Abstract: Despite increasing interest, animal personality is still a puzzling phenomenon. Several theoretical models have been proposed to explain intraindividual consistency and interindividual variation in behaviour, which have been primarily supported by qualitative data and simulations. Using an empirical approach, I tested predictions of one main life-history hypothesis, which posits that consistent individual differences in behaviour are favoured by a trade-off between current and future reproduction. Data on life-history were collected for individuals of a natural population of grey mouse lemurs (Microcebus murinus). Using open-field and novel-object tests, I quantified variation in activity, exploration and boldness for 117 individuals over 3 years. I found systematic variation in boldness between individuals of different residual reproductive value. Young males with low current but high expected future fitness were less bold than older males with high current fecundity, and males might increase in boldness with age. Females have low variation in assets and in boldness with age. Body condition was not related to boldness and only explained marginal variation in exploration. Overall, these data indicate that a trade-off between current and future reproduction might maintain personality variation in mouse lemurs, and thus provide empirical support of this life-history trade-off hypothesis.

Abstract: We tested whether boldness is associated with attenuation of the physiological stress response in behaviorally selected lines of zebrafish Danio rerio. We measured three component behaviors of boldness: cortisol levels under control and stressed conditions, growth rate, and expression of key genes linked to the hypothalamic-pituitary-interrenal axis in the brain. Surprisingly, bold animals did not differ from shy animals with respect to cortisol levels. However, significant differences between these animals in the expression of glucocorticoid receptors and genes that regulate production of stress hormones indicate that there may still be a relationship between bold behavior and the stress axis. Perhaps the most surprising result of this study was the degree of sexual dimorphism: female zebrafish were bolder than male zebrafish, had significantly lower levels of cortisol, and differed significantly in the expression of several genes in the brain. Our data indicate that a bold behavioral type is ass...

Abstract: The animal personality literature uses three approaches to assess personality. However, two of these methods, personality ratings and experimentation, have been little compared in captivity and never compared in the wild. We assessed the boldness of wild chacma baboons Papio ursinus using both ratings and experimental methods. Boldness was experimentally assessed when individuals were presented with a novel food item during natural foraging. The boldness of the same individuals was rated on a five-point scale by experienced observers. The ratings and experimental assessments of boldness were found to correlate positively and in a linear fashion. When considered categorically the two approaches showed variable agreement depending on the number of categories assigned and the cut-off criteria adopted. We suggest that the variation between approaches arises because each method captures different aspects of personality; ratings consider personality in absolute terms (using predefined criteria) and multiple contexts, while experimental assessments consider personality in relative terms (using experimental scores relative to the population average) and in limited contexts. We encourage animal personality researchers to consider adopting both methodologies in future studies. We also propose that future studies restrict their analyses to continuous data, since the greatest comparability between methods was found with these data. However, if individuals must be categorised, we suggest that researchers either (a) analyse only those individuals categorised as bold or shy by both ratings and experimental approaches or, if these methods cannot be employed simultaneously, (b) do not use approach-specific criteria but choose a cut-off that can be compared by both approaches.

Abstract: Sexual cannibalism particularly before mating is costly for the male victim but also for the female aggressor if she risks remaining unmated. The aggressive spillover hypothesis explains the persistence of this behavior as a maladaptive side effect of positive selection on aggressiveness in a foraging context. The hypothesis predicts that the occurrence of sexual cannibalism is explained by female aggressiveness but is not related to male phenotype or behavioral type. An alternative hypothesis invokes sexual selection and makes the opposite prediction namely that sexual cannibalism is an expression of female choice and should hence mainly target males of low quality. We tested the above hypotheses on a sexually dimorphic nephilid spider Nephilengys livida, known for male monopolization of females via genital damage, female genital plugging, and mate guarding, by staging mating trials during which we recorded mating behaviors and occurrences of pre- and postcopulatory cannibalism. We did not restrict assessment of aggressiveness to the mating and foraging context but also included aggression against same sex conspecifics. To assess female personalities, i.e., consistent individual differences in behavior including aggressiveness, we repeatedly tested them for intra-sex aggression, voracity towards prey, locomotory activity, and boldness. Females exhibited consistent differences in intra-sex aggressiveness, latency to attack prey, and boldness. Aggressive females had shorter latencies to attack prey and were more active than non-aggressive ones. In contrast to the predictions of the aggressive spillover hypothesis, females that were aggressive towards prey and towards other females were not more likely to attack a male than non-aggressive females. In support of the mate choice hypothesis, less aggressive males were more likely attacked and cannibalized than more aggressive ones. This hints at sexual selection for aggressiveness in males and raises the question of mechanisms that maintain variation in male aggressiveness.

