis testing using regression models
Social network methods have become a key tool for describing, modelling and testing hypotheses about the social structures of animals. However, due to the non-independence of network data and the presence of confounds, specialised statistical techniques are often needed to test hypotheses in these networks. Datastream permutations, originally developed to test the null hypothesis of random social structure, have become a popular tool for testing a wide array of null hypotheses in animal social networks. In particular, they have been used to test whether exogenous factors are related to network structure by interfacing these permutations with regression models. Here, we show that these datastream permutations typically do not represent the null hypothesis of interest to researchers interfacing animal social network analysis with regression modelling, and use simulations to demonstrate the potential pitfalls of using this methodology. Our simulations show that, if used to indicate whether a relationship exists between network structure and a covariate, datastream permutations can result in extremely high type I error rates, in some cases approaching 50%. In the same set of simulations, traditional node-label permutations produced appropriate type I error rates (~5%). Our analysis shows that datastream permutations do not represent the appropriate null hypothesis for these analyses. We suggest that potential alternatives to this procedure may be found in regarding the problems of non-independence of network data and unreliability of observations separately. If biases introduced during data collection can be corrected, either prior to model fitting or within the model itself, node-label permutations then serve as a useful test for interfacing animal social network analysis with regression modelling.
Abstract.
Full text.
Weiss MN, Ellis S, Croft DP (2021). Diversity and Consequences of Social Network Structure in Toothed Whales.
Frontiers in Marine Science,
8Abstract:
Diversity and Consequences of Social Network Structure in Toothed Whales
Toothed whales (suborder Odontoceti) are highly social, large brained mammals with diverse social systems. In recent decades, a large body of work has begun investigating these dynamic, complex societies using a common set of analytical tools: social network analysis. The application of social network theory to toothed whales enables insight into the factors that underlie variation in social structure in this taxon, and the consequences of these structures for survival, reproduction, disease transmission, and culture. Here, we perform a systematic review of the literature regarding toothed whale social networks to identify broad patterns of social network structure across species, common drivers of individual social position, and the consequences of network structure for individuals and populations. We also identify key knowledge gaps and areas ripe for future research. We recommend that future studies attempt to expand the taxonomic breadth and focus on standardizing methods and reporting as much as possible to allow for comparative analyses to test evolutionary hypotheses. Furthermore, social networks analysis may provide key insights into population dynamics as indicators of population health, predictors of disease risk, and as direct drivers of survival and reproduction.
Abstract.
Full text.
Allen CRB, Brent LJN, Motsentwa T, Croft DP (2021). Field evidence supporting monitoring of chemical information on pathways by male African elephants.
Animal Behaviour,
176, 193-206.
Abstract:
Field evidence supporting monitoring of chemical information on pathways by male African elephants
When animals move along well-established pathways, sensory cues along the path may provide valuable information concerning other individuals that have used the same route. Yet the extent to which animals use pathways as sources of public social information is poorly understood. Here we quantified the responses of wild African savannah elephants, Loxodonta africana, to olfactory information along natural elephant pathways, habitual routes that link predictable critical resources in the environment. By monitoring the behaviour of elephants travelling on pathways in a predominantly male study population, we found that elephants were highly olfactorily responsive to pathway substrate. Lone travellers were more responsive than elephants travelling in groups, suggesting elephants without social companions may be more dependent on olfactory cues on pathways during navigation. Furthermore, by experimentally presenting olfactory cues on pathways we found that male African elephants exhibited focused olfactory responses to urine cues of same-sex conspecifics for at least 48 h from time of deposition, and that urine from adult elephants was more likely to elicit vomeronasal system responses than subadult urine. African elephants may therefore potentially be able to discern the age and maturity of individuals they can expect to encounter in the environment from remote urine cues on pathways. We suggest elephant pathways act as a public information resource, assisting navigating elephants via the depositing of urine and dung by previous travellers on the route. These results could help inform elephant management, which may manipulate olfactory information on pathways in high human–wildlife conflict areas, or could use olfactory urine cues to improve the efficiency of corridors that link protected areas for elephants.
Abstract.
Full text.
Macario A, Darden SK, Verbruggen F, Croft DP (2021). Intraspecific variation in inhibitory motor control in guppies, Poecilia reticulata.
Journal of Fish Biology,
98(1), 317-328.
Abstract:
Intraspecific variation in inhibitory motor control in guppies, Poecilia reticulata
Inhibitory control (IC) is the ability to overcome impulsive or prepotent but ineffective responses in favour of more appropriate behaviours. The ability to inhibit internal predispositions or external temptations is vital in coping with a complex and variable world. Traditionally viewed as cognitively demanding and a main component of executive functioning and self-control, IC was historically examined in only a few species of birds and mammals but recently a number of studies has shown that a much wider range of taxa rely on IC. Furthermore, there is growing evidence that inhibitory abilities may vary within species at the population and individual levels owing to genetic and environmental factors. Here we use a detour-reaching task, a standard paradigm to measure motor inhibition in nonhuman animals, to quantify patterns of interindividual variation in IC in wild-descendant female guppies, Poecilia reticulata. We found that female guppies displayed inhibitory performances that were, on average, half as successful as the performances reported previously for other strains of guppies tested in similar experimental conditions. Moreover, we showed consistent individual variation in the ability to inhibit inappropriate behaviours. Our results contribute to the understanding of the evolution of fish cognition and suggest that IC may show considerable variation among populations within a species. Such variation in IC abilities might contribute to individual differences in other cognitive functions such as spatial learning, quantity discrimination or reversal learning.
Abstract.
Full text.
Croft DP, Weiss MN, Nielsen MLK, Grimes C, Cant MA, Ellis S, Franks DW, Johnstone RA (2021). Kinship dynamics: patterns and consequences of changes in local relatedness.
Proceedings of the Royal Society B: Biological Sciences,
288(1957), 20211129-20211129.
Abstract:
Kinship dynamics: patterns and consequences of changes in local relatedness
Mounting evidence suggests that patterns of local relatedness can change over time in predictable ways, a process termed kinship dynamics. Kinship dynamics may occur at the level of the population or social group, where the mean relatedness across all members of the population or group changes over time, or at the level of the individual, where an individual's relatedness to its local group changes with age. Kinship dynamics are likely to have fundamental consequences for the evolution of social behaviour and life history because they alter the inclusive fitness payoffs to actions taken at different points in time. For instance, growing evidence suggests that individual kinship dynamics have shaped the evolution of menopause and age-specific patterns of helping and harming. To date, however, the consequences of kinship dynamics for social evolution have not been widely explored. Here we review the patterns of kinship dynamics that can occur in natural populations and highlight how taking a kinship dynamics approach has yielded new insights into behaviour and life-history evolution. We discuss areas where analysing kinship dynamics could provide new insight into social evolution, and we outline some of the challenges in predicting and quantifying kinship dynamics in natural populations.
Abstract.
Full text.
Ellis S, Franks DW, Weiss MN, Cant MA, Domenici P, Balcomb KC, Ellifrit DK, Croft DP (2021). Mixture models as a method for comparative sociality: social networks and demographic change in resident killer whales.
Behavioral Ecology and Sociobiology,
75(4).
Abstract:
Mixture models as a method for comparative sociality: social networks and demographic change in resident killer whales
. Abstract
. In studies of social behaviour, social bonds are usually inferred from rates of interaction or association. This approach has revealed many important insights into the proximate formation and ultimate function of animal social structures. However, it remains challenging to compare social structure between systems or time-points because extrinsic factors, such as sampling methodology, can also influence the observed rate of association. As a consequence of these methodological challenges, it is difficult to analyse how patterns of social association change with demographic processes, such as the death of key social partners. Here we develop and illustrate the use of binomial mixture models to quantitatively compare patterns of social association between networks. We then use this method to investigate how patterns of social preferences in killer whales respond to demographic change. Resident killer whales are bisexually philopatric, and both sexes stay in close association with their mother in adulthood. We show that mothers and daughters show reduced social association after the birth of the daughter’s first offspring, but not after the birth of an offspring to the mother. We also show that whales whose mother is dead associate more with their opposite sex siblings and with their grandmother than whales whose mother is alive. Our work demonstrates the utility of using mixture models to compare social preferences between networks and between species. We also highlight other potential uses of this method such as to identify strong social bonds in animal populations.
.
. Significance statement
. Comparing patters of social associations between systems, or between the same systems at different times, is challenging due to the confounding effects of sampling and methodological differences. Here we present a method to allow social associations to be robustly classified and then compared between networks using binomial mixture models. We illustrate this method by showing how killer whales change their patterns of social association in response to the birth of calves and the death of their mother. We show that after the birth of her calf, females associate less with their mother. We also show that whales’ whose mother is dead associate more with their opposite sex siblings and grandmothers than whales’ whose mother is alive. This clearly demonstrates how this method can be used to examine fine scale temporal processes in animal social systems.
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Abstract.
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Preston EFR, Thompson FJ, Ellis S, Kyambulima S, Croft DP, Cant MA (2021). Network-level consequences of outgroup threats in banded mongooses: Grooming and aggression between the sexes.
Journal of Animal Ecology,
90(1), 153-167.
Abstract:
Network-level consequences of outgroup threats in banded mongooses: Grooming and aggression between the sexes
Animal groups are heterogeneous assemblages of individuals with differing fitness interests, which may lead to internal conflict over investment in group territorial defence. Differences between individuals may lead to different behavioural responses to intergroup conflict, particularly between the sexes. These potential impacts have been little studied. We used social network analysis to investigate the impact of simulated intergroup conflicts on social relationships in groups of wild banded mongooses Mungos mungo, in which intergroup fights are more costly for males than females. We predicted that social cohesion (specifically male-to-male and female-to-male grooming) would increase after conflict, and aggression would decrease, to minimize conflict between the sexes. Simulated intergroup conflicts were performed by exposing banded mongoose groups to scents, ‘war cry’ playbacks, and live intruders from a rival group. All grooming and aggression interactions between individuals were recorded, and grooming and aggression social networks were created for the 2 days preceding a simulated intergroup conflict (pre-conflict network) and the 2 days after (post-conflict network). We found no evidence of an increase in social cohesion after simulated conflicts, measured as grooming eigenvector centrality. Male-to-male, male-to-female and female-to-male grooming strength decreased after simulated intrusions compared to female-to-female grooming strength. However, male–female aggression decreased in intrusion trials compared to other interaction types, consistent with the hypothesis that intergroup encounters reduce the level of intragroup conflict between males and females. Males were more affected socially by intergroup encounters than females, which may be because they are investing in defence rather than internal relationships. Focusing on individual relationship changes, using social network analysis, can reveal changes in the directionality of behaviour in response to intergroup encounters, and highlight how individual responses to conflict may scale up to affect social networks and, potentially, group performance. This study highlights the importance of studying both group-level behaviours and individual relationships to more fully understand responses to intergroup encounters.
Abstract.
Full text.
Yong L, Croft DP, Troscianko J, Ramnarine IW, Wilson AJ (2021). Sensory-based quantification of male colour patterns in Trinidadian guppies reveals no support for parallel phenotypic evolution in multivariate trait space.
Mol EcolAbstract:
Sensory-based quantification of male colour patterns in Trinidadian guppies reveals no support for parallel phenotypic evolution in multivariate trait space.
Parallel evolution, in which independent populations evolve along similar phenotypic trajectories, offers insights into the repeatability of adaptive evolution. Here, we revisit a classic example of parallelism, that of repeated evolution of brighter males in the Trinidadian guppy (Poecilia reticulata). In guppies, colonisation of low predation habitats is associated with emergence of 'more colourful' phenotypes since predator-induced viability selection for crypsis weakens while sexual selection by female preference for conspicuousness remains strong. Our study differs from previous investigations in three respects. First, we adopted a multivariate phenotyping approach to characterise parallelism in multitrait space. Second, we used ecologically-relevant colour traits defined by the visual systems of the two selective agents (i.e. guppy, predatory cichlid). Third, we estimated population genetic structure to test for adaptive (parallel) evolution against a model of neutral phenotypic divergence. We find strong phenotypic differentiation that is inconsistent with a neutral model but very limited support for the predicted pattern of greater conspicuousness at low predation. Effects of predation regime on each trait were in the expected direction, but weak, largely nonsignificant, and explained little among-population variation. In multitrait space, phenotypic trajectories of lineages colonising low from high predation regimes were not parallel. Our results are consistent with reduced predation risk facilitating adaptive differentiation, potentially by female choice, but suggest that this proceeds in independent directions of multitrait space across lineages. Pool-sequencing data also revealed SNPs showing greater differentiation than expected under neutrality, among which some are found in genes contributing to colour pattern variation, presenting opportunities for future genetic study.
Abstract.
Author URL.
Preston EFR, Thompson FJ, Kyabulima S, Croft DP, Cant MA (2021). The dynamics of social cohesion in response to simulated intergroup conflict in banded mongooses.
ECOLOGY AND EVOLUTION,
11(24), 18662-18675.
Author URL.
2020
Heathcote RJP, Troscianko J, Darden S, Naisbett-Jones LC, Laker P, Brown AM, Ramnarine IW, Walker J, Croft D (2020). A matador-like predator diversion strategy driven by conspicuous colouration in guppies.
Current Biology,
30 (14), 2844-2851.
Full text.
Brask JB, Ellis S, Croft DP (2020). Animal social networks: an introduction for complex systems scientists.
Franks DW, Weiss MN, Silk MJ, Perryman RJY, Croft DP (2020). Calculating effect sizes in animal social network analysis.
Weiss MN, Franks DW, Brent LJN, Ellis S, Silk MJ, Croft DP (2020). Common datastream permutations of animal social network data are not appropriate for hypothesis testing using regression models.
Rose PE, Croft DP (2020). Evaluating the social networks of four flocks of captive flamingos over a five-year period: Temporal, environmental, group and health influences on assortment.
Behavioural Processes,
175Abstract:
Evaluating the social networks of four flocks of captive flamingos over a five-year period: Temporal, environmental, group and health influences on assortment
Flamingos are well known for their gregarious habits and aggregations in large flocks, but evaluation of the mechanisms behind social grouping remain poorly understood. Captive birds provide a useful model for investigating aspects of social choice in highly gregarious, long-lived species. Animals invest in social relationships that convey fitness benefits and bonds can be long-lasting. For some species, field-based measurement of social networks can be difficult. Captive populations therefore provide a useful alternative for measuring social choices. Data were collected on flamingos at WWT Slimbridge Wetland Centre from 2013 to 2016 and compared to data from 2012. For three flocks, associations were analysed along with individual foot health scores to identify any relationship between health and social behaviour. Long-term partnerships were present in all flocks; preferred associates noted in 2012 were present in 2016. Matrix correlations across years were positive; arrangements of dyads, trios and quartets with higher ties strengths were visible at the beginning and end of the study. Both male-male and female-female bonds were stable over time. All flamingos were more frequently seen socialising than solitary; those in the largest flock showed the highest occurrence of social behaviour (irrespective of enclosure size differences). The number of connections realised from all available within a network was significantly influenced by season. Foot health did not predict associations in these three flamingo networks. Our results indicate that flamingo societies are complex (i.e. formed of long-standing preferential partnerships and not loose, random connections) and the impact of flock size and environment on sociality should be investigated further. These results are helpful for those working with captive flamingos to consider the number of birds housed so that an array of opportunities for choice of associate and/or breeding partner are available in zoo-housed flocks.
Abstract.
