Publications by year
In Press
Wilde JA, Darden SK, Hart JDA, Weiss MN, Ellis S, Fawcett TW (In Press). Biomimetic robots reveal flexible adjustment of sexual signalling in a wild invertebrate.
Abstract:
Biomimetic robots reveal flexible adjustment of sexual signalling in a wild invertebrate
Sexual signals are often structured in bouts, which can be adjusted in response to changes in the signaller’s physical and social environment. For example, we might expect individuals to adjust their own signalling behaviour in response to changes in the signalling behaviour of rivals, because this can affect their relative attractiveness to potential mates. In this study, we used a biomimetic robot to experimentally manipulate rival waving behaviour in a wild population of fiddler crabs (Afruca tangeri), and investigated whether this leads to changes in the activity and waving behaviour of a focal male. Analysing the focal male’s behaviour using hidden Markov models and linear hurdle models, we found no evidence that the focal male’s waving rate changed in response to changes in the behaviour of the robotic rival. However, bouts of waving lasted longer when the robotic rival was waving at a fast rate. Focal males were also less likely to enter their burrow when the robotic rival was waving, and spent less time in their burrow if they did enter. These results reveal tactical adjustment of behaviour by competing signallers, and highlight the flexible nature of bout-structured sexual displays.
Abstract.
Dimitriadou S, Winberg S, Thörnqvist P-O, Croft D, Darden S (In Press). Brain monoaminergic activity during predator inspection in female Trinidadian guppies (Poecilia reticulata). Behavioural Brain Research
Dimitriadou S, Winberg S, Thörnqvist P-O, Croft DP, Darden SK (In Press). Brain monoaminergic activity during predator inspection in the Trinidadian guppy (<i>Poecilia reticulata</i>).
Abstract:
Brain monoaminergic activity during predator inspection in the Trinidadian guppy (Poecilia reticulata)
AbstractTo 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.List of abbreviations used
Abstract.
Ciftci E, Barreto M, Doyle D, van Breen J, Darden S (In Press). Distancing or drawing together: Sexism and organizational tolerance of sexism impact women’s social relationships at work. European Journal of Social Psychology
Macario A, Darden S, Verbruggen F, Croft D (In Press). Intraspecific variation in inhibitory motor control in guppies, Poecilia reticulata. Journal of Fish Biology
Dimitriadou S, Santos EM, Croft DP, van Aerle R, Ramnarine IW, Filby AL, Darden SK (In Press). Social partner cooperativeness influences brain <i>oxytocin</i> transcription in Trinidadian guppies (<i>Poecilia reticulata</i>).
Abstract:
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.
Darden S-K, James R, Cave JM, Brask JB, Croft DP (In Press). Trinidadian guppies use a social heuristic that can support cooperation among non-kin. Proceedings of the Royal Society B: Biological Sciences
2023
Padget RFB, Fawcett TW, Darden SK (2023). Guppies in large groups cooperate more frequently in an experimental test of the group size paradox.
Proceedings of the Royal Society B: Biological Sciences,
290, 20230790-20230790.
Abstract:
Guppies in large groups cooperate more frequently in an experimental test of the group size paradox
The volunteer’s dilemma, in which a single individual is required to produce a public good, predicts that individuals in larger groups will cooperate less frequently. Mechanistically, this could result from trade-offs between costs associated with volunteering and costs incurred if the public good is not produced (nobody volunteers). During predator inspection, one major contributor to the cost of volunteering is likely increased probability of predation; however, a predator also poses a risk to all individuals if nobody inspects. We tested the prediction that guppies in larger groups will inspect a predator less than those in smaller groups. We also predicted that individuals in larger groups would perceive less threat from the predator stimulus because of the protective benefits of larger groups (e.g. dilution). Contrary to prediction, we found that individuals in large groups inspected more frequently than those in smaller groups, but (as predicted) spent less time in refuges. There was evidence that individuals in intermediate-sized groups made fewest inspections and spent most time in refuges, suggesting that any link between group size, risk and cooperation is not driven by simple dilution. Extensions of theoretical models that capture these dynamics will likely be broadly applicable to risky cooperative behaviour.
