Consistent Individual Differences In Behaviour Research Articles

Reproductive state but not recent aggressive experience influences behavioral consistency in male Siamese fighting fish

Consistent individual differences in behavior imply that individuals act in the same manner every time they encounter a situation while differing from others. While these differences occur in a variety of contexts in a wide range of organisms, how recent experience affects behavioral consistency remains underexplored. Male Siamese fighting fish exhibit consistent individual differences in behavior when both a male and a female are present. However, whether these responses can be shaped by immediate recent aggressive experience is unknown. In this study, males first were presented with paired dummy male and female conspecifics after they had been isolated to obtain a baseline, no-experience measure. Males then won and lost fights and were retested with the dummies after each fight. These three experience types (no, win, loss) occurred both when males did and did not have nests to determine the effects of nest presence, experience, and the interaction between these factors on behavioral consistency. Overall behavior did not change based on experience with the exception of male-directed tail beats. Repeatability values were affected more by having a nest than fight outcome. This study demonstrates that consistent individual differences in behavior to conflicting stimuli are fairly resistant to short-term aggressive experiential effects.

Individual and Sex Differences in Habituation and Neophobia in House Sparrows (Passer domesticus)

AbstractHeterogeneity in the environment favours foragers that are flexible (phenotypically plastic). However, consistent individual differences in behaviour (personality), such as in risk‐taking, might affect an individual's ability to find food, avoid predators and adjust to new conditions. It is now well known that personalities exist in many taxa, but much less is known about individual variation in plasticity. We measured the tendency to begin foraging across different levels of risk in house sparrows (Passer domesticus), using a behavioural reaction norm framework to simultaneously assess personality and plasticity. We asked whether individuals were consistently different across risk levels, and whether they differed in habituation and neophobia, both of which were treated as cases of plasticity. We found that males habituated more than females by beginning to feed sooner after repeated instances of a human disturbance in the presence of an initially unfamiliar object. Individuals of both sexes also exhibited consistent differences across trials, but did not differ in the rate of habituation beyond the difference between the sexes. When a novel object was placed in the foraging area, both sexes exhibited similar degrees of neophobia by delaying feeding. The magnitude of this change varied among birds, indicating individual differences in neophobia. Our results indicate that both personality and individual variation in plasticity exist but should be treated as independent phenomena. The presence of variation in plasticity implies that the raw material necessary for selection on neophobia exists, and that if heritable, plasticity in risk‐taking across contexts could evolve.

Personality differences are related to long-term stress reactivity in a population of wild eastern chipmunks, Tamias striatus

Consistent individual behavioural differences in exploration, docility and boldness are often correlated and are associated with differences in short-term neurophysiological responses to environmental perturbations in many animal species. These physiological mechanisms are much less studied over longer periods in wild populations. Here we report the relationships among exploration, docility measured in open-field tests and trappability, taken as an index of boldness, in a wild population of eastern chipmunks and investigate whether behavioural differences among individuals are associated with differences in autonomic nervous system reactivity. We also assess the cortisol level of individuals over several months to investigate whether chipmunks with different exploration levels display different mean cortisol levels or differences in their cortisol variability. Open-field tests showed consistent individual differences in exploration patterns (ranging from fast to slow). Faster explorers were less docile when handled and were trapped more often (males) or farther from their burrows (females) than slower explorers. Fast explorers also showed a higher sympathetic activity under restraint but more stable cortisol levels over the course of the active season, suggesting a lower hypothalamo–pituitary–adrenal reactivity. Our results show that chipmunks display individual behavioural variation and that these differences may have physiological implications over long periods in natural settings. Future studies should investigate the fitness consequences of such behavioural/physiological differences.

Personality in social insects: How does worker personality determine colony personality?

Abstract Social insect colonies and the workers comprising them, each exhibit consistent individual differences in behavior, also known as ‘personalities’. Because the behavior of social insect colonies emerges from the actions of their workers, individual variation among workers’ personality may be important in determining the variation we observe among colonies. The reproductive unit of social insects, on which natural selection acts, is the colony, not individual workers. Therefore, it is important to understand what mechanisms govern the observed variation among colonies. Here I propose three hypotheses that address how consistent individual differences in the behavior of workers may lead to consistent individual differences in the behavior of colonies: 1. Colonies differ consistently in their average of worker personality; 2. The distribution but not the average of worker personalities varies consistently among colonies; and 3. Colony personality does not emerge from its worker personality composition but from consistent external constraints. I review evidence supporting each of these hypotheses and suggest methods to further investigate them. The study of how colony personality emerges from the personalities of the workers comprising them may shed light on the mechanisms underlying consistent individual differences in the behavior of other animals.

