How within-group behavioural variation and task efficiency enhance fitness in a social group

How task specialization, individual task performance and within-group behavioural variation affects fitness is a longstanding and unresolved problem in our understanding of animal societies. In the temperate social spider, Anelosimus studiosus, colony members exhibit a behavioural polymorphism; females either exhibit an aggressive 'asocial' or docile 'social' phenotype. We assessed individual prey-capture success for both phenotypes, and the role of phenotypic composition on group-level prey-capture success for three prey size classes. We then estimated the effect of group phenotypic composition on fitness in a common garden, as inferred from individual egg-case masses. On average, asocial females were more successful than social females at capturing large prey, and colony-level prey-capture success was positively associated with the frequency of the asocial phenotype. Asocial colony members were also more likely to engage in prey-capture behaviour in group-foraging situations. Interestingly, our fitness estimates indicate females of both phenotypes experience increased fitness when occupying colonies containing unlike individuals. These results imply a reciprocal fitness benefit of within-colony behavioural variation, and perhaps division of labour in a spider society.     

Behavioural Syndromes in Urban and Rural Populations of Song Sparrows

Animals in urban habitats are often noticeably bold in the presence of humans. Such boldness may arise due to habituation, as urban animals learn, through repeated exposure, that passing humans do not represent a threat. However, there is growing research suggesting that: (1) inherent traits, as opposed to learned behaviour, influence which species invade urban habitats, and (2) individuals exhibit individual personality traits that limit behavioural flexibility, with the possible result that not all individuals would be able to demonstrate an appropriate level of boldness in urban environments. As a result, perhaps only birds with inherently bold personalities could successfully settle in an area of high human disturbance, and further, we might also expect to see the existence of behavioural syndromes, where boldness is correlated with variation in other behavioural traits such as aggression. In this study, we examined boldness and territorial aggression in urban and rural populations of song sparrows. We found that urban birds were bolder towards humans and that urban birds also showed higher levels of territorial aggression. We also found an overall correlation between boldness and territorial aggression, suggesting that urban boldness may be part of a behavioural syndrome. However, we see no correlation between boldness and aggression in the urban population, and thus, more work is needed to determine the mechanisms accounting for high levels of boldness and aggression urban song sparrows.     

Task specialization in two social spiders,Stegodyphus sarasinorum (Eresidae) and Anelosimus eximius (Theridiidae)

Understanding the social organization of group‐living organisms is crucial for the comprehension of the underlying selective mechanisms involved in the evolution of cooperation. Division of labour and caste formation is restricted to eusocial organisms, but behavioural asymmetries and reproductive skew is common in other group‐living animals. Permanently, social spiders form highly related groups with reproductive skew and communal brood care. We investigated task differentiation in nonreproductive tasks in two permanently and independently derived social spider species asking the following questions: Do individual spiders vary consistently in their propensity to engage in prey attack? Are individual spiders' propensities to engage in web maintenance behaviour influenced by their previous engagement in prey attack? Interestingly, we found that both species showed some degree of task specialization, but in distinctly different ways: Stegodyphus sarasinorum showed behavioural asymmetries at the individual level, that is, individual spiders that had attacked prey once were more likely to attack prey again, independent of their body size or hunger level. In contrast, Anelosimus eximius showed no individual specialization, but showed differentiation according to instar, where adult and subadult females were more likely to engage in prey attack than were juveniles. We found no evidence for division of labour between prey attack and web maintenance. Different solutions to achieve task differentiation in prey attack for the two species studied here suggest an adaptive value of task specialization in foraging for social spiders.     

Persistent social interactions beget more pronounced personalities in a desert-dwelling social spider

The social niche specialization hypothesis predicts that repeated social interactions will generate social niches within groups, thereby promoting consistent individual differences in behaviour. Current support for this hypothesis is mixed, probably because the importance of social niches is dependent upon the ecology of the species. We test whether repeated interactions among group mates generate consistent individual differences in boldness in the social spider, Stegodyphus dumicola. In support of the social niche specialization hypothesis, we found that consistent individual differences in boldness increased with longer group tenure. Interestingly, these differences took longer to appear than in previous work suggesting this species needs more persistent social interactions to shape its behaviour. Recently disturbed colonies were shyer than older colonies, possibly reflecting differences in predation risk. Our study emphasizes the importance of the social environment in generating animal personalities, but also suggests that the pattern of personality development can depend on subtle differences in species'' ecologies.     