Abstract.
Wilde JA, Rodríguez-Muñoz R, Darden SK, Tregenza T, Fawcett TW (2023). Signalling males increase or decrease their calling effort according to the proximity of rivals in a wild cricket.
Animal Behaviour,
203, 53-61.
Abstract:
Signalling males increase or decrease their calling effort according to the proximity of rivals in a wild cricket
Males that employ dynamic courtship displays to attract females may tactically adjust their courtship in response to their social environment. However, we know little about how sexual signals are adjusted in complex natural settings, where individuals are competing for attention against a backdrop of signals from nearby and distant rivals. We investigated this using data from the WildCrickets project, a wild population of field crickets, Gryllus campestris, continuously monitored via CCTV cameras. We used over a million scan samples from 129 males across 51 days to explore how the singing and proximity of other males influenced male singing behaviour. We first quantified the spatial network of the males to understand how the extent of singing overlap is affected by the distance between them, and found a moderate overlap across the whole population, regardless of distance. We then used a finer-grained analysis controlling for the effect of environmental variables. At distances greater than 1 m, we found a stimulatory effect of singing by other males on a focal male's singing behaviour, leading to males singing in the same time intervals. The overlap in singing became weaker as the distance between males increased. Conversely, we found that males were less likely to call when another male was singing very close by (within 1 m), suggesting an inhibitory effect. These findings reveal how, in a dynamic social network in a wild population, males perform fine-scale adjustments to their signalling behaviour in response to signalling by other males both nearby and far away.
Abstract.
2021
Ciftci EE (2021). How gender discrimination influences social ties among women.
Abstract:
How gender discrimination influences social ties among women
In this PhD, we examine how experiences with sexism affect women’s social relationships with other women. We assess the role played by tolerance of sexism in the workplace, including perceptions of tolerance of sexism at the peer-, manager-, and policy-level. Chapter 1 provides a review of the literature on devaluated group members’ responses to stigma on their relationship with other members of their groups and highlight the role of context on the effect of stigma on interpersonal relationships. Chapter 2 reports secondary analyses of existing data to examine the how tolerance of gender devaluation (sexualised harassment and non-sexualised sexism) moderates the impact of sexism on women’s psychological wellbeing. Chapter 3 reports a series of studies with working women, focusing on the effects of perceived peer, leader, and policy tolerance of sexism on women’s affiliation with female co-workers. Chapter 4 describes a pilot study and a laboratory experiment where we orthogonally manipulated exposure to sexism and peer tolerance of sexism. Our results show some inconsistencies but overall support the idea that organizational tolerance of gender devaluation plays an important role in women’s wellbeing and social responses to sexism. We summarize and integrate the findings across the three empirical chapters and discuss implications of theory and practice in Chapter 5.
Abstract.
Dimitriadou S, Santos E, Croft D, van Aerle R, Ramnarine I, Filby A, Darden S (2021). Social partner cooperativeness influences brain <i>oxytocin</i> transcription in Trinidadian guppies (<i>Poecilia reticulata</i>).
Abstract:
Social partner cooperativeness influences brain oxytocin transcription in Trinidadian guppies (Poecilia reticulata)
For 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.
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.
Darden SK, James R, Cave JM, Brask JB, Croft DP (2020). Trinidadian guppies use a social heuristic that can support cooperation among non-kin: Heuristics and real-world cooperation.
Proceedings of the Royal Society B: Biological Sciences,
287(1934).
Abstract:
Trinidadian guppies use a social heuristic that can support cooperation among non-kin: Heuristics and real-world cooperation
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.
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.
Abstract.
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.
ROYAL SOCIETY OPEN SCIENCE,
6(1).
Author URL.
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.
Author URL.
Darden SK, May MK, Boyland NK, Dabelsteen T (2019). Territorial defense in a network: audiences only matter to male fiddler crabs primed for confrontation.
BEHAVIORAL ECOLOGY,
30(2), 336-340.
Author URL.
