Consistent Between-individual Differences Research Articles

The association between personalities, alternative breeding strategies and reproductive success in dunnocks.

Although consistent between-individual differences in behaviour (i.e. animal personality) are ubiquitous in natural populations, relatively few studies have examined how personalities influence the formation of social relationships. Yet, behavioural characteristics of both sexes might be key when it comes to pair-bond formation, and cooperation with partners to successfully rear offspring. We here use a wild population of dunnocks (Prunella modularis) to first investigate whether individuals mate nonrandomly (i.e. assortative mating) with regard to four behavioural traits-flight-initiation distance (FID), provisioning, activity and vigilance-that differ in repeatability and have previously been associated with mating patterns and fitness in other species. Second, we test whether an individual's FID is associated with variability in the dunnocks' mating system (i.e. monogamous pairs vs. polygamous groups). Finally, we determine whether FID and provisioning of males and females associate with their reproductive success. We found no statistical support for assortative mating in FID between males and females. Interestingly, in polygamous groups, co-breeding males differed in their FIDs with dominant alpha males having significantly shorter FIDs compared with subordinate beta-males. Moreover, there was evidence for assortative mating in provisioning for alpha males and females in polygamous groups. We also found that male provisioning influenced reproductive success of both sexes, whereas female provisioning rates only positively correlated with her own but not their partner(s) reproductive output. Our results suggest that personality differences may have important implications for social relationships, the emergence of different mating patterns and ultimately reproductive success within populations.

Evidence for animal personalities in two Brazilian tortoises (Chelonoidis denticulatus and Chelonoidis carbonarius) and insights for their conservation

Animal personality, the consistent between-individual differences in e.g., risk-taking, exploration, antipredator or mating behaviours, has major impacts on the fitness of individuals in many species. Understanding how to quantify animal personality should help us predicting how species interact with their environment and with the current environmental changes. We adapted existing behavioural assays to quantify the personality of two Brazilian tortoises, Chelonoidis carbonarius and C. denticulatus. We recorded behavioural responses to stress, novel environments, novel objects and social encounters. Behavioural components were consistent through time, supporting the existence of personality in both species. These behaviours were further correlated and could be summarized into two behavioural axes with recognizable biological meanings. One axis was related to responses to threats and novelty, as well as interest and interaction behaviours towards conspecifics and one to submission. The behavioural dimensions were similar in both species, suggesting that they share the same behavioural syndromes, but C. carbonarius had greater frequency of risk taking behaviours. This pattern can be related to differences in resource availabilities and predator pressures in their respective natural habitats. Within each species, however, the individual variation in morphology only had a weak effect on personality and males tended to show more signs of submission. Further studies are needed to investigate the role of habitat features (resource availabilities and predation risk) on individual behavioural variation in each species in order to improve conservation and translocations programs.

Ain\u2019t going down without a fight: state-and environment-dependence of antipredator defensive aggressive personalities in Carpetan rock lizard

Aggression is one of the most frequently studied behavioural traits across a wide range of taxa; however, most studies evaluate aggressive behaviour in a social context, in which aggressive interactions between conspecifics are motivated by resource control (offensive or social aggression). However, in an antipredator context, the primary role of aggression is defence (defensive or antipredator aggression). Although the neuroendocrinology of antipredator aggression is often studied in domesticated and laboratory animals, how environment and individual state affect this behavioural trait in the wild is largely unknown. Here, by conducting a manipulative experiment, we tested whether (i) consistent between-individual differences (i.e. animal personality) are present in antipredator aggression in adult male Carpetan rock lizards (Iberolacerta cyreni) and (ii) short-term environmental changes (presence vs. absence of predator cues) and differences in individual state (body length, head size, hind limb length) affect individual mean behaviour (i.e. behavioural type). We found moderate-high repeatability in antipredator aggression (willingness to bite a human), indicating the presence of animal personality in this behavioural trait. Lizards were on average more defensive in the presence of predator cues; furthermore, short-legged males showed higher antipredator aggression than long-legged males in the presence of predator cues, probably as an attempt to balance their decreased escape speed. Larger (~ older) males were more defensive than smaller ones, probably due to their increased fighting ability. We conclude that antipredator aggression is an important part of an individual’s behavioural repertoire and its expression is driven by both environmental situation and individual state.Significance statementAntipredator/defensive aggression is not the primary antipredatory response; however, when other ways of escape are not possible, actually hurting the predator could be the only way of survival. While this behaviour obviously has substantial effects on fitness, it is severely understudied compared to social/offensive aggression. In a manipulative experiment, we found that there are consistent between-individual differences in antipredator aggression (i.e. willingness to bite during handling) of adult male Carpetan rock lizards (Iberolacerta cyreni), supporting the presence of animal personality and suggesting that this behavioural trait might respond to natural selection. Furthermore, short-term environmental variation (i.e. presence vs. absence of predator cues) in interaction with individual state affected antipredator aggression of individuals, emphasising the ecological and evolutionary relevance of this behaviour.