Correlating context-specific boldness and physiological condition of female sand fiddler crabs (Uca pugilator)

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.

Are personality differences in a small iteroparous mammal maintained by a life-history trade-off?

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.

Low heritabilities, but genetic and maternal correlations between red squirrel behaviours

Consistent individual differences in behaviour, and behavioural correlations within and across contexts, are referred to as animal personalities. These patterns of variation have been identified in many animal taxa and are likely to have important ecological and evolutionary consequences. Despite their importance, genetic and environmental sources of variation in personalities have rarely been characterized in wild populations. We used a Bayesian animal model approach to estimate genetic parameters for aggression, activity and docility in North American red squirrels (Tamiasciurus hudsonicus). We found support for low heritabilities (0.08-0.12), and cohort effects (0.07-0.09), as well as low to moderate maternal effects (0.07-0.15) and permanent environmental effects (0.08-0.16). Finally, we found evidence of a substantial positive genetic correlation (0.68) and maternal effects correlation (0.58) between activity and aggression providing evidence of genetically based behavioural correlations in red squirrels. These results provide evidence for the presence of heritable variation in red squirrel behaviour, but also emphasize the role of other sources of variation, including maternal effects, in shaping patterns of variation and covariation in behavioural traits.

Mate quality, not aggressive spillover, explains sexual cannibalism in a size-dimorphic spider

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.

No evidence for negative frequency-dependent feeding performance in relation to personality

An increasing number of studies report the presence of consistent individual differences in behavior and/or physiology over time and context, known as animal personality. A pivotal question in animal personality research concerns the mechanism(s) responsible for its evolution and maintenance. Negative frequency–dependent selection is considered to be one of these important mechanisms, although evidence for this is largely absent. Here, we studied whether the feeding performance of barnacle geese was negative frequency-dependent in a producer–scrounger game. We studied the feeding time of one bold or one shy individual in groups consisting of only bold or shy companions to study if the rare type in the group performs best. A previous study with this species showed that scrounging increased with shyness. Hence, we expected shy individuals to do better in the presence of bold companions due to the increased scrounging opportunity and bold individuals to do better in the presence of shy companions as there were ample opportunities to produce food. We found no evidence for negative frequency–dependent feeding success; rather, we found that, independent of their boldness score, all individuals enjoyed higher feeding success when foraging with bold than with shy companions. The higher foraging success of individuals foraging with bold companions is explained by a higher joining proportion in the presence of bold companions. Our results provide no evidence for negative frequency– dependent feeding success in barnacle geese but indicate that both bold and shy individuals can increase their foraging returns

Short-term exposure to an endocrine disruptor affects behavioural consistency in male threespine stickleback

It has been established that exposure to xenooestrogens can have profound effects on reproductive and aggressive behaviours in aquatic organisms. Studies on the effects of 17α-ethinyloestradiol (EE2) on behaviour, however, rarely examine these effects over multiple trials, across time, or across contexts. In addition, it is possible that individuals vary in their sensitivity to EE2 and individuals may differ in the degree to which their behaviour is affected. The study of consistent individual differences in behaviour has grown in popularity in recent years perhaps because of the evolutionary questions this behavioural variation raises. Adult male threespine stickleback ( Gasterosteus aculeatus) from an anadromous population repeatedly received the simultaneous presentation of a dummy male and dummy female conspecific both before and after exposure to a short-term, nominal (15 ng L −1) concentration of 17α-ethinyloestradiol (EE2). These before and after measures were then compared against one another as well as against responses of males in a control group that was not exposed to EE2. Courtship, aggression, and nesting behaviours were all affected by EE2 exposure. In addition, behavioural consistency over trials was markedly reduced after EE2 exposure, as shown by lower repeatability values in the after exposure measures and in weaker correlations between the before and after exposure measures in the EE2 group compared to the control group. This suggests that male threespine stickleback vary in their sensitivity to EE2. This study is one of the first to examine the effects of short-term EE2 exposure on behaviour across trials and has important implications for population-level fitness consequences of xenooestrogens.

