Sasha R. X. Dall

Sexual selection and animal personality

Consistent individual behavioural tendencies, termed “personalities”, have been identified in a wide range of animals. Functional explanations for personality have been proposed, but as yet, very little consideration has been given to a possible role for sexual selection in maintaining differences in personality and its stability within individuals. We provide an overview of the available literature on the role of personality traits in intrasexual competition and mate choice in both human and non‐human animals and integrate this into a framework for considering how sexual selection can generate and maintain personality. For this, we consider the evolution and maintenance of both main aspects of animal personality: inter‐individual variation and intra‐individual consistency.

Sex differences, social context and personality in zebra finches, Taeniopygia guttata

Despite burgeoning interest in consistent individual differences in behaviour (animal ‘personality’), the influence of social interactions on the performance of different behavioural types is poorly understood. Similarly, the ecological and evolutionary consequences of personality differences in social contexts remain unexplored. Moreover, the possibility that the sexes differ in the degree to which they exhibit personality in both social and nonsocial contexts has not yet received serious attention, despite the sexes usually being subject to differing selection pressures. Using a highly gregarious species, the zebra finch, we tested for consistent behavioural differences (in exploration) between individuals of both sexes in both nonsocial and social contexts, the latter considering the behavioural influence of opposite-sex companions. We then investigated how exploratory tendencies relate to behaviour in a potentially risky foraging context in mixed-sex dyads of individuals with differing personalities. Males were not more exploratory on average but were more consistent in their exploratory tendencies than females. Additionally, males behaved more consistently across the social and asocial contexts than females, even though individuals of both sexes similarly influenced each others exploratory behaviour within the social context: the more exploratory the companion, the more exploratory the focal individual (relative to its level of exploration in the asocial context). An individuals exploration also affected its performance in the social foraging context. Our results stress the importance of looking for sex differences in personality and of considering the influence of social context in animal personality studies. We discuss our findings and their implications in the light of the biology of the species and set them in a broader ecological and evolutionary context.

Estimating individual contributions to population growth: evolutionary fitness in ecological time

Ecological and evolutionary change is generated by variation in individual performance. Biologists have consequently long been interested in decomposing change measured at the population level into contributions from individuals, the traits they express and the alleles they carry. We present a novel method of estimating individual contributions to population growth and changes in distributions of quantitative traits and alleles. An individuals contribution to population growth is an individuals realized annual fitness. We demonstrate how the quantities we develop can be used to address a range of empirical questions, and provide an application to a detailed dataset of Soay sheep. The approach provides results that are consistent with those obtained using lifetime estimates of individual performance, yet is substantially more powerful as it allows lifetime performance to be decomposed into annual survival and fecundity contributions.

Evolution of trust and trustworthiness: social awareness favours personality differences

Interest in the evolution and maintenance of personality is burgeoning. Individuals of diverse animal species differ in their aggressiveness, fearfulness, sociability and activity. Strong trade-offs, mutation–selection balance, spatio-temporal fluctuations in selection, frequency dependence and good-genes mate choice are invoked to explain heritable personality variation, yet for continuous behavioural traits, it remains unclear which selective force is likely to maintain distinct polymorphisms. Using a model of trust and cooperation, we show how allowing individuals to monitor each others cooperative tendencies, at a cost, can select for heritable polymorphisms in trustworthiness. This variation, in turn, favours costly ‘social awareness’ in some individuals. Feedback of this sort can explain the individual differences in trust and trustworthiness so often documented by economists in experimental public goods games across a range of cultures. Our work adds to growing evidence that evolutionary game theorists can no longer afford to ignore the importance of real world inter-individual variation in their models.

Pairs of zebra finches with similar 'personalities' make better parents

Although behavioural plasticity should be an advantage in a varying world, there is increasing evidence for widespread stable individual differences in the behaviour of animals: that is, ‘personality’. Here we provide evidence suggesting that sexual selection is an important factor in the evolution of personality in species with biparental care. We carried out a cross-fostering breeding experiment on zebra finches, Taeniopygia guttata, and found that parental personality traits and the combination of personalities within breeding pairs had positive effects on correlates of (foster) offspring fitness (body mass and condition). Furthermore, these nongenetic parental effects were pervasive and carried over into the next generation. Our results suggest that similarity in behavioural traits of biparental species can have important, long-lasting effects on reproductive success, probably because of reduced sexual conflict over the provision of parental investment.