Female spider aggression is associated with genetic underpinnings of the nervous system and immune response to pathogens.

Identifying the genetic architecture underlying phenotypic variation in natural populations and assessing the consequences of polymorphisms for individual fitness are fundamental goals in evolutionary and molecular ecology. Consistent between-individual differences in behaviour have been documented for a variety of taxa. Dissecting the genetic basis of such behavioural differences is however a challenging endeavour. The molecular underpinnings of natural variation in aggression remain elusive. Here, we used comparative gene expression (transcriptome analysis and RT-PCR), genetic association analysis and pharmacological experiments to gain insight into the genetic basis of aggression in wild-caught jumping spiders (Portia labiata). We show that spider aggression is associated with a putative viral infection response gene, BTB/POZ domain-containing protein 17 (BTBDH), in addition to a putative serotonin receptor 1A (5-HT1A) gene. Spider aggression varies with virus loads, and BTBDH is upregulated in docile spiders and exhibits a genetic variant associated with aggression. We also identify a putative serotonin receptor 5-HT1A gene upregulated in docile P. labiata. Individuals that have been treated with serotonin become less aggressive, but individuals treated with a nonselective serotonin receptor antagonist (methiothepin) also reduce aggression. Further, we identify the genetic variants in the 5-HT1A gene that are associated with individual variation in aggression. We therefore conclude that co-evolution of the immune and nervous systems may have shaped the between-individual variation in aggression in natural populations of jumping spiders.

Zebra finches bi-directionally selected for personality differ in repeatability of corticosterone and testosterone

Consistent between-individual differences in behaviour have been documented across the animal kingdom. Such variation between individuals has been shown to be the basis for selection and to act as a pacemaker for evolutionary change. Recently, equivocal evidence suggests that such consistent between-individual variation is also present in hormones. This observation has sparked interest in understanding the mechanisms shaping individual differences, temporal consistency and heritability of hormonal phenotypes and to understand, if and to what extent hormonal mechanisms are involved in mediating consistent variation in behaviour between individuals. Here, we used zebra finches of the fourth generation of bi-directionally selected lines for three independent behaviours: aggression, exploration and fearlessness. We investigated how these behaviours responded to artificial selection and tested their repeatability. We further tested for repeatability of corticosterone and testosterone across and within lines. Moreover, we are presenting the decomposed variance components for within-individual variance (i.e. flexibility) and between-individual variance (i.e. more or less pronounced differences between individuals) and investigate their contribution to repeatability estimates. Both hormones as well as the exploration and fearlessness but not aggressiveness, were repeatable. However, variance components and hence repeatability differed between lines and were often lower than in unselected control animals, mainly because of a reduction in between-individual variance. Our data show that artificial selection (including active selection and genetic drift) can affect the mean and variance of traits. We stress the importance for understanding how variable a trait is both between and within individuals to assess the selective value of a trait.