2018
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.
Author URL.
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.
Heathcote RJP, Darden SK, Franks DW, Ramnarine IW, Croft DP (2017). Fear of predation drives stable and differentiated social relationships in guppies.
Scientific Reports,
7(1).
Abstract:
Fear of predation drives stable and differentiated social relationships in guppies
AbstractSocial 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.
Abstract.
Edenbrow M, Bleakley BH, Darden SK, Tyler CR, Ramnarine IW, Croft DP (2017). The Evolution of Cooperation: Interacting Phenotypes among Social Partners. The American Naturalist, 189(6), 630-643.
2016
Croft DP, Darden SK, Wey TW (2016). Current directions in animal social networks. Current Opinion in Behavioral Sciences, 12, 52-58.
2015
Killen SS, Croft DP, Salin K, Darden SK (2015). 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
Summary
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.
Abstract.
2014
Croft DP, Edenbrow M, Darden S (2014). Assortment in social networks and the evolution of cooperation. In (Ed) Animal Social Networks, Oxford University Press, 13-23.
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.
Darden SK, Watts L (2012). Male sexual harassment alters female social behaviour towards other females.
Biology Letters,
8(2), 186-188.
Abstract:
Male sexual harassment alters female social behaviour towards other females
Male harassment of females to gain mating opportunities is a consequence of an evolutionary conflict of interest between the sexes over reproduction and is common among sexually reproducing species. Male Trinidadian guppies Poecilia reticulata spend a large proportion of their time harassing females for copulations and their presence in female social groups has been shown to disrupt female-female social networks and the propensity for females to develop social recognition based on familiarity. In this study, we investigate the behavioural mechanisms that may lead to this disruption of female sociality. Using two experiments, we test the hypothesis that male presence will directly affect social behaviours expressed by females towards other females in the population. In experiment one, we tested for an effect of male presence on female shoaling behaviour and found that, in the presence of a free-swimming male guppy, females spent shorter amounts of time with other females than when in the presence of a free-swimming female guppy. In experiment two, we tested for an effect of male presence on the incidence of aggressive behaviour among female guppies. When males were present in a shoal, females exhibited increased levels of overall aggression towards other females compared with female only shoals. Our work provides direct evidence that the presence of sexually harassing males alters female-female social behaviour, an effect that we expect will be recurrent across taxonomic groups. © 2011 the Royal Society.
Abstract.
Lebsock AA, Burdett CL, Darden SK, Dabelsteen T, Antolin MF, Crooks KR (2012). Space use and territoriality in swift foxes (Vulpes velox) in northeastern Colorado.
Canadian Journal of Zoology,
90(3), 337-344.
Abstract:
Space use and territoriality in swift foxes (Vulpes velox) in northeastern Colorado
Space use is a fundamental characteristic that informs our knowledge of social relationships and the degree to which individuals are territorial. Until recently, relatively little was known about the spatial ecology and social organization of swift foxes (Vulpesvelox (Say, 1823)). We investigated space use of swift foxes on short grass prairie in northeastern Colorado. Our first objective was to evaluate sizes of seasonal and annual home ranges and core areas of 13 radio-collared swift foxes monitored continuously for 2 years. Our second objective was to compare home-range and core-area overlap of breeding pairs to that of neighboring foxes, including male-male, female-female, and non breeding female-male dyads. Home range size in our study population was among the smallest previously reported for swift foxes. Males tended to have slightly larger home ranges and core areas than females, and home-range size was significantly larger in the breeding season than in both the pup-rearing and the dispersal seasons; sizes of core areas did not differ seasonally. Spatial overlap between breeding pairs was substantial, whereas spatial overlap between neighbors, particularly males, was low, suggesting territoriality.
Abstract.
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
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.
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.
Hebert L, Darden SK, Pedersen BV, Dabelsteen T (2011). Increased DNA amplification success of non-invasive genetic samples by successful removal of inhibitors from faecal samples collected in the field.
Conservation Genetics Resources,
3(1), 41-43.