Persistent individual differences in tactic use in a producer–scrounger game are group dependent

Consistent individual differences in behaviour have now been documented in a broad range of organisms over a variety of contexts. However, individual differences in social contexts have received less attention. We explored the consistency and temporal persistence of individual differences in tactic use in a producer–scrounger foraging game using two sets of flocks of wild-caught nutmeg mannikins, Lonchura punctulata. With both sets of birds, we observed significant individual differences in tactic use that persisted under different food distributions and when flock members were reunited at a 6-month interval with the same flockmates but not when flock members were different. In another experiment, in which birds with high-scrounging profiles were made to forage in the same flock, the corporate frequency of scrounging was no higher, and the intake rate no lower than in flocks made up of intermediate- or low-frequency scroungers. Taken together our experiments suggest that persistent individual differences can arise from dynamics that are peculiar to the group in which they occur, underlining the importance of companions’ identity in determining tactic use in this game. Behavioural plasticity can erase idiosyncratic individual differences in games with frequency-dependent payoffs when group composition changes.

Individual variation in helping in a cooperative breeder: relatedness versus behavioural type

Helpers in cooperatively breeding groups can vary hugely in the variety and level of care they provide. Several studies suggest that kin selection alone cannot be invoked to explain variation in helping for many species, but there have been few explicit tests of this under controlled conditions. Here, we investigated whether relatedness to the breeding pair or consistent individual differences in behaviours explained variation in helping by the cooperatively breeding cichlid Neolamprologus pulcher . We established standardized social groups consisting of a breeding pair and one related ( r = 0.5) and one unrelated ( r = 0) helper. Two forms of helping, territory maintenance and territory defence, were measured repeatedly under controlled conditions: helping was variable between, but consistent within, individuals. Furthermore, there was some evidence that helpers that carried out more maintenance also performed more defence. Contrary to the kin selection hypothesis, relatedness did not predict the amount or variety of helping executed. Risk responsiveness, activity levels and aggressiveness were repeatable within individuals, so constituted ‘behavioural types’ (or personality traits), but were uncorrelated with each other. More aggressive, risk-prone or more active helpers participated in more territory defence than submissive, risk-averse or inactive helpers. Risk-prone individuals contributed more to territory maintenance than risk-averse helpers. Overall, differences in behavioural type, rather than relatedness, explained most variation in helping behaviour in N. pulcher . This study highlights the importance of considering consistent individual differences in behaviour for predicting participation and performance in complex social interactions.

High In Situ Repeatability of Behaviour Indicates Animal Personality in the Beadlet Anemone Actinia equina (Cnidaria)

‘Animal personality’ means that individuals differ from one another in either single behaviours or suites of related behaviours in a way that is consistent over time. It is usually assumed that such consistent individual differences in behaviour are driven by variation in how individuals respond to information about their environment, rather than by differences in external factors such as variation in microhabitat. Since behavioural variation is ubiquitous in nature we might expect ‘animal personality’ to be present in diverse taxa, including animals with relatively simple nervous systems. We investigated in situ startle responses in a sea anemone, Actinia equina, to determine whether personalities might be present in this example of an animal with a simple nervous system. We found very high levels of repeatability among individuals that were re-identified in the same locations over a three week sampling period. In a subset of the data, where we used tide-pool temperature measurements to control for a key element of variation in microhabitat, these high levels of repeatability remained. Although a range of other consistent differences in micro-habitat features could have contributed to consistent differences between the behaviour of individuals, these data suggest the presence of animal personality in A. equina. Rather than being restricted to certain groups, personality may be a general feature of animals and may be particularly pronounced in species with simple nervous systems.