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Allen CRB, Brent LJN, Motsentwa T, Weiss MN, Croft DP (2020). Importance of old bulls: leaders and followers in collective movements of all-male groups in African savannah elephants (Loxodonta africana).
Scientific Reports,
10(1).
Abstract:
Importance of old bulls: leaders and followers in collective movements of all-male groups in African savannah elephants (Loxodonta africana)
AbstractIn long-lived social species, older individuals can provide fitness benefits to their groupmates through the imparting of ecological knowledge. Research in this area has largely focused on females in matrilineal societies where, for example, older female African savannah elephants (Loxodonta africana) are most effective at making decisions crucial to herd survival, and old post-reproductive female resident killer whales (Orcinus orca) lead collective movements in hunting grounds. In contrast, little is known about the role of older males as leaders in long-lived social species. By analysing leadership patterns of all-male African savannah elephant traveling groups along elephant pathways in Makgadikgadi Pans National Park, Botswana, we found that the oldest males were more likely to lead collective movements. Our results challenge the assumption that older male elephants are redundant in the population and raise concerns over the biased removal of old bulls that currently occurs in both legal trophy hunting and illegal poaching. Selective harvesting of older males could have detrimental effects on the wider elephant society through loss of leaders crucial to younger male navigation in unknown, risky environments.
Abstract.
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Weiss MN, Franks DW, Balcomb KC, Ellifrit DK, Silk MJ, Cant MA, Croft DP (2020). Modelling cetacean morbillivirus outbreaks in an endangered killer whale population.
Biological Conservation,
242Abstract:
Modelling cetacean morbillivirus outbreaks in an endangered killer whale population
The emergence of novel diseases represents a major hurdle for the recovery of endangered populations, and in some cases may even present the threat of extinction. In recent years, epizootics of infectious diseases have emerged as a major threat to marine mammal populations, particularly group-living odontocetes. However, little research has explored the potential consequences of novel pathogens in endangered cetacean populations. Here, we present the first study predicting the spread of infectious disease over the social network of an entire free-ranging cetacean population, the southern resident killer whale community (SRKW). Utilizing 5 years of detailed data on close contacts between individuals, we build a fine-scale social network describing potential transmission pathways in this population. We then simulate the spread of cetacean morbillivirus (CeMV) over this network. Our analysis suggests that the SRKW population is highly vulnerable to CeMV. The majority of simulations resulted in unusual mortality events (UMEs), with mortality rates predicted to be at least twice the recorded maximum annual mortality. We find only limited evidence that this population's social structure inhibits disease spread. Vaccination is not likely to be an efficient strategy for reducing the likelihood of UMEs, with over 40 vaccinated individuals (>50% of the population) required to reduce the likelihood of UMEs below 5%. This analysis highlights the importance of modelling efforts in designing strategies to mitigate disease, and suggests that populations with strong social preferences and distinct social units may still be highly vulnerable to disease outbreaks.
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Chopra K, Hodges HR, Barker ZE, Vazquez Diosdado JA, Amory JR, Cameron TC, Croft DP, Bell NJ, Codling EA (2020). Proximity Interactions in a Permanently Housed Dairy Herd: Network Structure, Consistency, and Individual Differences.
FRONTIERS IN VETERINARY SCIENCE,
7 Author URL.
Ozella L, Langford J, Gauvin L, Price E, Cattuto C, Croft DP (2020). The effect of age, environment and management on social contact patterns in sheep.
APPLIED ANIMAL BEHAVIOUR SCIENCE,
225 Author URL.
Full text.
Darden SK, James R, Cave JM, Brask JB, Croft DP (2020). Trinidadian guppies use a social heuristic that can support cooperation among non-kin.
Proceedings. Biological sciences,
287(1934).
Abstract:
Trinidadian guppies use a social heuristic that can support cooperation among non-kin
Cooperation among non-kin is well documented in humans and widespread in non-human animals, but explaining the occurrence of cooperation in the absence of inclusive fitness benefits has proven a significant challenge. Current theoretical explanations converge on a single point: cooperators can prevail when they cluster in social space. However, we know very little about the real-world mechanisms that drive such clustering, particularly in systems where cognitive limitations make it unlikely that mechanisms such as score keeping and reputation are at play. Here, we show that Trinidadian guppies (Poecilia reticulata) use a 'walk away' strategy, a simple social heuristic by which assortment by cooperativeness can come about among mobile agents. Guppies cooperate during predator inspection and we found that when experiencing defection in this context, individuals prefer to move to a new social environment, despite having no prior information about this new social group. Our results provide evidence in non-human animals that individuals use a simple social partner updating strategy in response to defection, supporting theoretical work applying heuristics to understanding the proximate mechanisms underpinning the evolution of cooperation among non-kin.
Abstract.
Full text.
2019
Dimitriadou S, Croft DP, Darden SK (2019). Divergence in social traits in Trinidadian guppies selectively bred for high and low leadership in a cooperative context.
Scientific Reports,
9(1).
Abstract:
Divergence in social traits in Trinidadian guppies selectively bred for high and low leadership in a cooperative context
In many animal species, individuals with certain morphological, physiological, or behavioural traits may have a disproportionately large role in determining group behaviour. While most empirical studies of leadership have focused on behaviour of individuals exploring new environments or foraging, little is known about leading behaviour in other ecological contexts. Here, we use a selective breeding design in the Trinidadian guppy (Poecilia reticulata) to quantify the heritability of leadership in a cooperative context, and determine the behavioural traits associated with it. Firstly we found that phenotypic selection for high and low leadership (HL and LL, respectively) over three filial generations resulted in pronounced differences in leadership tendency with a moderate degree of heritability. In our assay of other social traits, LL males were more aggressive and sampled their social environment less than HL males, but HL and LL females did not differ in either aggressiveness or sociability. Traits such as boldness and exploratory tendency did not diverge between the two lines. Leading behaviour was thus associated with social traits in males, but not females; suggesting that there may be sex-specific mechanisms driving the emergence of leadership in this context. We discuss our findings in the context of the evolution of cooperation.
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Brask JB, Croft DP, Edenbrow M, James R, Bleakley BH, Ramnarine IW, Heathcote RJP, Tyler CR, Hamilton PB, Dabelsteen T, et al (2019). Evolution of non-kin cooperation: social assortment by cooperative phenotype in guppies.
R Soc Open Sci,
6(1).
Abstract:
Evolution of non-kin cooperation: social assortment by cooperative phenotype in guppies.
Cooperation among non-kin constitutes a conundrum for evolutionary biology. Theory suggests that non-kin cooperation can evolve if individuals differ consistently in their cooperative phenotypes and assort socially by these, such that cooperative individuals interact predominantly with one another. However, our knowledge of the role of cooperative phenotypes in the social structuring of real-world animal populations is minimal. In this study, we investigated cooperative phenotypes and their link to social structure in wild Trinidadian guppies (Poecilia reticulata). We first investigated whether wild guppies are repeatable in their individual levels of cooperativeness (i.e. have cooperative phenotypes) and found evidence for this in seven out of eight populations, a result which was mostly driven by females. We then examined the social network structure of one of these populations where the expected fitness impact of cooperative contexts is relatively high, and found assortment by cooperativeness, but not by genetic relatedness. By contrast, and in accordance with our expectations, we did not find assortment by cooperativeness in a population where the expected fitness impact of cooperative contexts is lower. Our results provide empirical support for current theory and suggest that assortment by cooperativeness is important for the evolution and persistence of non-kin cooperation in real-world populations.
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Cant MA, Croft DP (2019). Grandmothering in space and time.
Current Biology Full text.
Silk MJ, Hodgson DJ, Rozins C, Croft DP, Delahay RJ, Boots M, McDonald RA (2019). Integrating social behaviour, demography and disease dynamics in network models: Applications to disease management in eclining wildlife populations.
Philosophical Transactions of the Royal Society B: Biological Sciences,
374(1781).
Abstract:
Integrating social behaviour, demography and disease dynamics in network models: Applications to disease management in eclining wildlife populations
The emergence and spread of infections can contribute to the decline and extinction of populations, particularly in conjunction with anthropogenic environmental change. The importance of heterogeneity in processes of transmission, resistance and tolerance is increasinglywell understood in theory, but empirical studies that consider both the demographic and behavioural implications of infection are scarce. Non-random mixing of host individuals can impact the demographic thresholds that determine the amplification or attenuation of disease prevalence. Risk assessment and management of disease in threatened wildlife populations must therefore consider not just host density, but also the social structure of host populations. Here we integrate the most recent developments in epidemiological research from a demographic and social network perspective, and synthesize the latest developments in social network modelling for wildlife disease, to explore their applications to disease management in populations in decline and at risk of extinction.We use simulated examples to support our key points and reveal howdisease-management strategies can and should exploit both behavioural and demographic information to prevent or control the spread of disease. Our synthesis highlights the importance of considering the combined impacts of demographic and behavioural processes in epidemics to successful disease management in a conservation context. This article is part of the theme issue 'Linking behaviour to dynamics of populations and communities: application of novel approaches in behavioural ecology to conservation'.
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Macario A, Croft DP, Darden SK (2019). Male phenotypic diversity experienced during ontogeny mediates female mate choice in guppies.
Behavioral Ecology,
30(2), 465-473.
Abstract:
Male phenotypic diversity experienced during ontogeny mediates female mate choice in guppies
Early social experience can be important in shaping female mate choice. Previous work has shown that females adjust their decisions based on the distribution of male sexual trait values encountered during development. However, other phenotypic features could be important in the formation of mate preferences if, for example, they provide additional information about the males available. Here, we examined how the level of overall phenotypic variance (independent of trait values) experienced during ontogeny, mediated female choice in guppies, Poecilia reticulata. Developing females were reared with males either all different in coloration or all similar in coloration or with adult females representing high variance, low variance, and no experience of male variance, respectively. We found that females were more sexually responsive when reared with females only than in either of the male treatments. When reared with males, responsiveness was greater in the low-variance treatment compared with the high-variance treatment. Moreover, females had stronger sexual preferences after rearing in the high-variance condition compared with the low-variance condition. In turn, males switched mating tactics, increasing the rate of coerced copulation attempts when facing choosier females, possibly to balance the loss in mating opportunities. Taken together, these results demonstrate the adaptive plasticity of female mating decisions and the dynamic selection pressures they might impose on the evolution of male sexual traits, potentially contributing to the maintenance of the extreme polymorphism found in male color patterns.
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Weiss MN, Franks DW, Croft DP, Whitehead H (2019). Measuring the complexity of social associations using mixture models.
BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY,
73(1).
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Nattrass S, Croft DP, Ellis S, Cant MA, Weiss MN, Wright BM, Stredulinsky E, Doniol-Valcroze T, Ford JKB, Balcomb KC, et al (2019). Postreproductive killer whale grandmothers improve the survival of their grandoffspring.
Proceedings of the National Academy of Sciences of the United States of America,
116(52), 26669-26673.
Abstract:
Postreproductive killer whale grandmothers improve the survival of their grandoffspring
Understanding why females of some mammalian species cease ovulation prior to the end of life is a long-standing interdisciplinary and evolutionary challenge. In humans and some species of toothed whales, females can live for decades after stopping reproduction. This unusual life history trait is thought to have evolved, in part, due to the inclusive fitness benefits that postreproductive females gain by helping kin. In humans, grandmothers gain inclusive fitness benefits by increasing their number of surviving grandoffspring, referred to as the grandmother effect. Among toothed whales, the grandmother effect has not been rigorously tested. Here, we test for the grandmother effect in killer whales, by quantifying grandoffspring survival with living or recently deceased reproductive and postreproductive grandmothers, and show that postreproductive grandmothers provide significant survival benefits to their grandoffspring above that provided by reproductive grandmothers. This provides evidence of the grandmother effect in a nonhuman menopausal species. By stopping reproduction, grandmothers avoid reproductive conflict with their daughters, and offer increased benefits to their grandoffspring. The benefits postreproductive grandmothers provide to their grandoffspring are shown to be most important in difficult times where the salmon abundance is low to moderate. The postreproductive grandmother effect we report, together with the known costs of late-life reproduction in killer whales, can help explain the long postreproductive life spans of resident killer whales.
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2018
Ellis S, Franks DW, Nattrass S, Currie TE, Cant MA, Giles D, Balcomb KC, Croft DP (2018). Analyses of ovarian activity reveal repeated evolution of post-reproductive lifespans in toothed whales.
SCIENTIFIC REPORTS,
8 Author URL.
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Silk MJ, Weber NL, Steward LC, Hodgson DJ, Boots M, Croft DP, Delahay RJ, McDonald RA (2018). Contact networks structured by sex underpin sex-specific epidemiology of infection.
Ecology Letters,
21(2), 309-318.
Abstract:
Contact networks structured by sex underpin sex-specific epidemiology of infection
Contact networks are fundamental to the transmission of infection and host sex often affects the acquisition and progression of infection. However, the epidemiological impacts of sex-related variation in animal contact networks have rarely been investigated. We test the hypothesis that sex-biases in infection are related to variation in multilayer contact networks structured by sex in a population of European badgers Meles meles naturally infected with Mycobacterium bovis. Our key results are that male-male and between-sex networks are structured at broader spatial scales than female-female networks and that in male-male and between-sex contact networks, but not female-female networks, there is a significant relationship between infection and contacts with individuals in other groups. These sex differences in social behaviour may underpin male-biased acquisition of infection and may result in males being responsible for more between-group transmission. This highlights the importance of sex-related variation in host behaviour when managing animal diseases.
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Heathcote RJP, Darden SK, Troscianko J, Lawson MRM, Brown AM, Laker PR, Naisbett-Jones LC, MacGregor HEA, Ramnarine I, Croft DP, et al (2018). Dynamic eye colour as an honest signal of aggression.
Current Biology,
28(11), R652-R653.
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Rose PE, Brereton JE, Croft DP (2018). Measuring welfare in captive flamingos: Activity patterns and exhibit usage in zoo-housed birds.
Applied Animal Behaviour Science,
205, 115-125.
Abstract:
Measuring welfare in captive flamingos: Activity patterns and exhibit usage in zoo-housed birds
Birds do not always feature heavily in zoo-based welfare and behaviour research. Studying how individuals use the space provided to them helps inform captive care and enables objective measurement of animal welfare. The aim of this study was to determine the variables that influence how flamingos use their zoo enclosures. By observing changes in enclosure use and behaviour over a long-term period, we aimed to assess the influences of variables outside of the bird's control. Five flocks of captive flamingos (Caribbean, Chilean, Andean, greater and lesser) at WWT Slimbridge Wetland Centre were used in this research. Data were collected from Spring/Summer 2012 to Summer 2016, with a modified Spread of Participation Index being used to evaluate space use. Data on state behaviours including foraging, preening, and loafing were collected to assess time-activity budgets and to calculate population-level behavioural diversity. Climate data and visitor number were also recorded. Results show similarities between the patterns of diurnal activity of these flamingos and that published on wild birds, with higher levels of activity occurring later in the day. SPI values show that each flock had a preferred area of occupancy within their enclosure, but all flocks also showed variation in space use, suggesting that these large enclosure sizes allow individual birds choice over where to perform different behaviours. Both season and time of day influenced when flamingos were most likely to be active, as well as when they would use the widest range of enclosure areas. There was no visitor effect, based on no reduction in enclosure usage or change in activity patterns of birds when experiencing higher visitor numbers. Our results demonstrate that it is possible to measure flock-wide behaviour in large groups of birds, and that these data are useful in explaining how animals behave across years and seasons. We encourage more research into the activity patterns of captive flamingos, especially in flocks that may be reluctant to breed, to provide more information on flock-wide responses to a human-created environment.