Abstract:
Increased DNA amplification success of non-invasive genetic samples by successful removal of inhibitors from faecal samples collected in the field
The use of non-invasive genetic sampling (NGS) is becoming increasingly important in the study of wild animal populations. Obtaining DNA from faecal samples is of particular interest because faeces can be collected without deploying sample capture devices. However, PCR amplification of DNA extracted from faeces is problematic because of high concentrations of inhibitors. Here we present a method for increasing the successful application of donor DNA extracted from faecal samples through inhibitor reduction. After standard extraction with a DNA stool kit we used a 'Concentrated Chelex Treatment' (CCT) that increased the amplification success from 31.7 to 61.4% of loci. Our results suggest that darker supernatant and samples with more precipitate contain more inhibitors than lighter samples and samples with little or no precipitate. We expect the use of this technique to have wide applicability within conservation biology for research and management that relies on NGS of wild animal populations. © 2010 Springer Science+Business Media B.V.
Abstract.
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.
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.
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.
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.
2008
Darden SK, Dabelsteen T (2008). Acoustic territorial signalling in a small, socially monogamous canid.
Animal Behaviour,
75(3), 905-912.
Abstract:
Acoustic territorial signalling in a small, socially monogamous canid
Animals that actively defend all or part of their home range for the exclusive use of members of their social group are considered territorial. Defended areas may contain resources such as dens or nests, key foraging sites, or sexual partners that vary in value by season. We investigated territoriality and the function of long-ranging barking sequences in a wild population of swift foxes, Vulpes velox. We monitored space use and barking behaviour and combined this with experimental acoustic playback during the mating season. Mated male foxes used barking sequences mainly inside or close to the boundary of the pair's home range core (50% kernel contour isoline of estimated home range). Similarly, male resident foxes responded more intensely with barking if a playback simulating intrusion by a rival occurred inside of the core compared to outside of it. However, it was common for home range cores to be partly overlapped by neighbouring home ranges and therefore we cannot arbitrarily define 50% home range cores as territories. Still, pair home ranges had areas that were exclusive to the mated pair and their primary and secondary daytime sleeping dens were usually located inside these areas. These results suggest that the barking sequence is used in territorial defence and we conclude that at least male swift foxes are territorial in the mating season and they use a long-ranging acoustic signal in territory defence. © 2007 the Association for the Study of Animal Behaviour.
Abstract.
Darden SK, Steffensen LK, Dabelsteen T (2008). Information transfer among widely spaced individuals: latrines as a basis for communication networks in the swift fox?.
Animal Behaviour,
75(2), 425-432.
Abstract:
Information transfer among widely spaced individuals: latrines as a basis for communication networks in the swift fox?
In species where individuals are widely spaced instantaneous signals cannot readily form the basis of communication networks, that is several individuals within signalling range of each other. However, markings, signals that remain in the environment after the signaller has left, may fulfil this role. In this study, we have investigated the possible function of swift fox, Vulpes velox, latrines, collections of scat, urine and possibly other secretions, in a communication network context. We found that latrines had higher frequencies of occurrence inside the core (defined as the 50% kernel contour) of a pair's home-range when compared with outside the core and in areas of a pair's home-range that overlapped with neighbouring individuals when compared with those areas that did not overlap with neighbours. These were also the two areas where latrines were most likely to reoccur in the next consecutive breeding season. Furthermore, latrines in the exclusive part of a pair's home-range core and latrines in edge area overlap zones had the highest frequency of visits as determined by the rate of faecal depositions. Our interpretation of these results is that latrines possibly have a dual function. That is, they function in territory defence in the exclusive areas of a pair's core and as centres for information exchange in the outer areas of a pair's home-range that overlap with neighbouring foxes. We discuss the possible information content of latrines and the possibility of latrines forming the basis of communication networks in the swift fox. © 2007 the Association for the Study of Animal Behaviour.
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.
Darden SK, Pedersen SB, Larsen ON, Dabelsteen T (2008). Sound transmission at ground level in a short-grass prairie habitat and its implications for long-range communication in the swift fox Vulpes velox.