Abstract: There is a growing interest in animal personality because individual variation is the substrate of the evolutionary process. Despite revelations that personality traits affect key fitness variables, little is known about the proximate mechanisms generating consistent behavioural differences between individuals. Boldness, the propensity to take risks, is one of the most widely studied aspects of personality in fishes. We assessed the position of juvenile Argyosomus japonicus on the “boldness–shyness” continuum by repeatedly recording the time taken to exit a refuge and explore a novel environment. Stress-related hormone concentrations after exposure to a mild stressor were analysed 1 month before behavioural assays and found to be significantly linked to boldness scores. Shy fish had significantly higher plasma cortisol concentrations in response to handling stress than bold fish. Spontaneous switching between personality categories occurred between trials, highlighting the importance of repeated testing of personality traits over time to correctly attribute personality.

Abstract: To showcase the importance of genotype × environment interactions and the presence of predation risk in the experimental assessment of boldness in fish, we investigated boldness in terms of feeding behavior and refuge use in two genetically different populations of juvenile carp (Cyprinus carpio) in two replicated experimental conditions in ponds and laboratory tanks. The populations were expected to exhibit genetic differences in boldness due to differential evolutionary adaptation to low-predation-risk pond aquaculture conditions. Boldness was measured in variants of open-field trials with and without implementation of additional predation risk-stimuli by angling on feeding spots. Without explicit implementation of risk, genotypes adapted to low-risk environments, i.e., domesticated mirror carp behaved consistently bolder than their less domesticated scaled conspecifics in the pond environment, but not in the laboratory environment. When we implemented artificial risk-stimuli by angling on previously safe feeding spots, boldness differences among genotypes also emerged in the laboratory environment, indicating strong genotype × environment effects on boldness behavior of carp. The expected genetic basis of boldness differences among genotypes was clearly supported in the pond environment, while the laboratory study revealed these patterns only under inclusion of explicit risk-stimuli. Our study thus underscores that boldness may involve both a basal component that is expressed independently of obvious predation risk (e.g., in open fields) and a component revealed in relation to explicit predation risk, and both dimensions may respond differently in behavioral tests.

Abstract: It is becoming clear that individual animals exhibit behaviours that are repeatable, consistent and predictable across various contexts and time, and that may be correlated to form behavioural syndromes. The influence of parasitism on host behaviour, although well-documented, is only now being examined in a multi-trait context, and behavioural syndromes provide a framework for such investigations. We test the hypothesis that parasites modify host behavioural syndromes by quantifying the relationship between infection by four trematode species and the correlations, repeatability and consistency of three host behaviours (activity, aggression and boldness) in a freshwater fish, Gobiomorphus cotidianus, in the presence and absence of a predator odour. There was a significant correlation between activity and aggression, and both these behaviour showed higher values in the presence of a chemical predator cue. Of the behaviours tested, only aggression responses were significantly related to infection with one of the parasites, Apatemon sp. Activity, aggression and boldness scores were repeatable across test sessions, but much less so in the presence of a predator cue. Interestingly, individual-level consistency in activity and aggression was significantly associated with infection by Telogaster opisthorchis, Deretrema philippae and/or Apatemon sp., with the direction of the association depending on the behaviour tested. These findings suggest that behavioural syndromes may not only be targets for adaptive host manipulation by parasites, but also that, even if through mere pathology, parasites could act as external agents generating variation in behavioural syndromes.