Do female rainbow kribs choose males on the basis of their apparent aggression and boldness? A non-correlational mate choice study

Consistent between-individual differences in behaviour, known as personality differences, are heritable and have consequences for individual survival and reproductive success. Therefore, it is likely that personality differences are not just under natural but also under sexual selection. Indeed, the recently developed idea that individuals choose their mate based on its personality finds empirical support. However, most studies on mate choice based on personality traits are correlative pioneering work and there is a paucity of experimental studies that test for causality by disentangling personality measures from other, potentially correlated traits that may be important during mate choice. Here, we tested female preference for the apparent level and consistency of either male aggression (measured as mean distance of approach towards an animated opponent, manipulated by locating males at a fixed distance) or male boldness (measured as activity under a simulated predation threat, manipulated using a gradient in ambient water temperature) in a bi-parental West African cichlid, Pelvicachromis pulcher. Females could observe the apparent behaviour of paired stimulus males and were allowed to choose between the two stimulus males in a subsequent choice test. We found no direct effect of male apparent aggression/boldness on female choice, but an indirect effect such that female preference for the apparently bold male increased with increasing within-male pair contrast in their apparent level of boldness. Our results indicate females consider male boldness per se during mate choice, suggesting male boldness is sexually selected in our study species.Significance statementEver since Darwin introduced the concept of sexual selection, female choice has been studied extensively. However, the hypothesis that consistent between-individual differences in behaviour (known as personality differences) affect mate choice is relatively new. Correlative studies support this idea but provide only suggestive evidence. Here, we used behavioural manipulations in order to disentangle male behaviour from other, potentially correlated male traits, allowing us to test for causality between female choice and personality differences in male aggression and boldness (both in level and consistency of behaviour) in a bi-parental cichlid. We found no overall female preference for male apparent behaviour, but female preference for the bold-appearing male increased with increasing between-male contrast in apparent boldness. Our results indicate a causal link between female choice and male boldness. In future, behavioural manipulations using a temperature gradient could provide further valuable insights.

Males have more aggressive and less sociable personalities than females in semi-captive Asian elephants

Personality, i.e. consistent between-individual differences in behaviour, has been documented in many species. Yet little is known about how males and females of long-lived, highly social species differ in their measures of personality structure. We investigated sex differences in the mean, variance, and covariance of three previously reported personality traits (Attentiveness, Sociability, Aggressiveness) in 150 female and 107 male Asian elephants (Elephas maximus) from a semi-captive population in Myanmar. These three personality traits were obtained by performing exploratory factor analysis on 28 behavioural items that had been rated by experienced elephant handlers. We found that males scored significantly higher on Aggressiveness and tended to score lower on Sociability than females. However, no sex difference was found in the mean scores of Attentiveness. Variances for the three personality traits did not differ between the sexes, suggesting that male and female elephants share the same range of personality variation. Likewise, trait covariances were similar between the sexes. While both sexes show complex sociality in the wild, female Asian elephants typically live in highly social family units, whereas male elephants’ social bonds are weaker. Males usually form dominance ranks by aggressive interactions, especially during musth. Our results on a large sample of individuals living in their natural environment are thus in agreement with elephant life-histories and parallel the findings of sex differences in other long-lived highly social species with similar life-histories.

Brain size predicts behavioural plasticity in guppies (Poecilia reticulata): An experiment.

Understanding how animal personality (consistent between-individual behavioural differences) arises has become a central topic in behavioural sciences. This endeavour is complicated by the fact that not only the mean behaviour of individuals (behavioural type) but also the strength of their reaction to environmental change (behavioural plasticity) varies consistently. Personality and cognitive abilities are linked, and we suggest that behavioural plasticity could also be explained by differences in brain size (a proxy for cognitive abilities), since accurate decisions are likely essential to make behavioural plasticity beneficial. We test this idea in guppies (Poecilia reticulata), artificially selected for large and small brain size, which show clear cognitive differences between selection lines. To test whether those lines differed in behavioural plasticity, we reared them in groups in structurally enriched environments and then placed adults individually into empty tanks, where we presented them daily with visual predator cues and monitored their behaviour for 20days with video-aided motion tracking. We found that individuals differed consistently in activity and risk-taking, as well as in behavioural plasticity. In activity, only the large-brained lines demonstrated habituation (increased activity) to the new environment, whereas in risk-taking, we found sensitization (decreased risk-taking) in both brain size lines. We conclude that brain size, potentially via increasing cognitive abilities, may increase behavioural plasticity, which in turn can improve habituation to novel environments. However, the effects seem to be behaviour-specific. Our results suggest that brain size likely explains some of the variation in behavioural plasticity found at the intraspecific level.