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Rose PE, Lloyd I, Brereton JE, Croft DP (2018). Patterns of nocturnal activity in captive greater flamingos.
Zoo Biology,
37(5), 290-299.
Abstract:
Patterns of nocturnal activity in captive greater flamingos
Wild flamingos are known to forage overnight, but little is known of their nocturnal activity patterns in captivity. Captive flamingos can show daytime inactivity, reflecting natural periods of resting and loafing documented in wild birds. Assessment of behavior outside of normal zoo opening hours can provide more detailed information on how animals use the space provided to them, and highlights how enclosure areas not commonly occupied during the day may still be important for inhabitants at other times. We examine whether captive flamingos at WWT Slimbridge Wetland Centre change their enclosure usage and behavior overnight compared to that observed during daylight. Using three night-vision remote cameras, the behavior and enclosure usage of a flock of over 270 greater flamingos was recorded from March to July 2016. Results show that these flamingos had higher rates of foraging at certain points during the night, and had a more even enclosure usage when compared to daylight hours. Change in pool use is apparent throughout the course of the day and night, suggesting that different areas of water depth are used by these flamingos at different times. Flamingos increased nocturnal foraging in their pool during the breeding season. The large enclosure size and range of different land and water areas may have enabled these flamingos to follow daily activity patterns similar to those observed in wild birds. Captive flamingos clearly show a difference between daytime and nocturnal behavior patterns and this should be considered when designing enclosures and general management routines for these birds.
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Pavelka MSM, Brent LJN, Croft DP, Fedigan LM (2018). Post-fertile Lifespan in Female Primates and Cetaceans. In Kalbitzer U, Jack K (Eds.)
Primate Life Histories, Sex Roles, and Adaptability. Developments in Primatology: Progress and Prospects, Springer, Cham.
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Ellis S, Franks DW, Nattrass S, Cant MA, Bradley DL, Giles D, Balcomb KC, Croft DP (2018). Postreproductive lifespans are rare in mammals.
Ecology and Evolution,
8(5), 2482-2494.
Abstract:
Postreproductive lifespans are rare in mammals
A species has a post-reproductive stage if, like humans, a female entering the adult population can expect to live a substantial proportion of their life after their last reproductive event. However, it is conceptually and statistically challenging to distinguish these true post-reproductive stages from the usual processes of senescence, which can result in females occasionally surviving past their last reproductive event. Hence, despite considerable interest, the taxonomic prevalence of post-reproductive stages remains unclear and debated. In this study we use life tables constructed from published data on wild populations of mammals, and statistical measures of post-reproductive lifespans, to distinguish true post-reproductive stages from artefacts of senescence and demography in 52 species. We find post-reproductive stages are rare in mammals and are limited to humans and a few species of toothed whales. By resolving this long-standing debate, we hope to provide clarity for researchers in the field of evolutionary biology and a solid foundation for further studies investigating the evolution and adaptive significance of this unusual life history trait.
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Silk MJ, Drewe JA, Delahay RJ, Weber N, Steward LC, Wilson-Aggarwal J, Boots M, Hodgson DJ, Croft DP, McDonald RA, et al (2018). Quantifying direct and indirect contacts for the potential transmission of infection between species using a multilayer contact network.
Behaviour,
155(7-9), 731-757.
Abstract:
Quantifying direct and indirect contacts for the potential transmission of infection between species using a multilayer contact network
Detecting opportunities for between-species transmission of pathogens can be challenging, particularly if rare behaviours or environmental transmission are involved. We present a multilayer network framework to quantify transmission potential in multi-host systems, incorporating environmental transmission, by using empirical data on direct and indirect contacts between European badgers Meles meles and domestic cattle. We identify that indirect contacts via the environment at badger latrines on pasture are likely to be important for transmission within badger populations and between badgers and cattle. We also find a positive correlation between the role of individual badgers within the badger social network, and their role in the overall badger-cattle-environment network, suggesting that the same behavioural traits contribute to the role of individual badgers in within- and between-species transmission. These findings have implications for disease management interventions in this system, and our novel network approach can provide general insights into transmission in other multi-host disease systems.
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Rose PE, Croft DP (2018). Quantifying the social structure of a large captive flock of greater flamingos (Phoenicopterus roseus): Potential implications for management in captivity.
Behavioural Processes,
150, 66-74.
Abstract:
Quantifying the social structure of a large captive flock of greater flamingos (Phoenicopterus roseus): Potential implications for management in captivity
An appropriate social environment for species held in captivity is key for ensuring both good welfare and reproductive performance. Species with a complex social structure may suffer if their social requirements are not taken into consideration as part of management and husbandry strategies. Here we aim to understand the drivers of social structure, and the link between social structure and reproduction in a flock of 281 greater flamingos (Phoenicopterus roseus) at WWT Slimbridge Wetland Centre. Proximity-based associations between birds were measured three and four times per day (depending upon season and husbandry) from 2012 to 2016. To determine the effect of reproductive activity on social structure, display and nesting behaviour were also recorded for the 2015 breeding season (April–July). Results showed that birds displayed a wider range of social relationships, and that affiliations within the flock were not random. This flamingo flock was differentiated into discrete subgroups, and social structure was stable across some years, but not over all seasons. Social bonds were more consistent across seasons into the nesting period rather than outside of it. During breeding, not all birds that displayed built a nest, and not all displaying birds nested. Future research should further investigate differences in display and nesting patterns within a flock, and determine how the social structure of large flocks compares to smaller flocks of this species. Comparing captive data to information on wild bird sociality would be relevant to highlight any differences in patterns of assortment and connectivity.
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Rozins C, Silk MJ, Croft DP, Delahay RJ, Hodgson DJ, McDonald RA, Weber N, Boots M (2018). Social structure contains epidemics and regulates individual roles in disease transmission in a group-living mammal.
Ecology and Evolution,
8(23), 12044-12055.
Abstract:
Social structure contains epidemics and regulates individual roles in disease transmission in a group-living mammal
Population structure is critical to infectious disease transmission. As a result, theoretical and empirical contact network models of infectious disease spread are increasingly providing valuable insights into wildlife epidemiology. Analyzing an exceptionally detailed dataset on contact structure within a high-density population of European badgers Meles meles, we show that a modular contact network produced by spatially structured stable social groups, lead to smaller epidemics, particularly for infections with intermediate transmissibility. The key advance is that we identify considerable variation among individuals in their role in disease spread, with these new insights made possible by the detail in the badger dataset. Furthermore, the important impacts on epidemiology are found even though the modularity of the Badger network is much lower than the threshold that previous work suggested was necessary. These findings reveal the importance of stable social group structure for disease dynamics with important management implications for socially structured populations.
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Diosdado JAV, Barker ZE, Hodges HR, Amory JR, Croft DP, Bell NJ, Codling EA (2018). Space-use patterns highlight behavioural differences linked to lameness, parity, and days in milk in barn-housed dairy cows.
PLOS ONE,
13(12).
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Barker ZE, Diosdado JAV, Codling EA, Bell NJ, Hodges HR, Croft DP, Amory JR (2018). Use of novel sensors combining local positioning and acceleration to measure feeding behavior differences associated with lameness in dairy cattle.
JOURNAL OF DAIRY SCIENCE,
101(7), 6310-6321.
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2017
Macario A, Croft DP, Endler JA, Darden SK (2017). Early social experience shapes female mate choice in guppies.
Behavioral Ecology,
28(3), 833-843.
Abstract:
Early social experience shapes female mate choice in guppies
Mating decisions are often plastic and individuals adjust their decisions depending on the social and ecological environment. Although the implications of the social environment on mate choice has been well studied in species with parental care, surprisingly little research has examined the role played by the social environment experienced during ontogeny in species lacking parental care. We used guppies to test the hypothesis that females alter their mate choice in response to variation in the distribution of male sexual traits encountered during development. To manipulate their juvenile experience, we exposed maturing females to groups of males differing in the values of male coloration, known to be sexual traits in guppies. These exposures were carried out either during the entire developmental period or the latter half of the developmental period. Both choosiness and preference functions for a number of male color traits were affected by rearing treatments. Furthermore, females exhibited disassortative preferences for the phenotypes experienced as juveniles, suggesting a rare-male advantage. Finally, depending on male stimuli, only long-exposed females formed preferences for specific male colors. Our study demonstrates the importance of socially mediated preferences and highlights how preferences for rare phenotypes and fluctuating selection due to heterogeneity in signaling conditions may contribute to the maintenance of the polymorphism found in male color patterns.
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Lacy RC, Williams R, Ashe E, III BKC, Brent LJN, Clark CW, Croft DP, Giles DA, MacDuffee M, Paquet PC, et al (2017). Evaluating anthropogenic threats to endangered killer whales to inform effective recovery plans.
SCIENTIFIC REPORTS,
7 Author URL.
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Heathcote RJP, Darden SK, Franks DW, Ramnarine IW, Croft DP (2017). Fear of predation drives stable and differentiated social relationships in guppies.
Scientific Reports,
7Abstract:
Fear of predation drives stable and differentiated social relationships in guppies
Social relationships can have important consequences for fitness in animals. Whilst numerous studies have shown that individuals often join larger groups in response to perceived predation risk (i.e. fear of predation), the importance of predation risk in driving the formation and stability of social relationships within groups has been relatively ignored. We experimentally tested how predation threat influenced fine-scale social network structure using Trinidadian guppies (Poecilia reticulata). When perceived predation risk was high, individuals developed stable and more differentiated social ties compared to when perceived risk was low. Intriguingly, social differentiation coincided with shoals being somewhat smaller under high-perceived risk, suggesting a possible conflict between forming stable social relationships and larger social groups. Individuals most at risk of predation (large and bold individuals) showed the most exaggerated responses in several social measures. Taken together, we provide the first experimental evidence that proximate risk of predation can increase the intensity of social relationships and fine-scale social structure in animal populations.
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Ellis S, Franks DW, Nattrass S, Cant MA, Weiss MN, Giles D, Balcomb KC, Croft DP (2017). Mortality risk and social network position in resident killer whales: Sex differences and the importance of resource abundance.
Proceedings of the Royal Society B: Biological Sciences,
284(1865).
Abstract:
Mortality risk and social network position in resident killer whales: Sex differences and the importance of resource abundance
An individual’s ecological environment affects their mortality risk, which in turn has fundamental consequences for life-history evolution. In many species, social relationships are likely to be an important component of an individual’s environment, and therefore their mortality risk. Here, we examine the relationship between social position and mortality risk in resident killer whales (Orcinus orca) using over three decades of social and demographic data. We find that the social position of male, but not female, killer whales in their social unit predicts their mortality risk. More socially integrated males have a significantly lower risk of mortality than socially peripheral males, particularly in years of low prey abundance, suggesting that social position mediates access to resources. Male killer whales are larger and require more resources than females, increasing their vulnerability to starvation in years of low salmon abundance. More socially integrated males are likely to have better access to social information and food-sharing opportunities which may enhance their survival in years of low salmon abundance. Our results show that observable variation in the social environment is linked to variation in mortality risk, and highlight how sex differences in social effects on survival may be linked to sex differences in life-history evolution.
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Bolt SL, Boyland NK, Mlynski DT, James R, Croft DP (2017). Pair housing of dairy calves and age at pairing: Effects on weaning stress, health, production and social networks.
PLoS ONE,
12(1).
Abstract:
Pair housing of dairy calves and age at pairing: Effects on weaning stress, health, production and social networks
The early social environment can influence the health and behaviour of animals, with effects lasting into adulthood. In Europe, around 60% of dairy calves are reared individually during their first eight weeks of life, while others may be housed in pairs or small groups. This study assessed the effects of varying degrees of social contact on weaning stress, health and production during pen rearing, and on the social networks that calves later formed when grouped. Forty female Holstein-Friesian calves were allocated to one of three treatments: individually housed (I, n = 8), pair-housed from day five (P5, n = 8 pairs), and pair-housed from day 28 (P28, n = 8 pairs). From day 48, calves were weaned by gradual reduction of milk over three days, and vocalisations were recorded as a measure of stress for three days before, during and after weaning. Health and production (growth rate and concentrate intakes) were not affected by treatment during the weaning period or over the whole study. Vocalisations were highest post-weaning, and were significantly higher in Icalves than pair-reared calves. Furthermore, P28calves vocalised significantly more than P5calves. The social network of calves was measured for one month after all calves were grouped in a barn, using association data from spatial proximity loggers. We tested for week-week stability, social differentiation and assortment in the calf network. Additionally, we tested for treatment differences in: coefficient of variation (CV) in association strength, percentage of time spent with ex-penmate (P5 and P28 calves only) and weighted degree centrality (the sum of the strength of an individual's associations). The network was relatively stable from weeks one to four and was significantly differentiated, with individuals assorting based on prior familiarity. P5 calves had significantly higher CV in association strength than Icalves in week one (indicating more heterogeneous social associations) but there were no significant treatment differences in week four. The mean percentage of time that individuals spent with their ex-penmate after regrouping decreased from weeks 1-4, though treatment did not affect this. There were also no significant differences in weighted degree centrality between calves in each rearing treatment. These results suggest that early pair-rearing can allow calves the stress buffering benefits of social support (and that this is more effective when calves are paired earlier) without compromising health or production, and sheds light on the early development of social behaviour in cattle.
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Croft DP, Johnstone RA, Ellis S, Nattrass S, Franks DW, Brent LJN, Mazzi S, Balcomb KC, Ford JKB, Cant MA, et al (2017). Reproductive Conflict and the Evolution of Menopause in Killer Whales.
Current Biology,
27(2), 298-304.
Abstract:
Reproductive Conflict and the Evolution of Menopause in Killer Whales
Why females of some species cease ovulation prior to the end of their natural lifespan is a long-standing evolutionary puzzle [1–4]. The fitness benefits of post-reproductive helping could in principle select for menopause [1, 2, 5], but the magnitude of these benefits appears insufficient to explain the timing of menopause [6–8]. Recent theory suggests that the cost of inter-generational reproductive conflict between younger and older females of the same social unit is a critical missing term in classical inclusive fitness calculations (the “reproductive conflict hypothesis” [6, 9]). Using a unique long-term dataset on wild resident killer whales, where females can live decades after their final parturition, we provide the first test of this hypothesis in a non-human animal. First, we confirm previous theoretical predictions that local relatedness increases with female age up to the end of reproduction. Second, we construct a new evolutionary model and show that given these kinship dynamics, selection will favor younger females that invest more in competition, and thus have greater reproductive success, than older females (their mothers) when breeding at the same time. Third, we test this prediction using 43 years of individual-based demographic data in resident killer whales and show that when mothers and daughters co-breed, the mortality hazard of calves from older-generation females is 1.7 times that of calves from younger-generation females. Intergenerational conflict combined with the known benefits conveyed to kin by post-reproductive females can explain why killer whales have evolved the longest post-reproductive lifespan of all non-human animals.
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Silk MJ, Weber N, Steward LC, Delahay RJ, Croft DP, Hodgson DJ, Boots M, McDonald RA (2017). Seasonal variation in daily patterns of social contacts in the European badger meles meles.
Ecology and Evolution,
7(21), 9006-9015.