Abstract: Although the occurrence of individuals' behavioral differences in a "shyness–boldness" continuum (i.e., animals' propensity to take risks) is well established from experimental studies, little is known about how this personality trait might influence individual predation risk management decisions in natural systems. We recorded the risk management strategies (RMS) of a natural population of redshanks by observing the daily behavioral decisions made by foraging individuals. These included proximity to neighbors, flock size, position with respect to predator concealing cover, and vigilance. Using hierarchical mixed effects models, we found that although variation in most of these RMS had a significant individual component, only vigilance was moderately repeatable and therefore a personality trait. There was no evidence for a behavioral risk management syndrome: there were no significant correlations of vigilance with aggressiveness or exploratory behavior. Vigilance levels were highly flexible, were adjusted to the riskiness of the situation, and individuals varied in the degree of this plasticity, suggesting that a redshank's boldness (personality) may only contribute a small amount to natural risk management and that it is situation dependent. This emphasizes that although variable risk and profitability in the environment may select for different personalities (e.g., that determine baseline levels of vigilance all things being equal), these baseline levels can be modified greatly through behavioral flexibility when individuals are confronted by a change in environmental context, potentially removing these differences.

Abstract: Population density regulates the strength of intraspecific competition and may thereby be reflected in life-history variables, such as development time, growth rate, or investment in immune defense. However, population density may also affect the fitness payoffs of different behaviors and consequently shape the development of personality. Here we studied if population density during nymphal development (one, four, or ten individuals raised together) affects the level of boldness, measured as the latency time to recover from freezing and emerge from a shelter, aggressiveness towards conspecifics or their correlation at the adult stage in the field crickets, Gryllus integer. In addition, we tested if individuals invest more resources in immune function or speed up their development in response to a high conspecifics density during ontogeny. Nymphal density did not affect adult boldness or aggressiveness towards conspecific males per se, but these variables showed a negative association, i.e., indicated an unconventional behavioral syndrome in the highest density treatment. Supporting the effectiveness of density treatments in inducing plastic responses, individuals reached maturity sooner and invested more resources in immune function in the highest nymphal density group compared to groups consisting of one or four individuals. Our results suggest that population density may play an important role in shaping both the realized life history and development of behavioral syndromes.

Abstract: Individuals foraging in groups constantly need to make decisions, such as when to leave a group, when to join a group, and when to move collectively to another feeding site. In recent years, it has become evident that personality may affect these foraging decisions, but studies where individuals are experimentally forced into different roles are still absent. Here, we forced individual barnacle geese, Branta leucopsis, differing in boldness scores, either in a joining or in a leaving role in a feeding context. We placed a food patch at the far end of a test arena and measured the arrival latency and number of visits of individuals to the patch either in the presence of a companion that was confined near the food patch (“joining context”) or in the presence of a companion that was confined away from the food patch (“leaving context”). We also ran trials without a companion (“nonsocial context”). Bolder individuals arrived more quickly than shyer individuals in the “leaving” context, but there was no effect of boldness in the “joining” context, suggesting that boldness differences are important in explaining variation in leaving behavior but not in joining behavior. The difference in arrival latency between the “joining” and non-social context increased with decreasing boldness score, suggesting that shyer individuals are more responsive to the presence of other individuals (i.e., social facilitation). These results indicate that individual differences in boldness play a role in patch choice decisions of group-living animals, such as when to leave a flock and when to join others at a patch.

Abstract: Summary 1. Populations of the same species often display different behaviours, for example, in their response to predators. The question is whether this difference is developed as part of a divergent selection caused by differences in predation pressure, or as a result of phenotypic responses to current environmental conditions. 2. Two populations of Eurasian perch were investigated over a time span of 6 years to see whether risk-taking behaviour in young-of-the-year perch were consistent across cohorts, or if behaviour varied over time with changes in predation regime. 3. Boldness was estimated in aquarium studies by looking at how the fish made trade-offs between foraging in a risky area and staying in shelter. Predation risk of each year and lake was estimated from fishing surveys, using an individual-based model calculating attack rates for cannibalistic perch.