J Acoust Soc Am,
124(2), 758-766.
Abstract:
Sound transmission at ground level in a short-grass prairie habitat and its implications for long-range communication in the swift fox Vulpes velox.
The acoustic environment of swift foxes Vulpes velox vocalizing close to the ground and the effect of propagation on individual identity information in vocalizations were quantified in a transmission experiment in prairie habitat. Sounds were propagated (0.45 m above the ground) at distances up to 400 m. Effects of transmission were measured on three sound types: synthesized sweeps with 1.3 kHz bandwidths spanning in the range of 0.3-8.0 kHz; single elements of swift fox barking sequences (frequency range of 0.3-4.0 kHz) and complete barking sequences. Synthesized sweeps spanning 0.3-1.6 and 1.2-2.5 kHz propagated the furthest and the latter sweeps exhibited the best transmission properties for long-range propagation. Swift fox barking sequence elements are centered toward the lower end of this frequency range. Nevertheless, measurable individual spectral characteristics of the barking sequence seem to persist to at least 400 m. Individual temporal features were very consistent to at least 400 m. The communication range of the barking sequences is likely to be farther than 400 m and it should be considered a long-ranging vocalization. However, relative to the large home ranges of swift foxes (up to 16 km(2) in the experimental area) the barking sequence probably functions at intermediate distances.
Abstract.
Author URL.
2007
Poesel A, Dabelsteen T, Darden SK, Delhey K, Peters A (2007). Territorial responses of male blue tits, Cyanistes caeruleus, to UV-manipulated neighbours.
Journal of Ornithology,
148(2), 179-187.
Abstract:
Territorial responses of male blue tits, Cyanistes caeruleus, to UV-manipulated neighbours
Multiple phenotypic traits can affect the outcome of interactions among territorial animals. Individuals may use current and previously acquired information on phenotypic traits to assess the competitive ability of opponents and adjust the strength of their response depending on the threat the opponent poses. In birds, colourful plumage and song are widespread phenotypic traits. Recent work has shown that ultraviolet (UV) plumage reflectance may be used by males in assessing an opponent's strength and by females in mate choice. In the present study, we investigated whether and how territorial male blue tits, Cyanistes caeruleus, use previously acquired information from UV reflectance of the crown feathers of neighbours to adjust their response to playback of song of these neighbours simulated to intrude their territory. We compared responses to neighbours with those to unfamiliar strangers with unknown plumage features. We found that subject males with UV-enhanced neighbours responded more strongly to these neighbours than to strangers, i.e. showed more flights, used songs without trill and tended to overlap more songs. Subject males with UV-reduced neighbours gave a lower or similar response to neighbours compared to strangers. This indicates that male blue tits combine previously acquired information about an intruder's plumage with familiarity of its song, and that their response depends on the perceived quality of the neighbour. This study provides evidence that familiarity in combination with multiple signals of quality may influence territorial relations among neighbours. © Dt. Ornithologen-Gesellschaft e.V. 2006.
Abstract.
2006
Bremner-Harrison S, Harrison SWR, Cypher BL, Murdoch JD, Maldonado J, Darden SK (2006). Development of a single-sampling noninvasive hair snare.
Wildlife Society Bulletin,
34(2), 456-461.
Abstract:
Development of a single-sampling noninvasive hair snare
Noninvasive hair and fecal DNA sampling provides a means of collecting information on elusive species, while causing little or no disturbance. However, current methods of hair collection do not preclude multiple sampling, thus risking sample contamination. We developed a hair snare that prevents multiple sampling, is cost-effective, easy to construct, and safe for target and nontarget species. Our initial field tests on endangered San Joaquin kit foxes (Vulpes macrotis mutica) and swift foxes (Vulpes velox) suggest that this hair snare may be effective in collecting uncontaminated samples for DNA analysis.
Abstract.
Darden SK, Dabelsteen T (2006). Ontogeny of swift fox Vulpes velox vocalizations: Production, usage and response.
Behaviour,
143(6), 659-681.