Predictive systems ecology

Human societies, and their well-being, depend to a significant extent on the state of the ecosystems that surround them. These ecosystems are changing rapidly usually in response to anthropogenic changes in the environment. To determine the likely impact of environmental change on ecosystems and the best ways to manage them, it would be desirable to be able to predict their future states. We present a proposal to develop the paradigm of predictive systems ecology, explicitly to understand and predict the properties and behaviour of ecological systems. We discuss the necessary and desirable features of predictive systems ecology models. There are places where predictive systems ecology is already being practised and we summarize a range of terrestrial and marine examples. Significant challenges remain but we suggest that ecology would benefit both as a scientific discipline and increase its impact in society if it were to embrace the need to become more predictive.

Badger social networks correlate with tuberculosis infection

Although disease hosts are classically assumed to interact randomly [1], infection is likely to spread across structured and dynamic contact networks [2]. We used social network analyses to investigate contact patterns of group-living European badgers, Meles meles, which are an important wildlife reservoir of bovine tuberculosis (TB). We found that TB test-positive badgers were socially isolated from their own groups but were more important for flow, potentially of infection, between social groups. The distinctive social position of infected badgers may help explain how social stability mitigates, and social perturbation increases, the spread of infection in badgers.

Personality variation in a clonal insect: The pea aphid, Acyrthosiphon pisum

Individuals are often consistent in their behavior but vary from each other in the level of behavior shown. Despite burgeoning interest in such animal personality variation, studies on invertebrates are scarce, and studies on clonal invertebrates nonexistent. This is surprising given the obvious advantages of using invertebrates/clones to tackle the crucial question why such consistent behavioral differences exist. Here we show that individuals of clonal pea aphids exhibit consistent behavioral differences in their escape responses to a predator attack (dropping vs. nondropping off a plant). However, behavior was not repeatable at the clonal level. Genetically identical clones expressed various phenotypes but different clones produced different proportions of each phenotype (dropper, nondropper, and inconsistent). Manipulations of early environmental conditions had little qualitative impact on such patterns. We discuss the importance of our findings for future studies of the evolutionary and ecological consequences of personality variation.

An empiricist guide to animal personality variation in ecology and evolution

The study of animal personality variation promises to provide significant new insight into the way that behaviour evolves in animals, along with its ecological and evolutionary influences. We strongly advocate more empirical work in this exciting and rapidly expanding research area, but hope that new studies adopt a more hypothesis-driven and/or experimental approach than seems to be usual at the moment. Here we outline what we feel is “good practice” to the many empiricists that are keen on pursuing work in this field. We highlight the substantial body of theoretical work that exists for providing well-reasoned hypotheses, which new empirical studies should be designed to test. Furthermore, using a brief review of existing work on the behavioural ecology of animal personality variation in the zebra finch - one of the more widely used model systems in this field - we stress the importance of understanding the ecology of the chosen study animal, and the problems that are likely to arise by neglecting to identify or account for the structure of behavioural variation that is often likely to occur.

Are behavioral syndromes invariant? Spatiotemporal variation in shy/bold behavior in squid

Behavioral syndromes are correlated suites of behavior, analogous to human personality traits. Most work to date has been taken from limited “snapshots” in space and time, with the implicit assumption that a behavioral syndrome is an invariant property, fixed by evolutionary constraints or adaptations. However, directional selection on two mechanistically independent traits (selective covariance) could also result in correlated behaviors. Previously, we have shown that shy/bold behavior in Southern dumpling squid (Euprymna tasmanica) across predator encounter and feeding risk contexts is genetically and phenotypically uncoupled, and hence potentially free to vary independently. Here, we collected data on shy/bold behaviors from two independent wild populations of squid in two different years to test whether behavioral correlations across these same two functional contexts vary through time and space. We detected significant influences of population, sex, and body size on the expression of boldness in squid within each functional context, and this was coupled with significant differences in relative population density and adult sex ratio. Despite these changes in behavior and demographic parameters, we found that correlations between boldness scores across the two functional contexts were largely absent in both wild populations of squid in both years. Our work suggests that some animal groups may be largely characterized by context-specific behavioral expression. A theoretical framework which conceptualizes behavioral syndromes resulting from context-specific behavioral rules may be needed to fully understand why behaviors are sometimes correlated, and why sometimes they are not.