Abstract: Behavioral syndromes often have individuals varying along a continuum of personality traits. Some individuals exhibit bold or aggressive behaviors and are willing to explore novel stimuli, whereas others are shy and tend to avoid novel stimuli. Species that undergo an ontogenetic diet shift may experience a particularly important benefit if the shift to more-profitable prey is linked to this willingness to explore novel stimuli. However, actively selecting more-evasive prey can make these predators more vulnerable to predation themselves. We used largemouth bass Micropterus salmoides as a model to examine the role of behavioral syndromes in structuring predator strategies for dealing with these conflicting environmental pressures. Exploration behavior was first determined by testing willingness to explore a novel environment. Behaviors were then measured in two other contexts where exploration and boldness could potentially have fitness consequences: (1) the likelihood of consuming a novel prey i...

Abstract: Variation among individuals in the expression of behaviors and associations of behaviors in different contexts can lead to the maintenance of behavioral polymorphisms. Individual variation in morphology is often associated with behavioral polymorphism, yet the degree to which morphology predicts behavioral phenotype is not well understood. We measured individual variation in size and behaviors in the sailfin molly, Poecilia latipinna, by comparing the behavior of individual males of different sizes across four different contexts (mating, exploratory tendency, sociability, and predator inspection). We also investigated the degree to which male size, a fixed genetic trait, influenced the expression of each behavior and associations between behaviors. We found that male mollies show strong associations between certain behaviors and only some of these are predicted by male size. For example, size has a strong influence on the courtship-boldness axis with larger males showing higher rates of courtship displays and being bolder in predator inspection. A positive association was found between exploratory tendency, sociability, and gonopodial thrusting rates, yet the expression of these behaviors was independent of male size. Thus, sailfin mollies, like many fish species, show associations of behaviors that contribute to differences among males in personality type. The fixed genetic effect of male size at maturity influences courtship and boldness, but individual variation in exploratory tendency, sociability, and sneak copulation attempts through gonopodial thrusts is independent of male size. Such variation among males in behavioral associations within and between different contexts may slow the rate at which populations of P. latipinna can diverge in individual behaviors.

Abstract: Many animal species exhibit behavioural syndromes, groups of two or more behaviours that are linked together across different environments or time points. Behavioural syndromes give rise to stable behavioural profiles and have been likened to personality in humans. However, the proximate causes (or mechanisms) that underlie the clustering of behaviour are not well understood. In this review, we examine the proximate causes of the aggression-boldness behavioural syndrome, which constitutes a positive correlation between aggression, boldness and exploratory activity. In particular, we will focus on novel insights that have been gained from zebrafish, a genetically tractable behavioural model which can be used to study the mechanistic basis of behaviour. Studies of the proximate causes of behavioural syndromes provide us with the opportunity to understand the clustering of behaviours — and perhaps even the basis of personality — at the molecular level. Thus, this exciting field not only promises to bring novel insights into animal behaviour, but also forces us to rethink our own personalities as well.

Abstract: Recent theory predicts that personality traits contributing to resource intake rates could reflect the individual's condition-dependent capacity to resist parasites and pathogens. Since females often prefer mates with strong immune defence, females could potentially gain fitness benefits by using male's behavioral type (BT) as one mate choice criteria. We studied if female field crickets base their mate choice on male boldness and if the boldness would predict survival under challenge to opportunist pathogen Serratia marcescens. In addition, we tested if three different females would prefer the same males. Boldness did not explain individual's lifespan in experimental infection. All the three females preferred one male within pair over the other male in 26.9% of the mate choice tests, but the preferred male varied between the females. Our results suggest that females show preferences for bold BTs, but that male boldness may not reflect his capacity to resist bacterial pathogens.