Abstract:
Seasonal variation in daily patterns of social contacts in the European badger meles meles
Social interactions among hosts influence the persistence and spread of infectious pathogens. Daily and seasonal variation in the frequency and type of social interactions will play an important role in disease epidemiology and, alongside other factors, may have an influence on wider disease dynamics by causing seasonal forcing of infection, especially if the seasonal variation experienced by a population is considerable. We explored temporal variation in within-group contacts in a high-density population of European badgers Meles meles naturally infected with Mycobacterium bovis (the causative agent of bovine tuberculosis). Summer contacts were more likely and of longer duration during the daytime, while the frequency and duration of winter contacts did not differ between day and night. In spring and autumn, within-group contacts peaked at dawn and dusk, corresponding with when they were of shortest duration with reduced potential for aerosol transmission of pathogens. Summer and winter could be critical for transmission of M. bovis in badgers, due to the high frequency and duration of contacts during resting periods, and we discuss the links between this result and empirical disease data. This study reveals clear seasonality in daily patterns of contact frequency and duration in species living in stable social groups, suggesting that changes in social contacts could drive seasonal forcing of infection in wildlife populations even when the number of individuals interacting remains similar.
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Rose PE, Croft DP (2017). Social bonds in a flock bird: Species differences and seasonality in social structure in captive flamingo flocks over a 12-month period.
Applied Animal Behaviour Science,
193, 87-97.
Abstract:
Social bonds in a flock bird: Species differences and seasonality in social structure in captive flamingo flocks over a 12-month period
Social network analysis (SNA) is a popular tool for investigating key components of sociality in free-living populations, and is growing in its application to captive animal systems. For social species held in captivity, welfare may be improved if protocols for care take key aspects of sociality into account. Individuals may benefit from investment in social affiliations and these relationships may exist over many years. Here we examine patterns of association that exist within captive flamingo (Phoenicopteridae) flocks across a 12-month period. We test the hypotheses that birds will show stable bonds with specific individuals within a flock, and that these bonds will be stable over time. Flamingos are well known for being highly-gregarious birds yet the importance of specific relationships between birds in a flock is still poorly defined. Four flocks of captive flamingos, of five species were included in the study at WWT Slimbridge Wetland Centre to assess the strength and consistency of bonds between individuals. Social associations were scored for all flocks from March 2012 to March 2013, with an average of 98 days/sample time/flock. Each flock showed evidence of specific preferential associations between birds, which, in some cases, remained constant over the period of observations. Networks highlight the existence of inter- and intrasexual bonds present in all flamingo flocks. Mantel tests determine that strong dyadic bonds are maintained in (spring/summer) and out (autumn/winter) of the breeding season. Measuring social behaviour may provide an insight into flamingo welfare as changes in the number of associates and mean time spent associating appears to be impacted upon by environmental variables, such as enclosure type. As consistent partnerships are maintained between birds (of all flocks of all species) across season, there are potential implications for breeding and mate selection if new partnerships are not being formed at breeding times.
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Stevens CH, Croft DP, Paull GC, Tyler CR (2017). Stress and welfare in ornamental fishes: what can be learned from aquaculture?.
Journal of Fish Biology,
91(2), 409-428.
Abstract:
Stress and welfare in ornamental fishes: what can be learned from aquaculture?
The ornamental fish trade is estimated to handle up to 1·5 billion fishes. Transportation and handling of fishes imposes a range of stressors that can result in mortality at rates of up to 73%. These rates vary hugely, however, and can be as low as 2%, because they are generally estimated rather than based on experimental work. Given the numbers of ornamental fishes traded, any of the estimated mortality rates potentially incur significant financial losses and serious welfare issues. Industry bodies, such as the Ornamental Aquatic Trade Association (OATA), have established standards and codes of best practice for handling fishes, but little scientific research has been conducted to understand the links between stress, health and welfare in ornamental species. In aquaculture, many of the same stressors occur as those in the ornamental trade, including poor water quality, handling, transportation, confinement, poor social and physical environment and disease and in this sector directed research and some resulting interventions have resulted in improved welfare standards. This review considers the concept of welfare in fishes and evaluates reported rates of mortality in the ornamental trade. It assesses how the stress response can be quantified and used as a welfare indicator in fishes. It then analyses whether lessons from aquaculture can be usefully applied to the ornamental fish industry to improve welfare. Finally, this analysis is used to suggest how future research might be directed to help improve welfare in the ornamental trade.
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Silk MJ, Croft DP, Delahay RJ, Hodgson DJ, Weber N, Boots M, McDonald RA (2017). The application of statistical network models in disease research.
Methods in Ecology and Evolution,
8(9), 1026-1041.
Abstract:
The application of statistical network models in disease research
Host social structure is fundamental to how infections spread and persist, and so the statistical modelling of static and dynamic social networks provides an invaluable tool to parameterise realistic epidemiological models. We present a practical guide to the application of network modelling frameworks for hypothesis testing related to social interactions and epidemiology, illustrating some approaches with worked examples using data from a population of wild European badgers Meles meles naturally infected with bovine tuberculosis. Different empirical network datasets generate particular statistical issues related to non-independence and sampling constraints. We therefore discuss the strengths and weaknesses of modelling approaches for different types of network data and for answering different questions relating to disease transmission. We argue that statistical modelling frameworks designed specifically for network analysis offer great potential in directly relating network structure to infection. They have the potential to be powerful tools in analysing empirical contact data used in epidemiological studies, but remain untested for use in networks of spatio-temporal associations. As a result, we argue that developments in the statistical analysis of empirical contact data are critical given the ready availability of dynamic network data from bio-logging studies. Furthermore, we encourage improved integration of statistical network approaches into epidemiological research to facilitate the generation of novel modelling frameworks and help extend our understanding of disease transmission in natural populations.
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Edenbrow M, Bleakley BH, Darden SK, Tyler CR, Ramnarine IW, Croft DP (2017). The evolution of cooperation: Interacting phenotypes among social partners.
American Naturalist,
189(6), 630-643.
Abstract:
The evolution of cooperation: Interacting phenotypes among social partners
Models of cooperation among nonkin suggest that social assortment is important for the evolution of cooperation. Theory predicts that interacting phenotypes, whereby an individual’s behavior depends on the behavior of its social partners, can drive such social assortment. We measured repeated indirect genetic effects (IGEs) during cooperative predator inspection in eight populations of Trinidadian guppies (Poecilia reticulata) that vary in their evolutionary history of predation. Four broad patterns emerged that were dependent on river, predation history, and sex: (i) current partner behavior had the largest effect on focal behavior, with fish from low-predation habitats responding more to their social partners than fish from high-predation habitats; (ii) different focal/partner behavior combinations can generate cooperation; (iii) some high-predation fish exhibited carryover effects across social partners; and (iv) high-predation fish were more risk averse. These results provide the first large-scale comparison of interacting phenotypes during cooperation across wild animal populations, highlighting the potential importance of IGEs in maintaining cooperation. Intriguingly, while focal fish responded strongly to current social partners, carryover effects between social partners suggest generalized reciprocity (in which one helps anyone if helped by someone) may contribute to the evolution of cooperation in some, but not all, populations of guppies.
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Silk MJ, Croft DP, Delahay RJ, Hodgson DJ, Boots M, Weber N, McDONALD RA (2017). Using social network measures in wildlife disease ecology, epidemiology, and management.
BioScience,
67(3), 245-257.
Abstract:
Using social network measures in wildlife disease ecology, epidemiology, and management
Contact networks, behavioral interactions, and shared use of space can all have important implications for the spread of disease in animals. Social networks enable the quantification of complex patterns of interactions; therefore, network analysis is becoming increasingly widespread in the study of infectious disease in animals, including wildlife. We present an introductory guide to using social-network-Analytical approaches in wildlife disease ecology, epidemiology, and management. We focus on providing detailed practical guidance for the use of basic descriptive network measures by suggesting the research questions to which each technique is best suited and detailing the software available for each. We also discuss how using network approaches can be used beyond the study of social contacts and across a range of spatial and temporal scales. Finally, we integrate these approaches to examine how network analysis can be used to inform the implementation and monitoring of effective disease management strategies.
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Firth JA, Voelkl B, Crates RA, Aplin LM, Biro D, Croft DP, Sheldon BC (2017). Wild birds respond to flockmate loss by increasing their social network associations to others.
Proceedings of the Royal Society B: Biological Sciences,
284(1854).
Abstract:
Wild birds respond to flockmate loss by increasing their social network associations to others
Understanding the consequences of losing individuals from wild populations is a current and pressing issue, yet how such loss influences the social behaviour of the remaining animals is largely unexplored. Through combining the automated tracking of winter flocks of over 500 wild great tits (Parus major) with removal experiments, we assessed how individuals’ social network positions responded to the loss of their social associates. We found that the extent of flockmate loss that individuals experienced correlated positively with subsequent increases in the number of their social associations, the average strength of their bonds and their overall connectedness within the social network (defined as summed edge weights). Increased social connectivity was not driven by general disturbance or changes in foraging behaviour, but by modifications to fine-scale social network connections in response to losing their associates. Therefore, the reduction in social connectedness expected by individual loss may be mitigated by increases in social associations between remaining individuals. Given that these findings demonstrate rapid adjustment of social network associations in response to the loss of previous social ties, future research should examine the generality of the compensatory adjustment of social relations in ways that maintain the structure of social organization.
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2016
Croft DP, Darden SK, Wey TW (2016). Current directions in animal social networks.
Current Opinion in Behavioral Sciences,
12, 52-58.
Abstract:
Current directions in animal social networks
A social network approach provides a framework to study the link between individual behaviour and population-level patterns and processes. Studies have demonstrated how animal social network structure can be influenced by factors ranging from characteristics of the environment to characteristics of the individual, such as developmental experience and personality. At the level of the individual, the patterning of social connections can be an important determinant of fitness, predicting both survival and reproductive success. At the population level, network structure can influence the patterning of ecological and evolutionary processes, such as frequency-dependant selection and disease and information transmission.
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Killen SS, Croft DP, Salin K, Darden SK (2016). Male sexually coercive behaviour drives increased swimming efficiency in female guppies.
Functional Ecology,
30(4), 576-583.
Abstract:
Male sexually coercive behaviour drives increased swimming efficiency in female guppies
Sexual coercion of females by males is widespread across sexually reproducing species. It stems from a conflict of interest over reproduction and exerts selective pressure on both sexes. For females, there is often a significant energetic cost of exposure to male sexually coercive behaviours. Our understanding of the efficiency of female resistance to male sexually coercive behaviour is key to understanding how sexual conflict contributes to population level dynamics and ultimately to the evolution of sexually antagonistic traits. Overlooked within this context are plastic physiological responses of traits within the lifetime of females that could moderate the energetic cost imposed by coercive males. Here, we examined whether conflict over the frequency and timing of mating between male and female guppies Poecilia reticulata can induce changes in swimming performance and aerobic capacity in females as they work to escape harassment by males. Females exposed to higher levels of harassment over a 5-month period used less oxygen to swim at a given speed, but displayed no difference in resting metabolic rate, maximal metabolic rate, maximal sustained swimming speed or aerobic scope compared to females receiving lower levels of harassment. The observed increase in swimming efficiency is at least partially related to differences in swimming mechanics, likely brought on by a training effect of increased activity, as highly harassed females spent less time performing pectoral fin-assisted swimming. Sexual conflict results in sexually antagonistic traits that impose a variety of costs, but our results show that females can reduce costs through phenotypic plasticity. It is also possible that phenotypic plasticity in swimming physiology or mechanics in response to sexual coercion can potentially give females more control over matings and affect which male traits are under selection.
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Franks DW, Nattrass S, Brent LJN, Whitehead H, Foote AD, Mazzi S, Ford JKB, Balcomb KC, Cant MA, Croft DP, et al (2016). The significance of postreproductive lifespans in killer whales: a comment on Robeck et al.
Journal of Mammalogy,
97(3), 906-909.
Abstract:
The significance of postreproductive lifespans in killer whales: a comment on Robeck et al.
Robeck et al. (2015) claim that reproductive and actuarial senescence is common in mammalian species and therefore not an unexpected finding in killer whales. However, in most mammals, reproductive and somatic senescence are aligned, and reproduction gradually declines with age. In contrast, there is a substantial evidence that reproductive senescence is unusually accelerated relative to somatic senescence in resident killer whales, resulting in a prolonged postreproductive lifespan. We demonstrate that a postreproductive lifespan is a key component of resident killer whale life history, and is robust to reasonable error in age estimates.
Abstract.
Boyland NK, Mlynski DT, James R, Brent LJN, Croft DP (2016). The social network structure of a dynamic group of dairy cows: from individual to group level patterns.
Applied Animal Behaviour Science,
174, 1-10.
Abstract:
The social network structure of a dynamic group of dairy cows: from individual to group level patterns
Social relationships have been shown to significantly impact individual and group success in wild animal populations, but are largely ignored in farm animal management. There are substantial gaps in our knowledge of how farm animals respond to their social environment, which varies greatly between farms but is commonly unstable due to regrouping. Fundamental to addressing these gaps is an understanding of the social network structure resulting from the patterning of relationships between individuals in a group. Here, we investigated the social structure of a group of 110 lactating dairy cows during four one-month periods. Spatial proximity loggers collected data on associations between cows, allowing us to construct social networks. First we demonstrate that proximity loggers can be used to measure relationships between cows; proximity data was significantly positively correlated to affiliative interactions but had no relationship with agonistic interactions. We measured group-level patterns by testing for community structure, centralisation and repeatability of network structure over time. We explored individual-level patterns by measuring social differentiation (heterogeneity of social associations) and assortment of cows in the network by lactation number, breed, gregariousness and milk production. There was no evidence that cows were subdivided into social communities; individuals belonged to a single cluster and networks showed significant centralisation. Repeatability of the social network was low, which may have consequences for animal welfare. Individuals formed differentiated social relationships and there was evidence of positive assortment by traits; cows associated more with conspecifics of similar lactation number in all study periods. There was also positive assortment by breed, gregariousness and milk production in some study periods. There is growing interest in the farming industry in the impact of social factors on production and welfare; this study takes an important step towards understanding social dynamics.
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2015
Vázquez Diosdado JA, Barker ZE, Hodges HR, Amory JR, Croft DP, Bell NJ, Codling EA (2015). Classification of behaviour in housed dairy cows using an accelerometer-based activity monitoring system.
Animal Biotelemetry,
3(1).
Abstract:
Classification of behaviour in housed dairy cows using an accelerometer-based activity monitoring system
Background: Advances in bio-telemetry technology have made it possible to automatically monitor and classify behavioural activities in many animals, including domesticated species such as dairy cows. Automated behavioural classification has the potential to improve health and welfare monitoring processes as part of a Precision Livestock Farming approach. Recent studies have used accelerometers and pedometers to classify behavioural activities in dairy cows, but such approaches often cannot discriminate accurately between biologically important behaviours such as feeding, lying and standing or transition events between lying and standing. In this study we develop a decision-tree algorithm that uses tri-axial accelerometer data from a neck-mounted sensor to both classify biologically important behaviour in dairy cows and to detect transition events between lying and standing. Results: Data were collected from six dairy cows that were monitored continuously for 36 h. Direct visual observations of each cow were used to validate the algorithm. Results show that the decision-tree algorithm is able to accurately classify three types of biologically relevant behaviours: lying (77.42 % sensitivity, 98.63 % precision), standing (88.00 % sensitivity, 55.00 % precision), and feeding (98.78 % sensitivity, 93.10 % precision). Transitions between standing and lying were also detected accurately with an average sensitivity of 96.45 % and an average precision of 87.50 %. The sensitivity and precision of the decision-tree algorithm matches the performance of more computationally intensive algorithms such as hidden Markov models and support vector machines. Conclusions: Biologically important behavioural activities in housed dairy cows can be classified accurately using a simple decision-tree algorithm applied to data collected from a neck-mounted tri-axial accelerometer. The algorithm could form part of a real-time behavioural monitoring system in order to automatically detect dairy cow health and welfare status.