Physiological differences between winter phenotypes of Siberian hamsters do not correlate with their behaviour

Living in a seasonally changing environment requires periodic, reversible changes in animals' phenotypes to match variations in their abiotic and biotic environments. These changes may relate to temperature regulation, torpor use, basal metabolic rate, body mass or behaviour, all acting in concert to ensure the best adjustment to the environmental challenges. As winter approaches, many small mammals develop a winter phenotype that is qualitatively and quantitatively different from a summer one. However, there is a significant within-population polymorphism in winter phenotype. We hypothesized that winter phenotype is correlated with consistent between-individual differences in animal behaviour, i.e. animal personality, and energy metabolism. We measured basal metabolic rate (BMR) and behavioural traits in three winter phenotypes of Siberian hamsters, Phodopus sungorus, which were acclimated to summer-like and then to winter-like conditions: fully responding, nonresponding and partially responding to a short photoperiod. We found no differences in behavioural traits between hamsters of different winter phenotypes, but the seasonal increase in activity was lowest in full responders indicating their lower behavioural flexibility than partial responders and nonresponders. The same was true for BMR. While nonresponders and partial responders increased their BMR from summer to winter, full responders did not change it. We argue that different winter phenotypes are maintained in the population because they could be beneficial under different environmental conditions. We also suggest that within a population there is a continuum of winter phenotypes, which is not related to differences in animal personalities. This continuum allows for population maintenance despite environmental conditions changing over short and long timescales.

A mechanistic theory of personality-dependent movement behaviour based on dynamic energy budgets.

Consistent between-individual differences in movement are widely recognised across taxa. In addition, foraging plasticity at the within-individual level suggests a behavioural dependency on the internal energy demand. Because behaviour co-varies with fast-slow life history (LH) strategies in an adaptive context, as theoretically predicted by the pace-of-life syndrome hypothesis, mass/energy fluxes should link behaviour and its plasticity with physiology at both between- and within-individual levels. However, a mechanistic framework driving these links in a fluctuating ecological context is lacking. Focusing on home range behaviour, we propose a novel behavioural-bioenergetics theoretical model to address such complexities at the individual level based on energy balance. We propose explicit mechanistic links between behaviour, physiology/metabolism and LH by merging two well-founded theories, the movement ecology paradigm and the dynamic energetic budget theory. Overall, our behavioural-bioenergetics model integrates the mechanisms explaining how (1) behavioural between- and within-individual variabilities connect with internal state variable dynamics, (2) physiology and behaviour are explicitly interconnected by mass/energy fluxes, and (3) different LHs may arise from both behavioural and physiological variabilities in a given ecological context. Our novel theoretical model reveals encouraging opportunities for empiricists and theoreticians to delve into the eco-evolutionary processes that favour or hinder the development of between-individual differences in behaviour and the evolution of personality-dependent movement syndromes.

No male mate choice for female boldness in a bi-parental West African cichlid, the rainbow krib (Pelvicachromis pulcher).

BackgroundIn many species, males have a lower reproductive investment than females and are therefore assumed to increase their fitness with a high number of matings rather than by being choosy. However, in bi-parental species, also males heavily invest into reproduction. Here, reproductive success largely depends on costly parental care; with style and amount of parental effort in several cases being associated with personality differences (i.e., consistent between-individual differences in behaviour). Nonetheless, very little is known about the effect of personality differences on (male) mate choice in bi-parental species.MethodsIn the present study, we tested male mate choice for the level and consistency of female boldness in the rainbow krib, Pelviachromis pulcher, a bi-parental and territorial West African cichlid. Individual boldness was assumed to indicate parental quality because it affects parental defence behaviour. For all males and females, boldness was assessed twice as the activity under simulated predation risk. Mate choice trials were conducted in two steps. First, we let a male observe two females expressing their boldness. Then, the male could choose between these two females in a standard mate choice test.ResultsWe tested for a male preference for behavioural (dis-)similarity vs. a directional preference for boldness but our data support the absence of effects of male and/or female boldness (level and consistency) on male mating preference.DiscussionOur results suggest female personality differences in boldness may not be selected for via male mate choice.