Abstract: Individual differences in behavioural traits may play a role in reproductive behaviour and it is likely that different personality types have different reproductive success across specific social environments. This suggests a role for sexual selection for personality types, including a link between behavioural traits and alternative reproductive tactics. While research on morphological differences between guarders (bourgeois males defending resources) and sneakers (males parasitizing the territories of bourgeois males) is well characterized, the role of personality in the adoption of alternative mating tactics has hitherto been largely ignored. We investigated individual behavioural differences in a sneaker‐guarder mating system using size/age-matched males of a small freshwater fish, the European bitterling (Rhodeus amarus). We predicted distinct behavioural responses by guarder and sneaker males that were consistent in different contexts, indicating the existence of behavioural syndromes associated with male mating tactic. No behavioural syndromes were detected in male R. amarus, despite ability of individual male bitterling to establish dominance, boldness and investment in sperm competition being relatively repeatable across three consecutive trials. Male aggression, though not repeatable, was negatively correlated with the number of ejaculations, indicating a trade-off between aggression and sperm loading. No association between the tendency of males to guard a territory and behavioural traits was found, despite a significant association between the tendency to guard and morphological and physiological traits, with higher relative testis size and more breeding tubercles in guarder males. Our data suggest male bitterling mating tactics are largely unconstrained by innate factors and likely to be the product of prevailing environmental and social conditions.

Abstract: Consistent individual behavioral differences across ecological contexts are a recognized feature of animal populations. These differences can be expressed in two ways: context-specifically or context-generally. The former is characterized by consistent responses in one context (i.e. repeatability), whereas the latter by consistency that spans contexts (i.e. behavioral syndromes). The proximate causes of behavioral consistency remain unclear, yet there is evidence that physiology may couple the expression of some behavioral traits in unrelated contexts. We therefore explored the correlation between bold behavior of female sand fiddler crabs (Uca pugilator) and the condition of the hepatopancreas, an organ vital to crustacean metabolism and reproduction. We did this by taking replicate measurements of two risk-taking behaviors per individual in the contexts of predator avoidance and environment exploration, and examining correlations within and between these observations. We then determined the relationship of behavior with hepatopancreas mass and lipid content. Individual crabs responded consistently within each context. However, across-context correlations were absent, indicating that boldness is isolated, at least in the selected scenarios. Additionally, anti-predator and exploratory behaviors were significantly influenced by size but not linked to hepatopancreas physiology. Our results show that context-specific trait expression may occur in the absence of a physiological correlate.

Abstract: A major axis of inter-individual behavioral variation is correlated behavioral traits, known variously as behavioral syndromes, personality, or temperament. The zebra fi sh is a good model organism with which to explore the molecular genetic mechanisms of personality. The fi rst step in the study of behavioral syndromes is development of reliable assays for sorting fi sh along an axis of behavioral variation. Here, we describe an assay for measuring exploratory tendency, which is linked to boldness in the face of predation threat, thus forming a exploratory-boldness behavioral syndrome. Ten fi sh were placed in the fi rst of a series of fi ve chambers connected by narrow-diameter lengths of PVC tubing, presenting, in essence, a serial openfi eld test for tendency to explore novel areas. Some individuals passed through the tunnels to explore the next chamber while some individuals were reluctant to do so. After 7 days, individuals in the last two chambers were designated as exploratory, while individuals that remained in the fi rst two chambers were designated as nonexploratory. These fi sh were then transferred individually to a predator-inspection apparatus containing a large adult convict cichlid (potential predator) behind a mesh partition. Exploratory zebra fi sh moved less and spent more time near the predator than nonexploratory individuals did. Thus, the multi-chamber exploration openfi eld test was a useful assay for scoring zebra fi sh along an exploratoryboldness behavioral syndrome. The serial openfi eld test has been modi fi ed to sort 2-week-old larvae, which opens the door to mass-screening of mutagen-treated embryos.