Animal personalities: consequences for ecology and evolution

Personality and morphological traits affect pigeon survival from raptor attacks

Personality traits have recently been shown to impact fitness in different animal species, potentially making them similarly relevant drivers as morphological and life history traits along the evolutionary pathways of organisms. Predation is a major force of natural selection through its deterministic effects on individual survival, but how predation pressure has helped to shape personality trait selection, especially in free-ranging animals, remains poorly understood. We used high-precision GPS tracking to follow whole flocks of homing pigeons (Columba livia) with known personalities and morphology during homing flights where they were severely predated by raptors. This allowed us to determine how the personality and morphology traits of pigeons may affect their risk of being predated by raptors. Our survival model showed that individual pigeons, which were more tolerant to human approach, slower to escape from a confined environment, more resistant to human handling, with larger tarsi, and with lighter plumage, were more likely to be predated by raptors. We provide rare empirical evidence that the personality of prey influences their risk of being predated under free-ranging circumstances.

Causes and consequences of repeatability, flexibility and individual fine-tuning of migratory timing in pike

Many organisms undertake migrations between foraging and breeding habitats and while it is assumed that reproductive timing affects fitness, little is known about the degree of individual consistency, and about the causes and consequences of individual variation in migratory timing in organisms other than birds. Here, we report on a 6-year mark-recapture study, including 2048 individuals, of breeding migration in anadromous pike (Esox lucius), an iteroparous top-predatory fish that displays homing behaviour. By repeated sampling across years at a breeding site, we first quantify individual variation both within and between breeding events and then investigate phenotypic correlates and fitness consequences of arrival timing to the breeding site. Our data demonstrate that males arrive before females, that large males arrive later than small males, that the timing of breeding migration varies among years and that individuals are consistent in their timing across years relative to other individuals in the population. Furthermore, data on return rates indicate that arrival time is under stabilizing viability selection, and that individuals who are more flexible in their timing of arrival during the first reproductive years survive longer compared with less flexible individuals. Finally, longitudinal data demonstrate that individuals consistently fine-tune their arrival timing across years, showing that the timing of arrival to breeding sites is influenced by experience. These findings represent rare evidence of how between- and within-individual variations in migratory timing across breeding events are correlated with phenotypic and fitness traits in an ecologically important keystone species. Our results emphasize the importance of considering variation in migratory timing both between and within individuals in studies investigating the fitness consequences of migratory behaviour and have implications for future management.

A practical guide and power analysis for GLMMs: detecting among treatment variation in random effects

In ecology and evolution generalized linear mixed models (GLMMs) are becoming increasingly used to test for differences in variation by treatment at multiple hierarchical levels. Yet, the specific sampling schemes that optimize the power of an experiment to detect differences in random effects by treatment/group remain unknown. In this paper we develop a blueprint for conducting power analyses for GLMMs focusing on detecting differences in variance by treatment. We present parameterization and power analyses for random-intercepts and random-slopes GLMMs because of their generality as focal parameters for most applications and because of their immediate applicability to emerging questions in the field of behavioral ecology. We focus on the extreme case of hierarchically structured binomial data, though the framework presented here generalizes easily to any error distribution model. First, we determine the optimal ratio of individuals to repeated measures within individuals that maximizes power to detect differences by treatment in among-individual variation in intercept, among-individual variation in slope, and within-individual variation in intercept. Second, we explore how power to detect differences in target variance parameters is affected by total variation. Our results indicate heterogeneity in power across ratios of individuals to repeated measures with an optimal ratio determined by both the target variance parameter and total sample size. Additionally, power to detect each variance parameter was low overall (in most cases >1,000 total observations per treatment needed to achieve 80% power) and decreased with increasing variance in non-target random effects. With growing interest in variance as the parameter of inquiry, these power analyses provide a crucial component for designing experiments focused on detecting differences in variance. We hope to inspire novel experimental designs in ecology and evolution investigating the causes and implications of individual-level phenotypic variance, such as the adaptive significance of within-individual variation.

Habitat complexity, environmental change and personality: A tropical perspective

Tropical rainforests are species-rich, complex ecosystems. They are increasingly being negatively affected by anthropogenic activity, which is rapidly and unpredictably altering their structure and complexity. These changes in habitat state may expose tropical animals to novel and unpredictable conditions, potentially increasing their extinction risk. However, an animal's ability to cope with environmental change may be linked to its personality. While numerous studies have investigated environmental influences on animal personalities, few are focused on tropical species. In this review, we consider how behavioural syndromes in tropical species might facilitate coping under, and adapting to, increasing disturbance. Given the complexity of tropical rainforests, we first discuss how habitat complexity influences personality traits and physiological stress in general. We then explore the ecological and evolutionary implications of personality in the tropics in the context of behavioural flexibility, range expansion and speciation. Finally, we discuss the impact that anthropogenic environmental change may have on the ecological integrity of tropical rainforests, positing scenarios for species persistence. Maintaining tropical rainforest complexity is crucial for driving behavioural flexibility and personality type, both of which are likely to be key factors facilitating long term persistence in disturbed habitats.