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Brent LJN, Franks DW, Foster EA, Balcomb KC, Cant MA, Croft DP (2015). Ecological knowledge, leadership, and the evolution of menopause in killer whales.
Current Biology,
25(6), 746-750.
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Rose PE, Croft DP (2015). Evidence of directed interactions between individuals in captive flamingo flocks.
Wildfowl,
65, 121-132.
Abstract:
Evidence of directed interactions between individuals in captive flamingo flocks
Information on social behaviour traits can be inferred from observed associations or measured as the frequency of direct interactions between individuals. For some species, information on interactions between individuals, and the form that these interactions take, is limited. This paper describes three social interactions (affiliative, mate-guarding and directed aggression) seen in captive flamingos (Phoenicoparrus sp. and Phoenicopterus sp.) that could be of help to those studying flamingo social behaviour, by adding explanation of direct interactions to the overall flamingo ethogram. Information on how flamingos organise their social structure appears infrequently in the literature, and what (if any) specific social interactions are performed from one bird to another can be lacking in description and definition. The behaviours explained in this paper provide an insight into the social lives of flamingos that can give support to further, deeper, studies into social hierarchy and social affiliation.
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Silk MJ, Jackson AL, Croft DP, Colhoun K, Bearhop S (2015). The consequences of unidentifiable individuals for the analysis of an animal social network.
Animal Behaviour,
104, 1-11.
Abstract:
The consequences of unidentifiable individuals for the analysis of an animal social network
Social network analysis is pervasive in understanding animal social systems, and provides information about how individuals vary in their social strategies. Many long-term studies comprising uniquely marked individuals use social network analysis as an analytical tool. However, the assumption that it is possible to make inferences using network metrics calculated using a subset of the population has yet to be investigated in an animal social network. We use a simulation study of networks derived from social interactions in a typical fluid fission-fusion social system to determine the precision and accuracy of measures of individual social position based on incomplete knowledge. We show that individual social positions measured in partial social networks correlate strongly with positions in the full social network. This correlation typically becomes stronger as the size of the simulated population is increased and is largely not affected by network density. The choice of network metric has an important effect on the precision of partial networks only when they include a small subset of the population and therefore caution is advised using some of these measures in small partial networks. This work demonstrates that valid inferences about individual social position and strategy can be made using partial networks in a wide range of animal social networks, highlighting the value of applying these methods in large long-term study populations.
Abstract.
Croft DP, Brent LJN, Franks DW, Cant MA (2015). The evolution of prolonged life after reproduction.
TRENDS IN ECOLOGY & EVOLUTION,
30(7), 407-416.
Author URL.
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Rose PE, Croft DP (2015). The potential of Social Network Analysis as a tool for the management of zoo animals.
ANIMAL WELFARE,
24(2), 123-138.
Author URL.
Tranmer M, Marcum CS, Morton FB, Croft DP, de Kort SR (2015). Using the relational event model (REM) to investigate the temporal dynamics of animal social networks.
Animal Behaviour,
101, 99-105.
Abstract:
Using the relational event model (REM) to investigate the temporal dynamics of animal social networks
Social dynamics are of fundamental importance in animal societies. Studies on nonhuman animal social systems often aggregate social interaction event data into a single network within a particular time frame. Analysis of the resulting network can provide a useful insight into the overall extent of interaction. However, through aggregation, information is lost about the order in which interactions occurred, and hence the sequences of actions over time. Many research hypotheses relate directly to the sequence of actions, such as the recency or rate of action, rather than to their overall volume or presence. Here, we demonstrate how the temporal structure of social interaction sequences can be quantified from disaggregated event data using the relational event model (REM). We first outline the REM, explaining why it is different from other models for longitudinal data, and how it can be used to model sequences of events unfolding in a network. We then discuss a case study on the European jackdaw, Corvus monedula, in which temporal patterns of persistence and reciprocity of action are of interest, and present and discuss the results of a REM analysis of these data. One of the strengths of a REM analysis is its ability to take into account different ways in which data are collected. Having explained how to take into account the way in which the data were collected for the jackdaw study, we briefly discuss the application of the model to other studies. We provide details of how the models may be fitted in the R statistical software environment and outline some recent extensions to the REM framework.
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2014
Rose PE, Croft DP, Lee R (2014). A review of captive flamingo (Phoenicopteridae) welfare: a synthesis of current knowledge and future directions.
International Zoo Yearbook,
48(1), 139-155.
Abstract:
A review of captive flamingo (Phoenicopteridae) welfare: a synthesis of current knowledge and future directions
Flamingos are ubiquitous captive species (potentially the world's most commonly kept zoo bird) that have long lifespans and unique breeding cycles. In-depth research into the links between provision (enclosure, husbandry), behavioural performance (reflecting internal motivation) and perceived welfare state (from behavioural cues) can inform management for good welfare over the many decades of a bird's life, and benefit reproductive output. Here, the published literature on flamingo husbandry is reviewed, with reference to our current understanding of flamingo behaviour in the wild. Evaluation of whole-flock time budgets and assessment of behavioural diversity can highlight any deviation from a norm. Several published works suggest ways of improving breeding success in captive flamingos by re-evaluating husbandry routines as well as highlighting minimum numbers of birds per flock for 'good welfare'. Research has shown that some aspects of zoo-flamingo activity can match that of wild birds. Further examination of specific behaviour patterns, as well as the motivations for these, would allow for evidence-based enclosure design and provision of species-specific behavioural husbandry. Future research topics covering social support, foraging activity and developing a definition of 'positive welfare activity' would further enhance zoo management practices for these birds. © 2014 the Zoological Society of London.
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Krause J, James R, Franks D, Croft D (2014).
Animal Social Networks., Oxford University Press.
Abstract:
Animal Social Networks
Abstract.
Croft DP, Edenbrow M, Darden SK (2014). Assortment in social networks and the evolution of cooperation. In Krause J, James R, Franks D, Croft DP (Eds.) Animal Social Networks, Oxford University Press.
Wilson ADM, Krause S, James R, Croft DP, Ramnarine IW, Borner KK, Clement RJG, Krause J (2014). Dynamic social networks in guppies (Poecilia reticulata).
BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY,
68(6), 915-925.
Author URL.
Jacoby DMP, Fear LN, Sims DW, Croft DP (2014). Shark personalities? Repeatability of social network traits in a widely distributed predatory fish.
BEHAVIORAL ECOLOGY AND SOCIOBIOLOGY,
68(12), 1995-2003.
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Kurvers RHJM, Krause J, Croft DP, Wilson ADM, Wolf M (2014). The evolutionary and ecological consequences of animal social networks: emerging issues.
Trends Ecol Evol,
29(6), 326-335.
Abstract:
The evolutionary and ecological consequences of animal social networks: emerging issues.
The first generation of research on animal social networks was primarily aimed at introducing the concept of social networks to the fields of animal behaviour and behavioural ecology. More recently, a diverse body of evidence has shown that social fine structure matters on a broader scale than initially expected, affecting many key ecological and evolutionary processes. Here, we review this development. We discuss the effects of social network structure on evolutionary dynamics (genetic drift, fixation probabilities, and frequency-dependent selection) and social evolution (cooperation and between-individual behavioural differences). We discuss how social network structure can affect important coevolutionary processes (host-pathogen interactions and mutualisms) and population stability. We also discuss the potentially important, but poorly studied, role of social network structure on dispersal and invasion. Throughout, we highlight important areas for future research.
Abstract.
Author URL.
Silk MJ, Croft DP, Tregenza T, Bearhop S (2014). The importance of fission-fusion social group dynamics in birds.
IBIS,
156(4), 701-715.
Author URL.
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2013
Wilson ADM, Croft DP, Krause J (2013). Social networks in elasmobranchs and teleost fishes. Fish and Fisheries
Boyland NK, James R, Mlynski DT, Madden JR, Croft DP (2013). Spatial proximity loggers for recording animal social networks: Consequences of inter-logger variation in performance.
Behavioral Ecology and Sociobiology,
67(11), 1877-1890.
Abstract:
Spatial proximity loggers for recording animal social networks: Consequences of inter-logger variation in performance
Social network analysis has become an increasingly popular method to link individual behaviour to population level patterns (and vice versa). Technological advances of recent years, such as the development of spatial proximity loggers, have enhanced our abilities to record contact patterns between animals. However, loggers are often deployed without calibration which may lead to sampling biases and spurious results. In particular, loggers may differ in their performance (i.e. some loggers may over-sample and other loggers may under-sample social associations). However, the consequences of inter-logger variation in logging performance has not been thoroughly considered or quantified. In this study, proximity loggers made by Sirtrack Ltd. were fitted to 20 dairy cows over a 3-week period. Contact records resulting from field deployment demonstrated variability in logger performance when recording contact duration, which was highly consistent for each logger over time. Testing loggers under standardised conditions suggested that inter-logger variation observed in the field was due to a combination of intrinsic variation in devices, and environmental/behavioural effects. We demonstrate the potential consequences that inter-logger variation in logging performance can have for social network analysis; particularly how measures of connectivity can be biased by logging performance. Finally, we suggest some approaches to correct data generated by proximity loggers with imperfect performance, that should be used to improve the robustness of future analyses. © 2013 Springer-Verlag Berlin Heidelberg.
Abstract.
2012
Foster EA, Franks DW, Mazzi S, Darden SK, Balcomb KC, Ford JKB, Croft DP (2012). Adaptive prolonged postreproductive life span in killer whales.
Science,
337(6100).
Abstract:
Adaptive prolonged postreproductive life span in killer whales.
Prolonged life after reproduction is difficult to explain evolutionarily unless it arises as a physiological side effect of increased longevity or it benefits related individuals (i.e. increases inclusive fitness). There is little evidence that postreproductive life spans are adaptive in nonhuman animals. By using multigenerational records for two killer whale (Orcinus orca) populations in which females can live for decades after their final parturition, we show that postreproductive mothers increase the survival of offspring, particularly their older male offspring. This finding may explain why female killer whales have evolved the longest postreproductive life span of all nonhuman animals.
Abstract.
Author URL.
Keedwell E, Morley M, Croft D (2012). Continuous Trait-Based Particle Swarm Optimisation (CTB-PSO).
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics),
7461 LNCS, 342-343.
Abstract:
Continuous Trait-Based Particle Swarm Optimisation (CTB-PSO)
In natural flocks, individuals are often of the same species, but there exists considerable variation in the traits possessed by each individual. In much the same way as humans display varied levels of aggression, gregariousness and inquisitiveness, so do the animals on which PSO is based [1]. Recent research has shown that this disparity of behaviour is very important in the ability of the flock to solve problems effectively, which might have profound implications for PSO. One of the key aspects is that although certain behaviour types (e.g. more adventurous individuals) might individually be better at problem solving; selecting for a group that all have adventurous traits has been shown to reduce the performance of the flock as a whole [1]. Therefore a flock that has a variety of behaviours leads to better performance in natural systems and it is this that motivates the work here. This paper explores a variant of PSO known as Continuous Trait-Based PSO (CTB-PSO) where individuals within a swarm have traits based on a continuous scale as opposed to discrete behaviour groupings. © 2012 Springer-Verlag.
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Jacoby DMP, Brooks EJ, Croft DP, Sims DW (2012). Developing a deeper understanding of animal movements and spatial dynamics through novel application of network analyses.
METHODS IN ECOLOGY AND EVOLUTION,
3(3), 574-583.
Author URL.
Bode NWF, Franks DW, Jamie Wood A, Piercy JJB, Croft DP, Codling EA (2012). Distinguishing social from nonsocial navigation in moving animal groups.
American Naturalist,
179(5), 621-632.
Abstract:
Distinguishing social from nonsocial navigation in moving animal groups
Many animals, such as migrating shoals of fish, navigate in groups. Knowing the mechanisms involved in animal navigation is important when it comes to explaining navigation accuracy, dispersal patterns, population and evolutionary dynamics, and consequently, the design of conservation strategies. When navigating toward a common target, animals could interact socially by sharing available information directly or indirectly, or each individual could navigate by itself and aggregations may not disperse because all animals are moving toward the same target. Here we present an analysis technique that uses individual movement trajectories to determine the extent to which individuals in navigating groups interact socially, given knowledge of their target. The basic idea of our approach is that the movement directions of individuals arise from a combination of responses to the environment and to other individuals. We estimate the relative importance of these responses, distinguishing between social and nonsocial interactions. We develop and test our method, using simulated groups, and we demonstrate its applicability to empirical data in a case study on groups of guppies moving toward shelter in a tank. Our approach is generic and can be extended to different scenarios of animal group movement. © 2012 by the University of Chicago.
Abstract.
Edenbrow M, Croft DP (2012). Environmental and genetic effects shape the development of personality traits in the mangrove killifish Kryptolebias marmoratus. Oikos
Edenbrow M, Croft DP (2012). Kin and familiarity influence association preferences and aggression in the mangrove killifish Kryptolebias marmoratus.
J Fish Biol,
80(3), 503-518.
Abstract:
Kin and familiarity influence association preferences and aggression in the mangrove killifish Kryptolebias marmoratus.
Association preferences and aggression intensity were investigated in relation to kin and familiarity in the self-fertilizing, clonal vertebrate, the mangrove killifish Kryptolebias marmoratus. Results indicated that fish preferentially associated with and exhibited less intense aggression towards members of their own genotype (kin), compared to members of a different genotype (non-kin). Furthermore, when fish were presented with stimulus groups of the same genotype that were familiar or unfamiliar, fish preferentially associated with and exhibited lower aggression intensity directed towards familiar groups. These results indicate that this species prefer to associate with both kin and familiar individuals and modulate aggression accordingly. These results are discussed with reference to the adaptive benefits of kin recognition and preferences for familiars, and place results within the context of current knowledge of the ecology of K. marmoratus.
Abstract.
Author URL.
Edenbrow M, Croft DP (2012). Sequential hermaphroditism and personality in a clonal vertebrate: the mangrove killifish.
Behav Processes,
90(2), 229-237.
Abstract:
Sequential hermaphroditism and personality in a clonal vertebrate: the mangrove killifish.
Individuals are regularly documented to consistently differ in their behavioural types (BTs). For example, some individuals are bold whereas others are shy. Within the human personality literature, the big five personality dimensions are commonly documented to be sex-specific with testosterone suggested to underpin traits such as aggressiveness. In non-human animals recent research suggests sex-specific BT expression may be influenced by ecology, mating system and sexual selection. While most research on sex-specific personality has focused on dioecious species, we explore sex differences in BT expression in a sequential hermaphrodite the mangrove killifish. We replicate within 7 isogenic genotypes and investigate sex differences (hermaphrodite and secondary male) in three BTs (exploration, boldness and aggression). This approach allows us to investigate sex differences in BT expression whilst controlling for genetic variation. In this study we find that both secondary males and hermaphrodites are repeatable at the individual level yet there was no difference between the sexes in average BT scores. Furthermore, aggression scores differed between genotypes, and were repeatable at the genotype level, suggesting strong genetic control. Finally, male boldness was significantly more repeatable than hermaphrodites potentially supporting recent proposals relating to sexual selection. We document a behavioural syndrome in male fish with bolder individuals being more aggressive, this behavioural syndrome was not observed however in hermaphrodites. In contrast to a previous developmental study in this species exploration did not correlate with either aggression or boldness in either males or hermaphrodites.