Variation in personality and behavioural plasticity across four populations of the great tit Parus major

1. Interest in the evolutionary origin and maintenance of individual behavioural variation and behavioural plasticity has increased in recent years. 2. Consistent individual behavioural differences imply limited behavioural plasticity, but the proximate causes and wider consequences of this potential constraint remain poorly understood. To date, few attempts have been made to explore whether individual variation in behavioural plasticity exists, either within or between populations. 3. We assayed 'exploration behaviour' among wild-caught individual great tits Parus major when exposed to a novel environment room in four populations across Europe. We quantified levels of individual variation within and between populations in average behaviour, and in behavioural plasticity with respect to (i) repeated exposure to the room (test sequence), (ii) the time of year in which the assays were conducted and (iii) the interval between successive tests, all of which indicate habituation to novelty and are therefore of functional significance. 4. Consistent individual differences ('I') in behaviour were present in all populations; repeatability (range: 0.34-0.42) did not vary between populations. Exploration behaviour was also plastic, increasing with test sequence - but less so when the interval between subsequent tests was relatively large - and time of year; populations differed in the magnitude of plasticity with respect to time of year and test interval. Finally, the between-individual variance in exploration behaviour increased significantly from first to repeat tests in all populations. Individuals with high initial scores showed greater increases in exploration score than individuals with low initial scores; individual by environment interaction ('I × E') with respect to test sequence did not vary between populations. 5. Our findings imply that individual variation in both average level of behaviour and behavioural plasticity may generally characterize wild great tit populations and may largely be shaped by mechanisms acting within populations. Experimental approaches are now needed to confirm that individual differences in behavioural plasticity (habituation) - not other hidden biological factors - caused the observed patterns of I × E. Establishing the evolutionary causes and consequences of this variation in habituation to novelty constitutes an exciting future challenge.

RETRACTED ARTICLE: Individual- and condition-dependent effects on habitat choice and choosiness

Research on consistent individual differences in behavior, or “behavioral syndromes”, continues to grow rapidly, and yet, the aspects of behavior under consideration have remained remarkably limited. Here, we consider individual variation in consistency of choice (termed here “choosiness”), as expressed during habitat choice. We repeatedly tested the responses of female Western Black Widows, Latrodectus hesperus, to two cues of habitat quality: prey chemical cues and variation in web site illuminance. We estimated females’ response by the distance they positioned themselves from (1) the source of prey chemical cues and (2) the darkest edge of our test arena. Individuals with low variance in their responses are deemed more “choosy”, whereas individuals with high variance are deemed less “choosy”. Generally, most females initiated web construction near the source of the prey chemical cues and tended to place themselves in low-light conditions. However, we detected strong, repeatable differences in females’ intensity of response, and within-individual variance of response (i.e., choosiness) was correlated across situations: females with highly consistent responses towards cricket chemical cues also exhibited highly consistent responses towards variation in light conditions. When deprived of food for extended periods, females were indistinguishable in their responses towards prey chemical cues, but tended to initiate web construction in brighter lighting conditions. Food-deprived females universally exhibited higher variance and diminished consistency in their responses (i.e., they were less choosy). Additionally, higher choosiness was associated with greater mass loss during choice trials, suggesting choosiness is energetically costly. Our results demonstrate that consistency of response to environmental cues is yet another element of behavior that varies among individuals and variation in choosiness could beget speed/quality trade-offs during animal decision making.

Ontogenetic immune challenges shape adult personality in mallard ducks.

Consistent individual differences in behaviour are widespread in animals, but the proximate mechanisms driving these differences remain largely unresolved. Parasitism and immune challenges are hypothesized to shape the expression of animal personality traits, but few studies have examined the influence of neonatal immune status on the development of adult personality. We examined how non-pathogenic immune challenges, administered at different stages of development, affected two common measures of personality, activity and exploratory behaviour, as well as colour-dependent novel object exploration in adult male mallard ducks (Anas platyrhynchos). We found that individuals that were immune-challenged during the middle (immediately following the completion of somatic growth) and late (during the acquisition of nuptial plumage) stages of development were more active in novel environments as adults relative to developmentally unchallenged birds or those challenged at an earlier developmental time point. Additionally, individuals challenged during the middle stage of development preferred orange and avoided red objects more than those that were not immune-challenged during development. Our results demonstrate that, in accordance with our predictions, early-life immune system perturbations alter the expression of personality traits later in life, emphasizing the role that developmental plasticity plays in shaping adult personality, and lending support to recent theoretical models that suggest that parasite pressure may play an important role in animal personality development.