Key Questions on the Role of Phenotypic Plasticity in Eco-Evolutionary Dynamics

Ecology and evolution have long been recognized as reciprocally influencing each other, with recent research emphasizing how such interactions can occur even on very short (contemporary) time scales. Given that these interactions are mediated by organismal phenotypes, they can be variously shaped by genetic variation, phenotypic plasticity, or both. I here address 8 key questions relevant to the role of plasticity in eco-evolutionary dynamics. Focusing on empirical evidence, especially from natural populations, I offer the following conclusions. 1) Plasticity is--not surprisingly--sometimes adaptive, sometimes maladaptive, and sometimes neutral. 2) Plasticity has costs and limits but these constraints are highly variable, often weak, and hard to detect. 3) Variable environments favor the evolution of increased trait plasticity, which can then buffer fitness/performance (i.e., tolerance). 4) Plasticity sometimes aids colonization of new environments (Baldwin Effect) and responses to in situ environmental change. However, plastic responses are not always necessary or sufficient in these contexts. 5) Plasticity will sometimes promote and sometimes constrain genetic evolution. 6) Plasticity will sometimes help and sometimes hinder ecological speciation but, at present, empirical tests are limited. 7) Plasticity can show considerable evolutionary change in contemporary time, although the rates of this reaction norm evolution are highly variable among taxa and traits. 8) Plasticity appears to have considerable influences on ecological dynamics at the community and ecosystem levels, although many more studies are needed. In summary, plasticity needs to be an integral part of any conceptual framework and empirical investigation of eco-evolutionary dynamics.

Spatial ecology of coastal Atlantic cod Gadus morhua associated with parasite load

Acoustic tags and receivers were used to investigate the spatial ecology of coastal Atlantic cod Gadus morhua (n = 32, mean fork length: 50 cm, range: 33-80 cm) on the Norwegian Skagerrak coast in 2012. Monthly home ranges (HR), swimming activity and depth use varied considerably among individuals and through the months of June, July and August. HR sizes for the period ranged from 0.25 to 5.20 km2 (mean = 2.30 km2. Two thirds of the tagged G. morhua were infected with black spot disease Cryptocotyle lingua parasites; these fish had larger HRs and occupied deeper water compared with non-infected fish. The infected fish also tended to be more active in terms of horizontal swimming. From an ecological and evolutionary perspective, any environmental change that modifies G. morhua behaviour may therefore also alter the parasite load of the population, and its conservation and fishery status.

Behavioral syndrome in a native and an invasive hymenoptera species

Recent studies have focused on the role of behavior in biological invasions. Individuals may differ consistently in time for several behavioral traits (personality) which covary (behavioral syndrome) resulting in different behavioral types, some of them favoring invasion. Social hymenopterans have a strong potential to be invaders and their success depends primarily on the foundresses' ability to found viable colonies. They are expected to be active, explorative and bold for optimally establishing their nest. In Europe, 2 hornet species coexist: the native Vespa crabro and the invasive Vespa velutina. These 2 species may compete for nesting sites and we suggest that the initial success of V. velutina has been favored by its behavior in outperforming V. crabro for the traits involved in nest initiation. Here, we (i) defined the personality of V. crabro and V. velutina, (ii) tested for the existence of behavioral syndrome in these species, and (iii) compared their performances using an open-field test. Our results show that V. crabro foundresses behave consistently but not V. velutina; this lack of consistency being mainly due to reduced variance among individuals. This result questions the possibility of detecting consistent behavioral differences in species having recently undergone a strong bottleneck. Both species exhibit the same correlations between activity, boldness and exploration and V. velutina clearly outperforms V. crabro for all traits. Our results suggest that activity, boldness, and exploration are implicated in both hornet nest initiation and invasion process which contributed to explain why social hymenopterans are so successful at colonization.