Abstract.
Author URL.
Jacoby DMP, Croft DP, Sims DW (2012). Social behaviour in sharks and rays: Analysis, patterns and implications for conservation. Fish and Fisheries, 13(4), 399-417.
Foster EA, Franks DW, Morrell LJ, Balcomb KC, Parsons KM, van Ginneken A, Croft DP (2012). Social network correlates of food availability in an endangered population of killer whales, Orcinus orca.
ANIMAL BEHAVIOUR,
83(3), 731-736.
Author URL.
Jacoby DMP, Sims DW, Croft DP (2012). The effect of familiarity on aggregation and social behaviour in juvenile small spotted catsharks Scyliorhinus canicula.
J Fish Biol,
81(5), 1596-1610.
Abstract:
The effect of familiarity on aggregation and social behaviour in juvenile small spotted catsharks Scyliorhinus canicula.
This study was designed to address whether juvenile small spotted catsharks Scyliorhinus canicula aggregate and to determine whether potential aggregation is underpinned by social preferences for conspecifics. Using controlled and replicated experiments, the role of familiarity as a potential mechanism driving aggregation and social behaviour in this species was considered. Observed S. canicula association data compared to null model simulations of random distributions revealed differences in aggregation under different social contexts. Only familiar juvenile S. canicula aggregated more than would be expected from random distribution across their habitat. Familiarity increased the mean number of groups but did not significantly affect mean group size. Significant preference and avoidance behaviour across all groups were also observed. Furthermore, the strength of social attraction, quantified by the mean association index, was significantly higher in groups containing familiar individuals. Mixed familiar and unfamiliar treatments were also conducted to test for within- and between-group effects, finding high variation across replicates with some groups assorting by familiarity and others not. It is believed that this study is the first to examine experimentally the influence of conspecific familiarity on aggregation behaviour in sharks. These results not only imply a functional benefit to aggregation, but also suggest that persistent social affiliation is likely to influence dispersal following hatching in this small benthic elasmobranch.
Abstract.
Author URL.
Griffiths AM, Jacoby DMP, Casane D, McHugh M, Croft DP, Genner MJ, Sims DW (2012). The first analysis of multiple paternity in an oviparous shark species, the small-spotted catshark (Scyliorhinus canicula L.). Journal of Heredity, 2(103), 166-73.
Croft DP, Hamilton PB, Darden SK, Jacoby DMP, James R, Bettaney EM, Tyler CR (2012). The role of relatedness in structuring the social network of a wild guppy population. Oecologia, 1-9.
2011
Guttridge TL, Gruber SH, DiBattista JD, Feldheim KA, Krause S, Croft DP, Krause J (2011). Assortative interactions and leadership in free-ranging population of juvenile lemon sharks, Negaprion brevirostris. Marine Ecology Progress Series, 423, 235-245.
Edenbrow M, Croft DP (2011). Behavioural types and life history strategies during ontogeny in the mangrove killifish, Kryptolebias marmoratus.
Animal Behaviour,
82, 731-741.
Abstract:
Behavioural types and life history strategies during ontogeny in the mangrove killifish, Kryptolebias marmoratus
Consistent differences in behaviour, termed behavioural types (BTs) are well documented in the animal kingdom. Relatively little is known, however, about how and why consistency is maintained within populations. In recent years, theoretical work suggests that life history trade-offs may be an important mechanism driving the maintenance of interindividual variation in BTs. We used a laboratory population of a clonal vertebrate, the mangrove killifish, as a model organism. This fish is an internally self-fertilizing simultaneous hermaphrodite that exhibits within-genotype homozygosity. We utilized 20 genotypes to examine BT plasticity (boldness and exploration), the development of behavioural correlations, and relationships between life history strategy and BTs at five age points during ontogeny. We found that BT scores increased during early ontogeny and reached an asymptote near sexual maturity. We also found considerable variation in BT developmental plasticity at the genotype level. Moreover, although genotypes exhibited high levels of plasticity in BTs, strong, significant positive correlations between exploration and boldness emerged from day 61 onwards. Furthermore, we observed no difference between genotypes in growth rate and growth was unrelated to BTs. Contrary to our predictions, we found that while genotypes differed in their age at first reproduction and reproductive output, these differences were unrelated to BT expression prior to and following sexual maturity. We discuss these results in relation to mechanisms proposed to drive interindividual variation in BTs and we highlight the potential of the mangrove killifish as a model organism for animal personality studies
Abstract.
Croft DP, Edenbrow M, Darden SK, Ramnarine I, van Oosterhout C, Cable J (2011). Effect of gyrodactylid ectoparasites on host behaviour and social network structure in guppies Poecilia reticulata.
Behavioral Ecology and Sociobiology,
65, 2219-2227.
Abstract:
Effect of gyrodactylid ectoparasites on host behaviour and social network structure in guppies Poecilia reticulata
Understanding how individuals modify their social interactions in response to infectious disease is of central importance for our comprehension of how disease dynamics operate in real-world populations. Whilst a significant amount of theoretical work has modelled disease transmission using network models, we have comparatively little understanding of how infectious disease impacts on the social behaviour of individuals and how these effects scale up to the level of the population. We experimentally manipulated the parasite load of female guppies (Poecilia reticulata) and introduced fish either infected with the ectoparasites Gyrodactylus spp. (experimental) or uninfected (control) into replicated semi-natural populations of eight size-matched female guppies. We quantified the behaviour and social associations of both the introduced fish and the population fish. We found that infected experimental fish spent less time associating with the population fish than the uninfected control fish. Using information on which fish initiated shoal fission (splitting) events, our results demonstrate that the population fish actively avoided infected experimental fish. We also found that the presence of an infected individual resulted in a continued decline in social network clustering up to at least 24 h after the introduction of the infected fish, whereas in the control treatment, the clustering coefficient showed an increase at this time point. These results demonstrate that the presence of a disease has implications for both the social associations of infected individuals and for the social network structure of the population, which we predict will have consequences for infectious disease transmission.
Abstract.
Mourabit S, Edenbrow M, Croft DP, Kudoh1 T (2011). Embryonic Development of the Self-fertilizing Mangrove Killifish Kryptolebias marmoratus. Developmental Dynamics(240), 1694-1704.
Edenbrow M, Darden SK, Ramnarine IW, Evans JP, James R, Croft DP (2011). Environmental effects on social interaction networks and male reproductive behaviour in guppies, Poecilia reticulata.
Animal Behaviour,
81(3), 551-558.
Abstract:
Environmental effects on social interaction networks and male reproductive behaviour in guppies, Poecilia reticulata
In social species, the structure and patterning of social interactions have implications for the opportunities for sexual interactions. We used social network analysis to explore the effect of habitat structural complexity on the social and sexual behaviour of male Trinidadian guppies. We used replicated seminatural pools in which we quantified male social network structure and reproductive behaviour under simple and complex habitats. In addition, we compared two populations of guppies that differed in their evolutionary history of predation (one high, one low). The level of habitat complexity did not significantly affect social network structure. However, social networks differed significantly between populations, which we suggest is due to differences in predator experience. Males from the high-predation population had greater overall social network differentiation and fewer male-male associations than their low-risk counterparts. Contrary to our prediction that males would associate more frequently with relatively large (more fecund) females, we observed a negative correlation between female size and the strength of male-female associations. We also found no effect of population or habitat complexity on either harassment or sexual network structures. There was, however, a significant interaction between habitat structure and population on the expression of reproductive strategies, with high-predation males expressing fewer sigmoid displays in the complex habitat and the opposite trend in low-predation males. We suggest this pattern is driven by population differences in male-male competition. We discuss our results in the context of the evolution of social structure and male reproductive strategies. © 2010 the Association for the Study of Animal Behaviour.
Abstract.
Croft DP, Madden J, Franks D, James R (2011). Hypothesis testing in animal social networks. Trends in Ecology and Evolution, 26, 502-507.
Krause J, Wilson AMD, Croft DP (2011). New technology facilitates the study of social networks. Trends in Ecology and Evolution, 26, 5-6.
Krause J, James R, Croft DP (2011). Personality in the context of social networks.
Philosophical Transactions of the Royal Society B: Biological Sciences, 4099-4106.
Abstract:
Personality in the context of social networks
There is great interest in environmental effects on the development and evolution of animal personality traits. An important component of an individual's environment is its social environment. However, few studies look beyond dyadic relationships and try to place the personality of individuals in the context of a social network. Social network analysis provides us with many new metrics to characterize the social fine-structure of populations and, therefore, with an opportunity to gain an understanding of the role that different personalities play in groups, communities and populations regarding information or disease transmission or in terms of cooperation and policing of social conflicts. The network position of an individual is largely a consequence of its interactive strategies. However, the network position can also shape an individual's experiences (especially in the case of juveniles) and therefore can influence the way in which it interacts with others in future. Finally, over evolutionary time, the social fine-structure of animal populations (as quantified by social network analysis) can have important consequences for the evolution of personalities—an approach that goes beyond the conventional game-theoretic analyses that assumed random mixing of individuals in populations.
Abstract.
Kelley JL, Morrell LJ, Inskip C, Krause J, Croft DP (2011). Predation risk shapes social networks in fission-fusion populations.
PLoS-One,
6(8) Full text.
Ioannou CC, Couzin ID, James R, Croft DP, Krause J (2011). Social Organisation and Information Transfer in Schooling Fish. In (Ed) Fish Cognition and Behavior, 217-239.
Brask JB, Croft DP, Thompson K, Dabelsteen T, Darden S (2011). Social preferences based on sexual attractiveness: a female strategy to reduce male sexual attention.
Proc Biol Sci,
279, 1748-1753.
Abstract:
Social preferences based on sexual attractiveness: a female strategy to reduce male sexual attention
Male sexual harassment of females is common across sexually reproducing species and can result in fitness costs to females. We hypothesized that females can reduce unwanted male attention by constructing a social niche where their female associates are more sexually attractive than themselves, thus influencing the decision-making of males to their advantage. We tested this hypothesis in the Trinidadian guppy (Poecilia reticulata), a species with high levels of male sexual harassment. First, we confirmed that non-receptive females were harassed less when they were paired with a more sexually attractive (receptive) female than with another non-receptive female. We then found that, indeed, females exploit this as a strategy to reduce sexual harassment; non-receptive females actively preferred to associate with receptive over non-receptive females. Importantly, when given access only to chemosensory cues, non-receptive females still showed this preference, suggesting that they use information from chemical cues to assess the sexual attractiveness of potential female partners. Receptive females in contrast showed no such preferences. Our results demonstrate that females can decrease male harassment by associating with females that are more sexually attractive than themselves and that they perform active partner choices based on this relative attractiveness. We propose that this strategy is likely to represent an important pathway by which females can construct social niches that influence the decision-making of others to their advantage; in this case, to reduce the sexual harassment they experience.
Abstract.
2010
Piyapong C, Krause J, Chapman BB, Ramnarine IW, Louca V, Croft DP (2010). Sex matters: a social context to boldness in guppies (Poecilia reticulata).
Behavioral Ecology,
21(1), 3-8.
Abstract:
Sex matters: a social context to boldness in guppies (Poecilia reticulata)
Boldness is a key element of behavioral variation in animals. Many studies have shown variation between individuals in their propensity to take risks across a wide range of taxa, yet surprisingly few studies have investigated the importance of social context in influencing an animal's boldness. Here, we focus on the role that the sex composition of a social group plays in individual boldness in a sexually dimorphic species, the Trinidadian guppy (Poecilia reticulata). We predict that after exposure to a simulated aerial predator, male guppies should be bolder in the presence of females compared with males to maximize their mating opportunities. Furthermore, we predict that female guppies will adopt riskier behavior when shoaling with males in an effort to avoid sexual harassment. Using a model avian predator, we tested these hypotheses and found evidence to support our second prediction but not our first. Specifically, we found that male guppies returned to movement more rapidly after a fright response when shoaling with males than with females. Female focal fish in contrast returned to movement significantly quicker when shoaling with males than females. Also, we found a significant correlation in boldness across social contexts (a behavioral syndrome) in male but not female fish. This study highlights the importance of social context for individual boldness and suggests that for risk-averse behavior in social, sexually dimorphic species, sex matters.
Abstract.
Jones KA, Croft DP, Ramnarine IW, Godin JGJ (2010). Size-assortative shoaling in the guppy (Poecilia reticulata): the role of active choice.
Ethology,
116(2), 147-154.
Abstract:
Size-assortative shoaling in the guppy (Poecilia reticulata): the role of active choice
Many fish species exhibit size-assortative shoaling, which is often thought to be driven by predation risk. Recent fieldwork has revealed that guppies (Poecilia reticulata) are more size assorted in high-predation populations than in low-predation ones. However, size assortment does nonetheless occur in some low-predation populations, suggesting that predation is unlikely the sole driving force behind size-assortment. Here, we investigated in the laboratory the potential role of active choice in size-assortative shoaling in wild-caught female guppies originating from two populations of the same river system in Trinidad. Small or large focal females from each population were offered a binary choice of shoaling with either four small female conspecifics or four large ones. Observed shoaling preferences depended on the body size of the focal fish, suggesting phenotype-mediated conflict over group composition. Large focal fish preferred to shoal with the size-matched stimulus shoal of large fish. In contrast, small focal fish did not shoal assortatively but also preferred to shoal with larger females. Our results suggest that size-assortative shoaling in female guppies is likely to be due to factors other than active choice, such as habitat segregation and sexual harassment. © 2010 Blackwell Verlag GmbH.
Abstract.
2009
Croft DP, Krause J, Darden SK, Ramnarine IW, Faria JJ, James R (2009). Behavioural trait assortment in a social network: Patterns and implications.
Behavioral Ecology and Sociobiology,
63(10), 1495-1503.
Abstract:
Behavioural trait assortment in a social network: Patterns and implications
The social fine structure of a population plays a central role in ecological and evolutionary processes. Whilst many studies have investigated how morphological traits such as size affect social structure of populations, comparatively little is known about the influence of behaviours such as boldness and shyness. Using information on social interactions in a wild population of Trinidadian guppies (Poecilia reticulata), we construct a social network. For each individual in the network, we quantify its behavioural phenotype using two measures of boldness, predator inspection tendency, a repeatable and reliably measured behaviour well studied in the context of co-operation, and shoaling tendency. We observe striking heterogeneity in contact patterns, with strong ties being positively assorted and weak ties negatively assorted by our measured behavioural traits. Moreover, shy fish had more network connections than bold fish and these were on average stronger. In other words, social fine structure is strongly influenced by behavioural trait. We assert that such structure will have implications for the outcome of selection on behavioural traits and we speculate that the observed positive assortment may act as an amplifier of selection contributing to the maintenance of co-operation during predator inspection. © Springer-Verlag 2009.
Abstract.
Full text.
Shorrocks B, Croft DP (2009). Necks and networks: a preliminary study of population structure in the reticulated giraffe (Giraffa camelopardalis reticulata de Winston).
African Journal of Ecology,
47(3), 374-381.
Abstract:
Necks and networks: a preliminary study of population structure in the reticulated giraffe (Giraffa camelopardalis reticulata de Winston)
This paper describes a method of scoring the neck pattern of reticulated giraffes as a simple code that can be searched for in an Excel spreadsheet. This enables several hundred individual giraffe to be recognized and repeatedly found within a database. Possible sources of error are described and quantified. Data on group size, dispersal within groups and social network patterns are described. The latter is facilitated using Ucinet 6.85 for Windows, a software package that helps to visualize and analyse such networks. © 2009 Blackwell Publishing Ltd.