Consistent Between-Individual Differences in Foraging Performance in a Floriphilic Katydid in Response to Different Choices.

The neural constraint hypothesis is one of the central ideas for the understanding of insect-plant interaction but there are still knowledge gaps in the data for foraging behavior and the performance of herbivores, and particularly florivores. We used a floriphilic katydid, Phaneroptera brevis (Serville, 1838) (Orthoptera: Tettigoniidae) and a naturalized weed, Bidens pilosa L. (Asteraceae) in caged experiments in an insectary to answer these questions: 1) How does the foraging performance of the floriphilic katydid vary when exposed to a choice in the number of capitula and types of florets of B. pilosa? 2) Does the foraging performance of the katydid, when exposed to multiple choices, improve with time, and are between-individual differences in foraging performance consistent? We observed that having more choices in the floret types and number of capitula is generally associated with a reduced foraging performance of the katydids. Floret types and number of capitula, however, did not have an interactive effect on foraging performance. We also found that the differences in foraging performance in response to choice tend to be consistent between katydids but each katydid became more efficient and decisive over time. That learning and experience can improve the foraging performance of the katydid has provided us with some insights as to how a continuum of efficient and inefficient katydids can be maintained in a population.

Different or alike? Female rainbow kribs choose males of similar consistency and dissimilar level of boldness

Although the existence of consistent between-individual differences in behaviour (‘personality differences’) has been well documented during the last decade, the adaptive value of such behavioural limitations remains an open field for researchers of animal behaviour. Personalities clearly restrict individuals in their ability to adjust their behaviour to different conditions. However, sheer costs of flexibility cannot explain the polymorphism created by personality variation. In a correlative approach, we here tested whether mate choice might act as a major driving force maintaining personality variation in the monogamous, biparental rainbow krib, Pelvicachromis pulcher. We personality-typed all males and females for their boldness (activity under simulated predation risk) and allowed females to choose between two males that differed in their boldness (behavioural level and consistency). Prior to the choice, females were allowed to observe both males, expressing their natural boldness towards a video-animated natural predator. Both sexes showed personality differences in boldness over the short and long term. Furthermore, when removing side-biased females, we found a disassortative mating preference for the behavioural level and an assortative preference for behavioural consistency in boldness. These preference patterns might facilitate effective parental role allocation during offspring care and/or provide genetic benefits. Our results suggest that sexual selection plays an important role in the evolution of personality differences.

Repeatability and consistency of individual behaviour in juvenile and adult Eurasian harvest mice

Knowledge on animal personality has provided new insights into evolutionary biology and animal ecology, as behavioural types have been shown to affect fitness. Animal personality is characterized by repeatable and consistent between-individual behavioural differences throughout time and across different situations. Behavioural repeatability within life history stages and consistency between life history stages should be checked for the independence of sex and age, as recent data have shown that males and females in some species may differ in the repeatability of behavioural traits, as well as in their consistency. We measured the repeatability and consistency of three behavioural and one cognitive traits in juvenile and adult Eurasian harvest mice (Micromys minutus). We found that exploration, activity and boldness were repeatable in juveniles and adults. Spatial recognition measured in a Y Maze was only repeatable in adult mice. Exploration, activity and boldness were consistent before and after maturation, as well as before and after first sexual contact. Data on spatial recognition provided little evidence for consistency. Further, we found some evidence for a litter effect on behaviours by comparing different linear mixed models. We concluded that harvest mice express animal personality traits as behaviours were repeatable across sexes and consistent across life history stages. The tested cognitive trait showed low repeatability and was less consistent across life history stages. Given the rising interest in individual variation in cognitive performance, and in its relationship to animal personality, we suggest that it is important to gather more data on the repeatability and consistency of cognitive traits.