Emergence of Leadership within a Homogeneous Group

Large scale coordination without dominant, consistent leadership is frequent in nature. How individuals emerge from within the group as leaders, however transitory this position may be, has become an increasingly common question asked. This question is further complicated by the fact that in many of these aggregations, differences between individuals are minor and the group is largely considered to be homogeneous. In the simulations presented here, we investigate the emergence of leadership in the extreme situation in which all individuals are initially identical. Using a mathematical model developed using observations of natural systems, we show that the addition of a simple concept of leadership tendencies which is inspired by observations of natural systems and is affected by experience can produce distinct leaders and followers using a nonlinear feedback loop. Most importantly, our results show that small differences in experience can promote the rapid emergence of stable roles for leaders and followers. Our findings have implications for our understanding of adaptive behaviors in initially homogeneous groups, the role experience can play in shaping leadership tendencies, and the use of self-assessment in adapting behavior and, ultimately, self-role-assignment.

Behaviour in captivity predicts some aspects of natural behaviour, but not others, in a wild cricket population

Examining the relevance of 'animal personality' involves linking consistent among- and within-individual behavioural variation to fitness in the wild. Studies aiming to do this typically assay personality in captivity and rely on the assumption that measures of traits in the laboratory reflect their expression in nature. We examined this rarely tested assumption by comparing laboratory and field measurements of the behaviour of wild field crickets (Gryllus campestris) by continuously monitoring individual behaviour in nature, and repeatedly capturing the same individuals and measuring their behaviour in captivity. We focused on three traits that are frequently examined in personality studies: shyness, activity and exploration. All of them showed repeatability in the laboratory. Laboratory activity and exploration predicted the expression of their equivalent behaviours in the wild, but shyness did not. Traits in the wild were predictably influenced by environmental factors such as temperature and sunlight, but only activity showed appreciable within-individual repeatability. This suggests that some behaviours typically studied as personality traits can be accurately assayed in captivity, but the expression of others may be highly context-specific. Our results highlight the importance of validating the relevance of laboratory behavioural assays to analogous traits measured in the wild.

Effect of hunger level and time of day on boldness and aggression in the zebrafish Danio rerio

The effect of two environmental variables, hunger level (fed or not fed before behavioural assays) and time of day (morning or afternoon), on the boldness and aggressiveness of male and female zebrafish Danio rerio, was tested. The results showed that neither hunger level nor time of testing influenced boldness in males and females, but hunger level significantly affected aggression in females when compared with males.

Spying on small wildlife sounds using affordable collar-mounted miniature microphones: an innovative method to record individual daylong vocalisations in chipmunks

Technological advances can greatly benefit the scientific community by making new areas of research accessible. The study of animal vocal communication, in particular, can gain new insights and knowledge from technological improvements in recording equipment. Our comprehension of the acoustic signals emitted by animals would be greatly improved if we could continuously track the daily natural emissions of individuals in the wild, especially in the context of integrating individual variation into evolutionary ecology research questions. We show here how this can be accomplished using an operational tiny audio recorder that can easily be fitted as an on-board acoustic data-logger on small free-ranging animals. The high-quality 24 h acoustic recording logged on the spy microphone device allowed us to very efficiently collect daylong chipmunk vocalisations, giving us much more detailed data than the classical use of a directional microphone over an entire field season. The recordings also allowed us to monitor individual activity patterns and record incredibly long resting heart rates, and to identify self-scratching events and even whining from pre-emerging pups in their maternal burrow.

Examining the role of testosterone in mediating short-term aggressive responses to social stimuli in a lizard

Hormones have been suggested as a key proximate mechanism that organize and maintain consistent individual differences in behavioural traits such as aggression. The steroid hormone testosterone in particular has an important activational role in mediating short-term aggressive responses to social and environmental stimuli within many vertebrate systems. We conducted two complementary experiments designed to investigate the activational relationship between testosterone and aggression in male Egernia whitii, a social lizard species. First, we investigated whether a conspecific aggressive challenge induced a testosterone response and second, we artificially manipulated testosterone concentrations to examine whether this changed aggression levels. We found that at the mean level, plasma T concentration did not appear to be influenced by an aggression challenge. However, there was a slight indication that receiving a challenge may influence intra-individual consistency of plasma T concentrations, with individuals not receiving an aggression challenge maintaining consistency in their circulating testosterone concentrations, while those individuals that received a challenge did not. Manipulating circulating testosterone concentrations had no influence on either mean-level or individual-level aggression. Combined with our previous work, our study adds increasing evidence that the relationship between testosterone and aggression is not straightforward, and promotes the investigation of alternative hormonal pathways and differences in neuro-synthesis and neuroendocrine pathways to account for species variable testosterone - aggression links.