Abstract.
James R, Croft DP, Krause J (2009). Potential banana skins in animal social network analysis.
Behavioral Ecology and Sociobiology,
63(7), 989-997.
Abstract:
Potential banana skins in animal social network analysis
Social network analysis is an increasingly popular tool for the study of the fine-scale and global social structure of animals. It has attracted particular attention by those attempting to unravel social structure in fission-fusion populations. It is clear that the social network approach offers some exciting opportunities for gaining new insights into social systems. However, some of the practices which are currently being used in the animal social networks literature are at worst questionable and at best over-enthusiastic. We highlight some of the areas of method, analysis and interpretation in which greater care may be needed in order to ensure that the biology we extract from our networks is robust. In particular, we suggest that more attention should be given to whether relational data are representative, the potential effect of observational errors and the choice and use of statistical tests. The importance of replication and manipulation must not be forgotten, and the interpretation of results requires care. © 2009 Springer-Verlag.
Abstract.
Croft DP, Darden SK, Ruxton GD (2009). Predation risk as a driving force for phenotypic assortment: a cross-population comparison.
Proc Biol Sci,
276(1663), 1899-1904.
Abstract:
Predation risk as a driving force for phenotypic assortment: a cross-population comparison.
Frequency-dependent predation has been proposed as a general mechanism driving the phenotypic assortment of social groups via the 'oddity effect', which occurs when the presence of odd individuals in a group allows a predator to fixate on a single prey item, increasing the predator's attack-to-kill ratio. However, the generality of the oddity effect has been debated and, previously, there has not been an ecological assessment of the role of predation risk in driving the phenotypic assortment of social groups. Here, we compare the levels of body length assortment of social groups between populations of the Trinidadian guppy (Poecilia reticulata) that experience differences in predation risk. As predicted by the oddity effect hypothesis, we observe phenotypic assortment by body length to be greater under high predation risk. However, we found that a number of low-predation populations were also significantly assorted by body length, suggesting that other mechanisms may have a role to play.
Abstract.
Author URL.
Full text.
Dyer JRG, Croft DP, Morrell LJ, Krause J (2009). Shoal composition determines foraging success in the guppy.
Behavioral Ecology,
20(1), 165-171.
Abstract:
Shoal composition determines foraging success in the guppy
The composition of an animal group can impact greatly on the survival and success of its individual members. Much recent work has concentrated on behavioral variation within animal populations along the bold/shy continuum. Here, we screened individual guppies, Poecilia reticulata, for boldness using an overhead fright stimulus. We created groups consisting of 4 bold individuals (bold shoals), 4 shy individuals (shy shoals), or 2 bold and 2 shy individuals (mixed shoals). The performance of these different shoal types was then tested in a novel foraging scenario. We found that both bold and mixed shoals approached a novel feeder in less time than shy shoals. Interestingly, we found that more fish from mixed shoals fed than in either bold or shy shoals. We suggest that this can be explained by the fact that nearly all the cases where one fish was followed into the feeder by another occurred within mixed shoals and that it was almost always a shy fish following a bold one. These results suggest clear foraging benefits to shy individuals through associating with bold ones. Surprisingly, our results also suggest potential foraging benefits to bold individuals through associating with shy individuals. This study highlights a possible mechanism by which interindividual variation in behavioral types is maintained in a population. © the Author 2008. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved.
Abstract.
Darden SK, James R, Ramnarine IW, Croft DP (2009). Social implications of the battle of the sexes: sexual harassment disrupts female sociality and social recognition.
Proc Biol Sci,
276(1667), 2651-2656.
Abstract:
Social implications of the battle of the sexes: sexual harassment disrupts female sociality and social recognition.
Across sexually reproducing species, males and females are in conflict over the control of reproduction. At the heart of this conflict in a number of taxa is male harassment of females for mating opportunities and female strategies to avoid this harassment. One neglected consequence that may result from sexual harassment is the disruption of important social associations. Here, we experimentally manipulate the degree of sexual harassment that wild female guppies (Poecilia reticulata) experience by establishing replicated, semi-natural pools with different population sex ratios. We quantify the effects of sexual harassment on female social structure and the development of social recognition among females. When exposed to sexual harassment, we found that females had more disparate social networks with limited repeated interactions when compared to females that did not experience male harassment. Furthermore, females that did not experience harassment developed social recognition with familiar individuals over an 8-day period, whereas females that experienced harassment did not, an effect we suggest is due to disruption of association patterns. These results show that social network structure and social recognition can be affected by sexual harassment, an effect that will be relevant across taxonomic groups and that we predict will have fitness consequences for females.
Abstract.
Author URL.
Full text.
Guttridge TL, Gruber SH, Gledhill KS, Croft DP, Sims DW, Krause J (2009). Social preferences of juvenile lemon sharks, Negaprion brevirostris.
Animal Behaviour,
78(2), 543-548.
Abstract:
Social preferences of juvenile lemon sharks, Negaprion brevirostris
Group living in sharks is a widespread phenomenon but relatively little is known about the composition and organization of these groups. In binary choice field experiments juvenile lemon sharks were attracted to conspecifics presumably to form groups. Experiments investigating size assortment preferences indicated that lemon sharks aged 2-3 years (but not 0-1 years) preferred to spend more time with a group of size-matched individuals than unmatched ones. Furthermore, in species association tests lemon sharks spent significantly more time associating with conspecifics than with a sympatric heterospecific, the nurse shark, Ginglymostoma cirratum. These findings enhance our knowledge of group-joining decisions in sharks indicating that active mechanisms can play a role in the formation and composition of shark groups. © 2009 the Association for the Study of Animal Behaviour.
Abstract.
2008
Morrell LJ, Croft DP, Dyer JRG, Chapman BB, Kelley JL, Laland KN, Krause J (2008). Association patterns and foraging behaviour in natural and artificial guppy shoals.
Animal Behaviour,
76(3), 855-864.
Abstract:
Association patterns and foraging behaviour in natural and artificial guppy shoals
Animal groups are often nonrandom assemblages of individuals that tend to be assorted by factors such as sex, body size, relatedness and familiarity. Laboratory studies using fish have shown that familiarity among shoal members confers a number of benefits to individuals, such as increased foraging success. However, it is unclear whether fish in natural shoals obtain these benefits through association with familiars. We investigated whether naturally occurring shoals of guppies, Poecilia reticulata, are more adept at learning a novel foraging task than artificial (in which we selected shoal members randomly) shoals. We used social network analysis to compare the structures of natural and artificial shoals and examined whether shoal organization predicts patterns of foraging behaviour. Fish in natural shoals benefited from increased success in the novel foraging task compared with fish in artificial shoals. Individuals in natural shoals showed a reduced latency to approach the novel feeder, followed more and formed smaller subgroups compared to artificial shoals. Our findings show that fish in natural shoals do gain foraging benefits and that this may be facilitated by a reduced perception of risk among familiarized individuals and/or enhanced social learning mediated by following other individuals and small group sizes. Although the structure of shoals was stable over time, we found no direct relationship between shoal social structure and patterns of foraging behaviour. © 2008 the Association for the Study of Animal Behaviour.
Abstract.
Dyer JRG, Ioannou CC, Morrell LJ, Croft DP, Couzin ID, Waters DA, Krause J (2008). Consensus decision making in human crowds.
Animal Behaviour,
75(2), 461-470.
Abstract:
Consensus decision making in human crowds
In groups of animals only a small proportion of individuals may possess particular information, such as a migration route or the direction to a resource. Individuals may differ in preferred direction resulting in conflicts of interest and, therefore, consensus decisions may have to be made to prevent the group from splitting. Recent theoretical work has shown how leadership and consensus decision making can occur without active signalling or individual recognition. Here we test these predictions experimentally using humans. We found that a small informed minority could guide a group of naïve individuals to a target without verbal communication or obvious signalling. Both the time to target and deviation from target were decreased by the presence of informed individuals. When conflicting directional information was given to different group members, the time taken to reach the target was not significantly increased; suggesting that consensus decision making in conflict situations is possible, and highly efficient. Where there was imbalance in the number of informed individuals with conflicting information, the majority dictated group direction. Our results also suggest that the spatial starting position of informed individuals influences group motion, which has implications in terms of crowd control and planning for evacuations. © 2007 the Association for the Study of Animal Behaviour.
Abstract.
Thomas POR, Croft DP, Morrell LJ, Davis A, Faria JJ, Dyer JRG, Piyapong C, Ramnarine I, Ruxton GD, Krause J, et al (2008). Does defection during predator inspection affect social structure in wild shoals of guppies?.
Animal Behaviour,
75(1), 43-53.
Abstract:
Does defection during predator inspection affect social structure in wild shoals of guppies?
Reciprocal altruism has been proposed as a possible mechanism for the evolution of cooperative behaviour. However, very few investigations have tested predictions of reciprocity in wild animal populations. In the current investigation we simulated defection during predator inspection in a wild population of guppies, Poecilia reticulata. Two experiments were run: the first simulating defection during a single exposure to a predator and the second during multiple exposures to a predator. We then compared subsequent social and cooperative interactions with those observed prior to the treatments. From theory and previous experiments on cooperation and reciprocity, we predicted that defection would result in a reduction in social and cooperative interactions during subsequent predator inspections. However, our experiments did not find any effect of simulated defection(s) on the subsequent social structure, or on patterns of predator inspection behaviour. We discuss the potential reasons for the observed results and suggest future directions for research to address mechanisms underpinning the nature of cooperative interactions during predator inspection. © 2007.
Abstract.
Croft DP, James R, Krause J (2008). Exploring Animal Social Networks. Princetown, NJ, Princetown University Press.
Krause J, Ward AJW, James R, Croft DP (2008). Group living and social networks. In C.Magnhagen, V.Braithwaite, E.Forsgren, Kapoor & BG (eds). In Magnhagen C, Braithwaite V, Forsgren E, Kapoor BG (Eds.) Fish behaviour.
Krause J, Ward AJW, James R, Croft DP (2008). Group-living and social networks. In (Ed)
Fish Behaviour, 485-498.
Abstract:
Group-living and social networks
Abstract.
Croft D (2008). How far will females go to avoid sexual harassment?.
Planet Earth(AUTUMN).
Abstract:
How far will females go to avoid sexual harassment?
The guppies, live-bearer tropical fish, are the ideal species for studying fish sexual harassment. Usually, male guppies tend to compete with other males for mating opportunities. They use their brightly colored patterns to attract females, but if females do not accept the courtship displays, males will often attempt to sneak a mating with her when she is not looking. However, this "dress to impress" characteristic work negatively with male guppies, as they also attract predators. The study conducted suggest that females occupy areas of high-predation risk, trading off increased predation threat for reduced sexual harrassment.
Abstract.
Darden SK, Croft DP (2008). Male harassment drives females to alter habitat use and leads to segregation of the sexes.
Biol Lett,
4(5), 449-451.
Abstract:
Male harassment drives females to alter habitat use and leads to segregation of the sexes.
Sexual conflict is ubiquitous across taxa. It often results in male harassment of females for mating opportunities that are costly for females, in some cases reducing reproductive success and increasing mortality. One strategy that females may employ to avoid sexual harassment is to segregate spatially from males. In fact, we do find sexual segregation in habitat use in species that have high levels of sexual conflict; however, the role of sexual harassment in driving such segregation remains poorly understood. Here, we demonstrate experimentally in a population of wild Trinidadian guppies Poecilia reticulata that male sexual harassment drives females into habitats that they otherwise do not prefer to occupy. In support of the social factors hypothesis for sexual segregation, which states that social factors such as harassment drive sexual segregation, this female behaviour leads to segregation of the sexes. In the presence of males, females actively select areas of high predation risk, but low male presence, and thus trade off increased predation risk against reduced sexual harassment.
Abstract.
Author URL.
Botham MS, Hayward RK, Morrell LJ, Croft DP, Ward JR, Ramnarine I, Krause J (2008). Risk-sensitive antipredator behavior in the Trinidadian guppy, Poecilia reticulata.
Ecology,
89(11), 3174-3185.
Abstract:
Risk-sensitive antipredator behavior in the Trinidadian guppy, Poecilia reticulata
The comparative approach has become a powerful tool for understanding how predation has shaped prey behavior. In this study we recorded the occurrence of common aquatic predator species and their densities in seven natural populations of Trinidadian guppies, Poecilia reticulata. We then exposed shoals of guppies from each of these populations to a series of predator treatments. Predator treatments differed in the species of predator used (pike cichlids, Crenicichla frenata; rivulus, Rivulus hartii; and freshwater prawns, Macro-brachium carcinus) and thus in the level of risk posed. We recorded the antipredator responses of guppies in each of these predator treatments. The strength of antipredator behavior shown by guppies was affected by both the type of predator they were exposed to and the level of predation risk they experienced naturally in the wild. Importantly, we found that guppies from high-risk populations showed a heightened response, compared to those from lower risk populations, only when exposed to the predator species that posed the greatest risk. Our results show the importance of individual predator species in shaping the behavioral traits of prey species at the population level. This has implications for prey movement between habitats that are geographically close but differ greatly in predator fauna. © 2008 by the Ecological Society of America.
Abstract.
2007
Piyapong C, Morrell LJ, Croft DP, Dyer JRG, Ioannou CC, Krause J (2007). A cost of leadership in human groups.
Ethology,
113(9), 821-824.
Abstract:
A cost of leadership in human groups
Group living is the result of a dynamic trade-off between associated costs and benefits. However, these costs and benefits are not necessarily distributed equally across different spatial positions of groups which may result in different fitness returns for individuals occupying different positions in groups. Here we consider whether leadership of a group during a navigation task in humans may have a specific cost associated with it. Pairs of students performed a counting task whilst walking through two obstacle courses, once as leader and once as follower. We found that leaders made significantly more errors in the counting task than followers suggesting that there is an attention cost associated with leadership/navigation behaviour. © 2007 the Authors.
Abstract.
Morrell LJ, Hunt KL, Croft DP, Krause J (2007). Diet, familiarity and shoaling decisions in guppies.
Animal Behaviour,
74(2), 311-319.
Abstract:
Diet, familiarity and shoaling decisions in guppies
Animals are known to derive benefits from associating with familiar individuals, and familiarity is important in the structuring of animal groups. In fish, individuals are known to shoal preferentially with others they have previously spent time with (familiar individuals). One mechanism used in fish shoaling decisions may be local olfactory cues; individuals prefer to shoal with conspecifics that have experienced a similar recent environment to themselves. We investigated the role of diet-based cues in the social decisions of domestic guppies, Poecilia reticulata. Diet strongly affected shoaling decisions. Fish fed a bloodworm diet preferred to shoal with familiar individuals and with those that had been fed a similar diet. Flake food-fed fish, on the other hand, preferentially associated with fish fed on bloodworm, and showed a strong preference for unfamiliar fish when both shoals were fed flake food. These results suggest that several factors may interact to influence shoaling decisions. Bloodworm-fed fish also strongly preferred the olfactory cues of their own diet to flake food odour whereas flake food-fed fish showed no preference for either odour type. Fish on bloodworm diets, however, grew faster. We suggest potential explanations for the flake food-fed individuals' preference for unfamiliar fish. © 2007 the Association for the Study of Animal Behaviour.
Abstract.
Krause J, Croft DP, James R (2007). Social network theory in the behavioural sciences: Potential applications.
Behavioral Ecology and Sociobiology,
62(1), 15-27.