Food and vitamin D3 availability affects lizard personalities: an experiment

It has been proposed recently that labile state variables (e.g. energy reserves) can have a key role in the development and maintenance of consistent between-individual behavioural variation (i.e. animal personality) within population. In male Carpetan rock lizards (Iberolacerta cyreni), the provitamin D3 component of femoral gland secretion acts as an honest signal in sexual communication. Further, vitamin D3 has many important metabolic functions in reptiles. Therefore, by employing a factorial experiment with food (high vs. low) and vitamin D3 (supplemented vs. control) treatments in wild-caught reproductive male I. cyreni, we tested whether changing labile components of individual state affected (i) behavioural consistency (the degree of between-individual difference) and (ii) behavioural type (mean behaviour). Animal personality in activity was present in all treatments; however, personality was present only in the high food × vitamin D3 supplementation treatment in shelter use and it was present in all but the low food × placebo treatment in risk taking. Lizards (i) decreased activity in the high food treatment, (ii) increased shelter use in the vitamin D3 supplementation treatment and (iii) increased risk taking in the low food × vitamin D3 supplementation treatment. We conclude that short-term changes in individual state affect both behavioural consistency and behavioural type of reproductive male I. cyreni. Unfavourable conditions resulted in decreased behavioural consistency, while high-state individuals became less active in general. Individuals with high specific (vitamin D3) but low general (energy reserves) state took higher risk. We discuss several evolutionary explanations for the reported patterns. The evolutionary and developmental mechanisms resulting in consistent between-individual behavioural differences across time and situations (i.e. animal personality) are of high scientific interest. It has been recently proposed that links between individual state (e.g. how well-fed the individual is) and behaviour can maintain such between-individual differences even on an evolutionarily timescale. However, whether short-term state changes are able to affect animal personality in adults is an open question. In a manipulative experiment, we found that the amount of food and vitamin D3 (known to increase physiological quality and attractiveness of male Carpetan rock lizards, I. cyreni) affected the expression of animal personality and the actual behavioural types of reproductive male Carpetan rock lizards. Therefore, we provide evidence that short-term environmental variation does induce or suppress animal personality, and it also affects individual behaviour.

Tank size alters mean behaviours and individual rank orders in personality traits of fish depending on their life stage

Animals adjust their behaviour over time and contexts to cope with ecological and environmental variation. However, the presence of consistent between-individual differences in behaviour (i.e. personality) suggests that individual behaviour may be less flexible than previously thought. Here, we tested whether the size of the experimental tank and the ontogenetic stage of individuals affect estimates of average and consistent individual variation in activity and risk-taking behaviours in the eastern mosquitofish, Gambusia holbrooki, a fish model widely utilized for behavioural research. We measured risk taking and activity in juvenile, subadult and adult mosquitofish in a standard open-field test, in which the size of test tank varied linearly. We found strong evidence that spatial constraints alter mosquitofish behaviour. In particular, we observed that average activity increased with tank size, while the willingness of fish to take risks was independent of tank size. Moreover, juvenile fish exhibited, on average, lower risk-taking behaviours than older individuals. We highlight that the use of differently sized tanks may result in unequal variation in the average behaviour between juvenile and older fish, with escaping abilities of juvenile fish being underestimated in small environments. Most interestingly, we observed that variation in tank size triggered changes in the individual rank order for both risk taking and activity in juvenile fish, thus altering their personality estimates. In contrast, adult fish maintained consistent individual rank orders across all tank sizes. This study supports the hypothesis that behavioural repeatability increases with age, suggesting that personality estimates on adult animals may be less vulnerable to variation in laboratory contexts than those on juvenile ones.