Effects of emergence time and early social rearing environment on behaviour of Atlantic salmon: consequences for juvenile fitness and smolt migration

Consistent individual differences in behaviour have been well documented in a variety of animal taxa, but surprisingly little is known about the fitness and life-history consequences of such individual variation. In wild salmonids, the timing of fry emergence from gravel spawning nests has been suggested to be coupled with individual behavioural traits. Here, we further investigate the link between timing of spawning nest emergence and behaviour of Atlantic salmon (Salmo salar), test effects of social rearing environment on behavioural traits in fish with different emergence times, and assess whether behavioural traits measured in the laboratory predict growth, survival, and migration status in the wild. Atlantic salmon fry were sorted with respect to emergence time from artificial spawning nest into three groups: early, intermediate, and late. These emergence groups were hatchery-reared separately or in co-culture for four months to test effects of social rearing environment on behavioural traits. Twenty fish from each of the six treatment groups were then subjected to three individual-based behavioural tests: basal locomotor activity, boldness, and escape response. Following behavioural characterization, the fish were released into a near-natural experimental stream. Results showed differences in escape behaviour between emergence groups in a net restraining test, but the social rearing environment did not affect individual behavioural expression. Emergence time and social environment had no significant effects on survival, growth, and migration status in the stream, although migration propensity was 1.4 to 1.9 times higher for early emerging individuals that were reared separately. In addition, despite individuals showing considerable variation in behaviour across treatment groups, this was not translated into differences in growth, survival, and migration status. Hence, our study adds to the view that fitness (i.e., growth and survival) and life-history predictions from laboratory measures of behaviour should be made with caution and ideally tested in nature.

Focus on the success of others leads to selfish behavior

It has often been argued that the spectacular cognitive capacities of humans are the result of selection for the ability to gather, process, and use information about other people. Recent studies show that humans strongly and consistently differ in what type of social information they are interested in. Although some individuals mainly attend to what the majority is doing (frequency-based learning), others focus on the success that their peers achieve with their behavior (success-based learning). Here, we show that such differences in social learning have important consequences for the outcome of social interactions. We report on a decision-making experiment in which individuals were first classified as frequency- and success-based learners and subsequently grouped according to their learning strategy. When confronted with a social dilemma situation, groups of frequency-based learners cooperated considerably more than groups of success-based learners. A detailed analysis of the decision-making process reveals that these differences in cooperation are a direct result of the differences in information use. Our results show that individual differences in social learning strategies are crucial for understanding social behavior.

Genetic influences on response to novel objects and dimensions of personality in Papio baboons

Behavioral variation within and between populations and species of the genus Papio has been studied extensively, but little is known about the genetic causes of individual- or population-level differences. This study investigates the influence of genetic variation on personality (sometimes referred to as temperament) in baboons and identifies a candidate gene partially responsible for the variation in that phenotype. To accomplish these goals, we examined individual variation in response to both novel objects and an apparent novel social partner (using a mirror test) among pedigreed baboons (n = 578) from the Southwest National Primate Research Center. We investigated the frequency and duration of individual behaviors in response to novel objects and used multivariate factor analysis to identify trait-like dimensions of personality. Exploratory factor analysis identified two distinct dimensions of personality within this population. Factor 1 accounts for 46.8 % of the variance within the behavioral matrix, and consists primarily of behaviors related to the "boldness" of the subject. Factor 2 accounts for 18.8 % of the variation, and contains several "anxiety" like behaviors. Several specific behaviors, and the two personality factors, were significantly heritable, with the factors showing higher heritability than most individual behaviors. Subsequent analyses show that the behavioral reactions observed in the test protocol are associated with animals' social behavior observed later in their home social groups. Finally we used linkage analysis to map quantitative trait loci for the measured phenotypes. Single nucleotide polymorphisms in a positional candidate gene (SNAP25) are associated with variation in one of the personality factors, and CSF levels of homovanillic acid and 3-methoxy-4-hydroxyphenylglycol. This study documents heritable variation in personality among baboons and suggests that sequence variation in SNAP25 may influence differences in behavior and neurochemistry in these nonhuman primates.