Abstract:
Ontogeny of swift fox Vulpes velox vocalizations: Production, usage and response
Three processes, production, usage, and response, can be used to describe vocal ontogeny. They may develop independently of each other for a given vocalization and a given species as a result of the different selective pressures associated with each process. We have investigated vocal ontogeny in the swift fox Vulpes velox, using recordings and observations of captive foxes from the time of natal den emergence (age 3-4 weeks) to the time of natal dispersal in the wild (age 4-5 months). We first classified adult vocalizations used during the mating and pup rearing seasons into vocal types (19 types in total) and found that swift foxes have a vocal repertoire comparable in size and diversity to other canids. The repertoire of juvenile foxes contained 16 of the 19 adult-type vocalizations and one juvenile vocalization by age 10 weeks, after which no new types appeared by the end of the study period. Two of the 3 adult vocalizations not observed in juveniles appear to be associated with mating and possibly territoriality and the third is a high intensity alarm vocalization. Apart from 3 vocal types (1 alarm and 2 non-agonistic), once vocalizations had appeared in the juvenile repertoire, they did not seem to change in context over time. Juvenile responses to 5 vocalizations emitted by adults (3 alarm, 1 agonistic, and 1 non-agonistic) appeared to change with increasing age to approach adult-type responses. The emergence of these adult-type responses to 2 of the 3 alarm vocalizations coincided with their first appearance in the juvenile repertoire. The results indicate that there is variation in the degree (in terms of the number of vocal types) of modification over time among the three processes. © Brill Academic Publishers 2006.
Abstract.
2003
Darden SK, Dabelsteen T, Pedersen SB (2003). A potential tool for swift fox (Vulpes velox) conservation: Individuality of long-range barking sequences.
Journal of Mammalogy,
84(4), 1417-1427.
Abstract:
A potential tool for swift fox (Vulpes velox) conservation: Individuality of long-range barking sequences
Vocal individuality has been found in a number canid species. This natural variation can have applications in several aspects of species conservation, from behavioral studies to estimating population density or abundance. The swift fox (Vulpes velox) is a North American canid listed as endangered in Canada and extirpated, endangered, or threatened in parts of the United States. The barking sequence is a long-range vocalization in the species' vocal repertoire. It consists of a series of barks and is most common during the mating season. We analyzed barking sequences recorded in a standardized context from 20 captive individuals (3 females and 17 males) housed in large, single-pair enclosures at a swift fox breeding facility. Using a discriminant function analysis with 7 temporal and spectral variables measured on barking sequences, we were able to correctly classify 99% of sequences to the correct individual. The most important discriminating variable was the mean spacing of barks in a barking sequence. Potential applications of such vocal individuality are discussed.
Abstract.
Darden SK, Pedersen SB, Dabelsteen T (2003). Methods of frequency analysis of a complex mammalian vocalisation.
Bioacoustics,
13(3), 247-263.
Abstract:
Methods of frequency analysis of a complex mammalian vocalisation
The prevalence of complex acoustic structures in mammalian vocalisations can make it difficult to quantify frequency characteristics. We describe two methods developed for the frequency analysis of a complex swift fox Vulpes velox vocalisation, the barking sequence: (1) autocorrelation function analysis and (2) instantaneous frequency analysis. The autocorrelation function analysis results in an energy density spectrum of the signal's averaged amplitude and frequency information. This analysis was used for locating possible formant structures and quantifying the energy distribution of single barks in the barking sequence. The instantaneous frequency analysis is applied to individual continuous frequency bands and generates frequency contours with a resolution of a couple of Hertz. It was used to quantify frequency modulation and calculate average frequencies of harmonic bands in individual barks and to estimate fundamental frequencies. This second method of analysis had to be evaluated with spectrographic analysis to gauge its reliability for each band analysed. The algorithms used should make both of these methods applicable to other complex vocalisations. © 2003 AB Academic Publishers.
Abstract.
Darden S, Dabelsteen T, Pedersen SB (2003). Methods of frequency analysis of a complex mammalian vocalisation. Bioacoustics 13, 247-263. Bioacoustics, 13, 247-263.