Personality affects zebra finch feeding success in a producer–scrounger game

Recent evidence strongly suggests that natural selection can favour the evolution of consistent individual differences in behaviour ('personalities'). Indeed, personality shows heritable variation and has been linked to fitness in many species. However, the fitness effects of personality are highly variable within and between species. Furthermore, the nature of the causal influence of personality on an organism's fitness remains unclear so far. Competition has been proposed as a factor modulating this relationship. Thus, personality has been found to affect individual success in competition by interference in a few species, but its influence in scramble competition remains unexplored. We assessed exploratory tendencies (thought to be a key component of personality) in a model species, the zebra finch, Taeniopygia guttata. In a first session, we formed foraging flocks composed of four individuals with different exploration scores, and allowed them to play producer-scrounger games repeatedly. During a second session, individuals were reassigned to different flocks to check for consistency in the influence of exploratory tendency across different social contexts. Exploratory tendency influenced individual feeding success during the first session but not during the second one. High-exploratory birds were less successful at finding food (i.e. playing the producer tactic) and consequently had a lower feeding success, but were presumably able to adjust their behaviour between sessions. We discuss our results in relation to the interactive effects of both personality and experience, and highlight the role of competition processes on the evolution of personality.

Coping with novelty and stress in free-living house sparrows

Individuals respond differently to stressors and it has been suggested that stress responses are related to coping styles (consistent individual differences in behavior and physiology). We studied behavioral responses to a novel object and corticosterone response to stress during chick rearing in free-living female house sparrows (Passer domesticus). To prevent mates from influencing each others' behavior, we removed the males temporarily from nests and tested the females the following day either with a novel object placed on the nest box or as control. The two groups differed only in behaviors that were a priori defined as responses to the novel object (latency to first feeding, time spent near the nest, and inspecting the novel object by hovering in front of it) indicating that mate-removal per se had no effect on female behavior. Based on these variables, females' coping behaviors were categorized as 'bold', 'inquisitive' or 'shy' by discriminant analysis. Baseline corticosterone, measured on the day following the novel-object or control test, was not related to any measure of coping. Stress-induced corticosterone, however, was negatively related to number of hoverings in front of the nest (a measure of explorativeness) and accordingly differed between the behavioral coping categories, with 'inquisitive' birds having the lowest stress response. We propose that the relationship between physiological stress response and behavioral response to novelty (a component of personality or coping style) may be more complex than previously suggested, and individuals cannot always be unambiguously categorized along a single personality axis.

Individual differences in the behavioural responses of meadow voles to an unfamiliar environment are not correlated with variation in resting metabolic rate

Resting metabolic rate (RMR) is highly variable between individuals within a single species and the relationship between body mass and RMR does not wholly explain this variability. One factor that could account for a portion of the residual variation is animal personality or consistent individual differences (CIDs) in behaviour, but no study has examined this relationship in a free-living population of mammals. In this paper, we test for a relationship between RMR and CIDs in activity in live-trapped meadow voles Microtus pennsylvanicus after controlling for the effect of body mass. We quantified the activity levels of voles both in an unfamiliar environment and for the first 2 min in the metabolic apparatus, and then measured RMR using open-flow respirometry. As expected, there was a linear relationship between RMR and body mass, and we found strong evidence for repeatable differences in activity levels between individuals. However, contrary to the hypothesis, we did not identify a significant correlation between CIDs in behaviour and RMR after controlling for body mass. Our results suggest that, at least within species, higher activity levels may not require a greater investment in energetically demanding tissues or increased capacity for processing of energy. Alternatively, if a relationship exists, our inability to detect it may reflect a weak behavioural signal in noisy RMR data that are influenced by many factors. Our results could also reflect an artefact of individual responses to stress or a sampling bias towards more exploratory individuals in animals captured by live-trapping.

What can whole genome expression data tell us about the ecology and evolution of personality?

Consistent individual differences in behaviour, aka personality, pose several evolutionary questions. For example, it is difficult to explain within-individual consistency in behaviour because behavioural plasticity is often advantageous. In addition, selection erodes heritable behavioural variation that is related to fitness, therefore we wish to know the mechanisms that can maintain between-individual variation in behaviour. In this paper, we argue that whole genome expression data can reveal new insights into the proximate mechanisms underlying personality, as well as its evolutionary consequences. After introducing the basics of whole genome expression analysis, we show how whole genome expression data can be used to understand whether behaviours in different contexts are affected by the same molecular mechanisms. We suggest strategies for using the power of genomics to understand what maintains behavioural variation, to study the evolution of behavioural correlations and to compare personality traits across diverse organisms.