Plasticity, stereotypy, intra-individual variability and personality: Handle with care

Only recently, variability within individuals has become of importance to evolutionary thinking. The boom in the literature on behavioural variability has led to the emergence of concepts such as behavioural plasticity, stereotypy, imprecision, and intra-individual variability (IIV). The proliferation of new terms has resulted in overlapping concepts, spreading confusion in understanding the origins of variability. Here we provide a critical overview of the concepts related to behavioural variability within the individual. We conclude that although there is no overlapping between behavioural plasticity and IIV, these concepts do overlap with stereotypy; they also face problems with ideas of abnormality and absence of function in stereotyped behaviour. We further provide a critical overview of the sometimes confusing relationship between (1) within individual variability, and (2) consistent variability across individuals (personality). We point out that personality is logically independent of both activational plasticity and IIV, because personality emerges at the population level, whereas plasticity and IIV emerge at the individual level. We conclude that, in personality studies, the failure to acknowledge the existence of either internal variability or consistent between-individual differences in internal variability will result in mixing different phenomena, and inhibit building unified accounts from heterogeneous databases.

Individual differences in behavioral consistency are related to sequential access to resources and body condition in a producer-scrounger game

Investigating the evolution of consistent between-individual behavioral differences necessitates to explain the emergence of within-individual consistency. Relying on a recent mathematical model, we here test the prediction that the emergence of differences in within-individual consistency is related to the sequential access to resources in a frequency-dependent foraging game. To this end we used flocks of zebra finches (Taeniopygia guttata) engaged in a producer-scrounger foraging game. Tactic investment (i.e. the proportion of hops with the head down) significantly predicted successful tactic use (i.e. the proportion of seeds produced). In support of predictions, we found that individuals that arrived first at a foraging area were more consistent in both their investment into and their use of the producer tactic. Also, birds in higher body condition were less consistent in their producer tactic use. These results provide the first evidence that variation in behavioral consistency can emerge through the sequential access to resources in a frequency-dependent game. They also highlight a potential physiological cost of behavioral flexibility. Our findings suggest an explanation for the link between personality traits and social information use.

Boldness and asymmetric contests: role- and outcome-dependent effects of fighting in hermit crabs

Consistent between-individual differences in behavior have been demonstrated in an array of species from diverse taxa, and variation in boldness may be associated with variation in aggressiveness. However, little is known about how boldness is linked with the ability to win fights (resource holding potential) or about how the experience of fighting may alter subsequent boldness. Animal contests often involve role asymmetries, where the 2 opponents fight in different ways. Here, we investigate boldness before and after fighting in attacking and defending hermit crabs during contests over the ownership of gastropod shells. Although prefight boldness did not influence the chance of winning for attackers, successful defenders had longer startle responses (less bold) than those that gave up. Postfight changes in boldness also differed between roles. For defenders, there was a significant decline in consistency of startle responses after fighting, coupled with outcome-dependent plasticity in mean boldness. Furthermore, postfight boldness in defenders varied with the intensity of agonistic behavior inflicted on them by attackers. In contrast, boldness in attackers was stable across the before- and after-fighting situations. Links between internal state and agonistic behavior are known to vary between roles in asymmetric contests. It now appears that similar role-specific links are present between aggression and animal personality.

How does temperature affect behaviour? Multilevel analysis of plasticity, personality and predictability in hermit crabs

When animals are observed on multiple occasions, consistent between-individual differences in behaviour, often referred to as animal personality, may be observed. However, this does not mean that the behaviour of a given individual is readily predictable. While some individuals show low levels of variation around their behavioural mean, others show high levels of variation, and there may be significant between-individual differences in this intraindividual variation (‘IIV’) in behaviour. While it has been suggested that IIV might reduce susceptibility to predators, little is known about the functions or causation of IIV. We investigated the effects of temperature on the startle response duration of hermit crabs, Pagurus bernhardus. For poikilothermic animals, temperature has a direct and multiplicative influence on metabolic rate, which in turn is expected to influence behaviour because of its effect on energy requirements. At the level of mean startle response durations, the effect of temperature was dependent on treatment order; within treatment orders, individuals showed different reaction norms. In contrast, at the level of IIV, while the presence of significant between-individual differences was dependent on treatment order, there was a clear unidirectional effect in both treatment orders for individuals to be less predictable at higher temperature. Thus, predictability in behaviour appears to vary with a key environmental variable that is known to influence energy requirements and potentially the level of risk that individuals are willing to accept.