Abstract:
Social network theory in the behavioural sciences: Potential applications
Social network theory has made major contributions to our understanding of human social organisation but has found relatively little application in the field of animal behaviour. In this review, we identify several broad research areas where the networks approach could greatly enhance our understanding of social patterns and processes in animals. The network theory provides a quantitative framework that can be used to characterise social structure both at the level of the individual and the population. These novel quantitative variables may provide a new tool in addressing key questions in behavioural ecology particularly in relation to the evolution of social organisation and the impact of social structure on evolutionary processes. For example, network measures could be used to compare social networks of different species or populations making full use of the comparative approach. However, the networks approach can in principle go beyond identifying structural patterns and also can help with the understanding of processes within animal populations such as disease transmission and information transfer. Finally, understanding the pattern of interactions in the network (i.e. who is connected to whom) can also shed some light on the evolution of behavioural strategies. © 2007 Springer-Verlag.
Abstract.
Croft DP, Griffiths SW, Magurran AE, Krause J (2007). The Influence of Reproductive Behaviour on the Social Organisation of Shoaling Fish. In Rocha MJ, Arukwe A, Kapoor BG (Eds.) Fish Reproduction.
2006
Krause J, James R, Croft DP (2006). Analyse sozialer Netzwerke. In (Ed) Methoden der Verhaltensbiologie, 148-152.
Croft DP, Morrell LJ, Wade AS, Piyapong C, Ioannou CC, Dyer JRG, Chapman BB, Wong Y, Krause J (2006). Predation risk as a driving force for sexual segregation: a cross-population comparison.
Am Nat,
167(6), 867-878.
Abstract:
Predation risk as a driving force for sexual segregation: a cross-population comparison.
Sexual segregation is widespread throughout the animal kingdom. Although a number of hypotheses have been proposed to account for observed patterns, the generality of the mechanisms remains debated. One possible reason for this is the focus on segregation patterns in large mammals such as ungulates, where the majority of studies are descriptions of a single population. Here, we present the results of a cross‐population comparison of patterns of sexual segregation in the Trinidadian guppy, Poecilia reticulata. We relate observed patterns to experimental quantification of predation risk and sexual harassment of females by males in eight populations. We find that the degree of segregation increases with predation risk, with deeper waters becoming increasingly female biased. Furthermore, we observed that levels of male harassment are lower in deeper water but only in those rivers that contain major guppy predators. We conclude that sexual segregation in guppies is consistent with the predation risk hypothesis: sexual segregation results from a combination of predation risk driving males (the more vulnerable sex) into less risky habitats and females gaining benefits of reduced sexual harassment by remaining in high‐predation environments.
Abstract.
Author URL.
Croft DP, Krause J, James R (2006). Predator avoidance and reproductive strategies: Predation risk as a driving factor for size assortative shoaling and its implications for sexual segregation in fish. In (Ed)
Sexual Segregation in Vertebrates: Ecology of the Two Sexes, 115-126.
Abstract:
Predator avoidance and reproductive strategies: Predation risk as a driving factor for size assortative shoaling and its implications for sexual segregation in fish
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Couzin ID, James R, Croft DP, Krause J (2006). Social organization and information transfer in schooling fish. In Brown C, Laland KN, Krause J (Eds.) Fish Cognition and Behaviour, Cambridge: Blackwell Publishing.
Wright D, Ward AJW, Croft DP, Krause J (2006). Social organization, grouping, and domestication in fish.
Zebrafish,
3(2), 141-155.
Abstract:
Social organization, grouping, and domestication in fish
The zebrafish (Danio rerio) is now established as one of the pre-eminent model vertebrate study animals in biology, providing an excellent opportunity to integrate the fields of genetics and behavioral ecology. Considerable attention has been paid to the social organization of animals and the study of zebrafish in this context allows behavioral geneticists to gain an insight into this fundamentally important field. This paper reviews the literature on the social organization of fish, with special reference to the zebrafish. The mechanisms and functions of social behavior in fish and the current understanding of the behavioral genetics of these are discussed. Finally, the impact of domestication on the expression of wild-type behavior patterns in laboratory fish is considered. © Mary Ann Liebert, Inc.
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Croft DP, James R, Thomas POR, Hathaway C, Mawdsley D, Laland KN, Krause J (2006). Social structure and co-operative interactions in a wild population of guppies (Poecilia reticulata).
Behavioral Ecology and Sociobiology,
59(5), 644-650.
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Social structure and co-operative interactions in a wild population of guppies (Poecilia reticulata)
In contrast to the substantial number of theoretical papers that have examined the mechanisms by which cooperation may evolve, very few studies have investigated patterns of co-operation in natural animal populations. In the current study, we use a novel approach, social network analysis, to investigate the structure of co-operative interactions in the context of predator inspection in a wild population of guppies (Poecilia reticulata). Female guppies showed social preferences for stable partners, fulfilling a key assumption made by models of reciprocity. In the laboratory, wild female guppies disproportionately engaged in predator inspection with others with whom they had strong social associations. Furthermore, pairs of fish that frequently engaged in predator inspection did so in a particularly co-operative way, potentially reducing costs associated with predator inspection. Taken together, these results provide evidence for assortative interactions forming the basis of co-operation during predator inspection in a natural fish population. The occurrence of highly interconnected social networks between stable partners suggests the existence of co-operation networks in free-ranging populations of the guppy. © Springer-Verlag 2005.
Abstract.
Krause J, James R, Croft DP (2006). Soziale Netzwerke bei Tieren. In Naguib M (Ed) Methoden der Verhaltensbiologie Heidelberg, Springer-Verlag.
2005
Croft DP, James R, Ward AJW, Botham MS, Mawdsley D, Krause J (2005). Assortative interactions and social networks in fish.
Oecologia,
143(2), 211-219.
Abstract:
Assortative interactions and social networks in fish.
The mechanisms underpinning the structure of social networks in multiple fish populations were investigated. To our knowledge this is the first study to provide replication of social networks and therefore probably the first that allows general conclusions to be drawn. The social networks were all found to have a non-random structure and exhibited 'social cliquishness'. A number of factors were observed to contribute to this structuring. Firstly, social network structure was influenced by body length and shoaling tendency, with individuals interacting more frequently with conspecifics of similar body length and shoaling tendency. Secondly, individuals with many social contacts were found to interact with each other more often than with other conspecifics, a phenomenon known as a 'positive degree correlation'. Finally, repeated interactions between pairs of individuals occurred within the networks more often than expected by random interactions. The observed network structures will have ecological and evolutionary implications. For example, the occurrence of positive degree correlations suggests the possibility that pathogens and information (that are socially transmitted) could spread very fast within the populations. Furthermore, the occurrence of repeated interactions between pairs of individuals fulfils an important pre-requisite for the evolution of reciprocal altruism.
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Croft DP, James R, Krause J (2005). Predator avoidance as a factor for size assortative shoaling and its implications for sex segregation in fish. In Ruckstuhl K, Neuhaus P (Eds.) Sexual segregation in vertebrates: ecology of the two sexes, Cambridge University Press.
2004
Croft DP, Arrowsmith BJ, Webster M, Krause J (2004). Intra-sexual preferences for familiar fish in male guppies.
Journal of Fish Biology,
64(1), 279-283.
Abstract:
Intra-sexual preferences for familiar fish in male guppies
Male guppies Poecilia reticulata were observed to develop shoaling preferences for familiar males over a 12 day period, at which time they showed a clear preference for familiar over non-familiar males. © 2004 the Fisheries Society of the British Isles.
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Croft DP, Botham MS, Krause J (2004). Is sexual segregation in the guppy, Poecilia reticulata, consistent with the predation risk hypothesis?.
Environmental Biology of Fishes,
71(2), 127-133.
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Is sexual segregation in the guppy, Poecilia reticulata, consistent with the predation risk hypothesis?
We examined the importance of sex differences in predation risk in generating sexual segregation in the guppy, Poecilia reticulata. We hypothesised that sex differences in predation risk will result in habitat segregation and ultimately social segregation of the sexes, with the more vulnerable sex (males in this case) using safer habitats. In accordance with the predation risk hypothesis we observed sexual segregation in a population associated with high but not low predation risk. Under high predation risk we observed a larger proportion of males in shallow marginal habitats resulting in habitat segregation and ultimately social segregation of the sexes. Furthermore, habitat segregation by sex was associated with habitat segregation by body length with shoals in deeper water having a larger mean body length. Shoaling fish species have been key models in investigating group living, and further research directed towards understanding sexual segregation in other fish species would be valuable.
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Croft DP, Krause J, James R (2004). Social networks in the guppy (Poecilia reticulata).
Proc Biol Sci,
271 Suppl 6, S516-S519.
Abstract:
Social networks in the guppy (Poecilia reticulata).
Social network theory is used to elicit details of the social structure of a population of free-ranging guppies, Poecilia reticulata. They were found to have a complex and highly structured social network, which exhibited characteristics consistent with the 'small world' phenomenon. Stable partner associations between individuals were observed, a finding that fulfils the basic prerequisite for the evolution of reciprocal altruism. The findings are discussed in relation to the ecology and evolution of the wild population, highlighting the potential application of network theory to social associations in animals.
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2003
Croft DP, Arrowsmith BJ, Bielby J, Skinner K, White E, Couzin ID, Magurran AE, Ramnarine I, Krause J (2003). Mechanisms underlying shoal composition in the Trinidadian guppy, Poecilia reticulata.
Oikos,
100(3), 429-438.
Abstract:
Mechanisms underlying shoal composition in the Trinidadian guppy, Poecilia reticulata
Free-ranging groups are frequently assorted by phenotypic characters. However, very little is known about the underlying processes that determine this structuring. In this study, we investigate the mechanisms underlying the phenotypic composition of shoals of guppies (Poecilia reticulata) in a high-predation stream in Trinidad's Northern Mountain Range. We collected 57 entire wild shoals, which were strongly assorted by body length. Shoal encounters staged within an experimental arena showed shoal fission (but not fusion) events to be an important mechanism in generating phenotypic assortment. In the wild, fission and fusion between guppy shoals occurred extremely frequently and thus are unlikely to constrain the opportunities for shoal assortment. However, fission and fusion processes occur under the restrictions imposed by the distribution of individuals within the environment. We observed size specific segregation within the habitat in three dimensions, providing a passive mechanism that contributes to the maintenance of the observed homogeneity of group composition. Furthermore sex differences were found in social behaviour. Individual male guppies switched between shoals more frequently than females and left a shoal more often than females. We argue that shoal composition is determined by habitat segregation on a medium spatial scale and by fission/fusion processes on a small spatial scale (with sex-specific shoal dynamics adding a additional layer of complexity).
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Croft DP, Albanese B, Arrowsmith BJ, Botham M, Webster M, Krause J (2003). Sex-biased movement in the guppy (Poecilia reticulata).
Oecologia,
137(1), 62-68.
Abstract:
Sex-biased movement in the guppy (Poecilia reticulata).
The movement strategies of birds and mammals are often closely linked to their mating system, but few studies have examined the relationship between mating systems and movement in fishes. We examined the movement patterns of the guppy ( Poecilia reticulata) in the Arima river of Trinidad and predicted that sexual asymmetry in reproductive investment would result in male-biased movement. Since male guppies maximize their reproductive success by mating with as many different females as possible, there should be strong selection for males to move in search of mates. In agreement with our prediction, the percentage of fish that emigrated from release pools was higher for males than females (27.3% vs. 6.9%, respectively). Sex ratio was highly variable among pools and may influence a male's decision to emigrate or continue moving. We also detected a positive relationship between body length and the probability of emigration for males and a significant bias for upstream movement by males. Among the few females that did emigrate, a positive correlation was observed between body length and distance moved. Sex-biased movement appears to be related to mating systems in fishes, but the evidence is very limited. Given the implications for ecology, evolution, and conservation, future studies should explicitly address the influence of sex and mating systems on movement patterns.
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Croft DP, Krause J, Couzin ID, Pitcher TJ (2003). When fish shoals meet: Outcomes for evolution and fisheries.
Fish and Fisheries,
4(2), 138-146.
Abstract:
When fish shoals meet: Outcomes for evolution and fisheries
The mechanisms underlying the social structure of free-ranging fish shoals have received little attention in comparison to functional studies on shoaling. Recently, however, a number of investigations, both in the marine and in the freshwater environment, have begun to address the underlying mechanisms by concentrating on interactions between free-ranging shoals. The rates of shoal encounters can influence the opportunities for individual assortment by phenotype and selection of shoal size: act as a constraint on the observed patterns of shoal structure by restricting individual choice behaviour and were found to be high in several small freshwater species (where intershoal distances were small), but lower in marine species where shoals were more dispersed. The duration of encounters may play a role in that it affects both the time available for assessment (of the encountered shoal) as well as that for exchange of individuals. Scarce published information on the outcome of shoal encounters suggests that the outcome of shoal encounters is influenced by shoal composition but not by shoal size. Individual behaviour may have evolved to maintain shoal size when shoals encounter, but when fish populations are depleted by fishing, this trait can exacerbate range and stock collapse. Furthermore, an understanding of the dynamics of shoal encounters has important consequences for the evolution of reciprocal altruism and the transmission of information through social learning within populations. Finally, information on encounter rates between shoals and the number of individuals that are exchanged on such occasions could be important for making predictions about the spread of disease through fish populations.
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2001
Hoare DJ, Ward AJW, Couzin ID, Croft DP, Krause J (2001). A grid-net technique for the analysis of fish positions within free-ranging shoals.
Journal of Fish Biology,
59(6), 1667-1672.
Abstract:
A grid-net technique for the analysis of fish positions within free-ranging shoals
The design and operation of a grid-net are described, which allows the capture of entire shoals of wild fish and preserves information about the two-dimensional structure of shoals and the spatial positions of individual fish within the shoal. This simple technique facilitates investigation of several aspects of individual differences in fish shoaling behaviour in the wild for the first time. © 2001 the Fisheries Society of the British Isles.
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2000
Krause J, Hoare DJ, Croft D, Lawrence J, Ward A, Ruxton GD, Godin JG, James R (2000). Fish shoal composition: mechanisms and constraints.
Proc Biol Sci,
267(1456), 2011-2017.
Abstract:
Fish shoal composition: mechanisms and constraints.
Observations were made on three fish species (banded killifish (Fundulus diaphanus), golden shiner (Notemigonus crysoleucas) and white sucker (Catostomus commersoni)) in a temperate lake (New Brunswick, Canada) in order to investigate the relationship between shoal choice behaviour of individual fishes and shoal composition. Encounters between shoals were observed to take place every 1.1 min per shoal and an encounter lasted 3.7 s on average. The duration of shoal encounters was influenced by shoal size but not by differences between shoals in either body length or species. Conversely, the outcome of shoal encounters (i.e. ences between shoals in either body length or species. Conversely, the outcome of shoal encounters (i.e. whether or not an individual changes shoal) was influenced by body length and species differences but not by shoal size. Together, these results suggest that encounter duration itself is unlikely to have an important influence on encounter outcome. The collection of ten entire fish shoals showed that they were assorted by species and body length. A simulation model demonstrated that individual shoal choice behaviour alone could account for the generation and maintenance of the observed levels of size assortedness of shoals without invoking the existence of other sorting mechanisms such as differential swimming speeds. However, the generation of species assortedness was not predicted by the model. Furthermore, our data suggest that fish density acts as a constraint on shoal choice, influencing both shoal size and composition. This work has implications for studies on information transfer and reciprocal altruism within populations.
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