Repeatability in the contact calling system of Spix's disc-winged bat (Thyroptera tricolor)

Spix's disc-winged bat (Thyroptera tricolor) forms cohesive groups despite using an extremely ephemeral roost, partly due to the use of two acoustic signals that help individuals locate roost sites and group members. While the calls that aid in group cohesion are commonly used, some bats rarely or never produce them. Here, we examine whether the differences observed in the contact calling behaviour of T. tricolor are repeatable; that is, whether individual differences are consistent. We recorded contact calls of individuals in the field and rates and patterns of vocalization. To determine whether measured variables were consistent within individuals, we estimated repeatability (R), which compares within-individual to among-individual variance in behavioural traits. Our results show that repeatability for call variables was moderate but significant, and that repeatability was highest for the average number of calls produced (R=0.46-0.49). Our results demonstrate important individual differences in the contact calling behaviour of T. tricolor; we discuss how these could be the result of mechanisms such as frequency-dependent selection that favour groups composed of individuals with diverse vocal strategies. Future work should address whether changes in social environment, specifically group membership and social status, affect vocal behaviour.

Animal personality and state-behaviour feedbacks: a review and guide for empiricists

An exciting area in behavioural ecology focuses on understanding why animals exhibit consistent among-individual differences in behaviour (animal personalities). Animal personality has been proposed to emerge as an adaptation to individual differences in state variables, leading to the question of why individuals differ consistently in state. Recent theory emphasizes the role that positive feedbacks between state and behaviour can play in producing consistent among-individual covariance between state and behaviour, hence state-dependent personality. We review the role of feedbacks in recent models of adaptive personalities, and provide guidelines for empirical testing of model assumptions and predictions. We discuss the importance of the mediating effects of ecology on these feedbacks, and provide a roadmap for including state-behaviour feedbacks in behavioural ecology research.

Corticosterone stress response shows long-term repeatability and links to personality in free-living Nazca boobies

The concept of "coping styles", or consistently different responses to stressors, is of broad interest in behavioral ecology and biomedicine. Two critical predictions of this concept are individual consistency of neurophysiological and behavioral responses (relative to population variability) and a negative relationship between aggression/proactivity and hypothalamic-pituitary-adrenal axis reactivity. Recent studies failed to provide strong support for these predictions, especially outside of strictly controlled conditions, and long-term measures to test the first prediction are rare. Here, we demonstrate individual repeatability across 2-3years of maximum circulating corticosterone concentration [CORT] and area under the [CORT] response curve (AUCI) during a standard capture-restraint test in wild, free-living adult Nazca boobies (Sula granti). We also show that the stress response predicts the personality traits aggression and anxiety in these birds (measured in the wild); however, the strength of these results was weak. Maximum [CORT] and AUCI showed higher repeatability between years than baseline [CORT]. After controlling breeding status, sex, mass, date sampled, and their interactions, baseline [CORT] was most closely related to personality traits, followed by AUCI, and then maximum [CORT]. The direction of these relationships depended on whether the testing context was social or non-social. [CORT] parameters had little to no relationship with cross-context plasticity in personality traits. Our results generally affirm two critical predictions of coping styles, but match the emerging trend that these relationships are weak in the wild, and may depend on testing context.

Baseline and stress-induced glucocorticoid concentrations are not repeatable but covary within individual great tits (Parus major)

In evolutionary endocrinology, there is a growing interest in the extent and basis of individual variation in endocrine traits, especially circulating concentrations of hormones. This is important because if targeted by selection, such individual differences present the opportunity for an evolutionary response to selection. It is therefore necessary to examine whether hormone traits are repeatable in natural populations. However, research in this area is complicated by the fact that different hormone traits can be correlated. The nature of these trait correlations (i.e., phenotypic, within-, or among-individual) is critically relevant in terms of the evolutionary implications, and these in turn, depend on the repeatability of each hormone trait. By decomposing phenotypic correlations between hormone traits into their within- and among-individual components it is possible to describe the multivariate nature of endocrine traits and generate inferences about their evolution. In the present study, we repeatedly captured individual great tits (Parus major) from a wild population and measured plasma concentrations of corticosterone. Using a mixed-modeling approach, we estimated repeatabilities in both initial (cf. baseline; CORT0) and stress-induced concentrations (CORT30) and the correlations between those traits among- and within-individuals. We found a lack of repeatability in both CORT0 and CORT30. Moreover, we found a strong phenotypic correlation between CORT0 and CORT30, and due to the lack of repeatability for both traits, there was no among-individual correlation between these two traits-i.e., an individual's average concentration of CORT0 was not correlated with its average concentration of CORT30. Instead, the phenotypic correlation was the result of a strong within-individual correlation, which implies that an underlying environmental factor co-modulates changes in initial and stress-induced concentrations within the same individual over time. These results demonstrate that (i) a phenotypic correlation between two hormone traits does not imply that the traits are correlated among individuals; (ii) the importance of repeated sampling to partition within- and among-individual variances and correlations among labile physiological traits; and (iii) that environmental factors explain a considerable fraction of the variation and co-variation in hormone concentrations.