Environmental and genetic effects shape the development of personality traits in the mangrove killifish Kryptolebias marmoratus

Consistent individual differences in behaviour are well documented, for example, individuals can be defined as consistently bold or consistently shy. To date our understanding of the mechanisms underpinning consistent individual differences in behaviour (also termed behavioural types (BTs)) remains limited. Theoretical work suggests life‐history tradeoffs drive BT variation, however, empirical support is scarce. Moreover, whilst life‐history is known to be phenotypically plastic in response to environmental conditions during ontogeny, the extent to which such plasticity drives plasticity in behavioural traits and personality remains poorly understood. Using a natural clonal vertebrate, Kryptolebias marmoratus, we control for genetic variation and investigate developmental plasticity in life‐history and three commonly studied behavioural traits (exploration, boldness, aggression) in response to three ecologically relevant environments; conspecific presence, low food and perceived risk. Simulated predation risk was the only treatment that generated repeatable behaviour i.e. personality during ontogeny. Treatments differed in their effects on mean life‐history and behavioural scores. Specifically, low food fish exhibited reduced growth rate and exploration but did not differ from control fish in their boldness or aggression scores. Conspecific presence resulted in a strong negative effect on mean aggression, boldness and exploration during ontogeny but had minimal effect on life‐history traits. Simulated predation risk resulted in increased reproductive output but had minimal effect upon average behavioural scores. Together these results suggest that life‐history plasticity/variation may be insufficient in driving variation in personality during development. Finally, using offspring derived from each rearing environment we investigate maternal effects and find strong maternal influence upon offspring size, but not behaviour. These results highlight and support the current understanding that risk perception is important in shaping personality, and that social experience during ontogeny is a major influence upon behavioural expression.     

The legacy effects of keystone individuals on collective behaviour scale to how long they remain within a group

The collective behaviour of social groups is often strongly influenced by one or few individuals, termed here ‘keystone individuals’. We examined whether the influence of keystone individuals on collective behaviour lingers after their departure and whether these lingering effects scale with their tenure in the group. In the social spider, Stegodyphus dumicola, colonies'' boldest individuals wield a disproportionately large influence over colony behaviour. We experimentally manipulated keystones'' tenure in laboratory-housed colonies and tracked their legacy effects on collective prey capture following their removal. We found that bolder keystones caused more aggressive collective foraging behaviour and catalysed greater inter-individual variation in boldness within their colonies. The longer keystones remained in a colony, the longer both of these effects lingered after their departure. Our data demonstrate that, long after their disappearance, keystones have large and lasting effects on social dynamics at both the individual and colony levels.     

Personality composition is more important than group size in determining collective foraging behaviour in the wild

Describing the factors that shape collective behaviour is central to our understanding of animal societies. Countless studies have demonstrated an effect of group size in the emergence of collective behaviours, but comparatively few have accounted for the composition/diversity of behavioural phenotypes, which is often conflated with group size. Here, we simultaneously examine the effect of personality composition and group size on nest architecture and collective foraging aggressiveness in the social spider Stegodyphus dumicola. We created colonies of two different sizes (10 or 30 individuals) and four compositions of boldness (all bold, all shy, mixed bold and shy, or average individuals) in the field and then measured their collective behaviour. Larger colonies produced bigger capture webs, while colonies containing a higher proportion of bold individuals responded to and attacked prey more rapidly. The number of attackers during collective foraging was determined jointly by composition and size, although composition had an effect size more than twice that of colony size: our results suggest that colonies of just 10 bold spiders would attack prey with as many attackers as colonies of 110 ‘average’ spiders. Thus, personality composition is a more potent (albeit more cryptic) determinant of collective foraging in these societies.     

Behavioural and physiological correlates of personality in greylag geese (Anser anser)

Personality means suites of correlated behavioural traits, also referred to as “behavioural syndromes” or “personality dimensions”. Across animal taxa similar combinations of traits seem to prevail, which may have proximate foundation in common neuroendocrine mechanisms. Hitherto, these have been rarely studied in intact social settings. We investigated personalities of greylag goose males from a free-roaming flock that shows complex social relationships. In connection with our longitudinal study on the consistency of behavioural and physiological responses to multiple challenges, we asked whether and how single, personality-related behavioural traits correlate with each other to form personality dimension(s). We tested whether these dimensions were related to physiological characteristics that previously showed limited plasticity (heart rate (HR), baseline and stress-induced excreted immuno-reactive corticosterone (BM), and testosterone metabolites levels) and, furthermore, to age, body measures, and dominance rank. Principal-components analysis based on behavioural variables revealed two factors: 51.1% of variability was explained by “aggressiveness” and a further 19.1% by “sociability”. “Aggressiveness” comprised correlated measures of aggression, subordinance, boldness, vigilance, and proximity to the mate. This “aggressiveness” positively correlated with stress-induced BM levels, the HR increase during aggressive interactions, and with dominance rank, which may suggest proximate and functional contingencies of this personality dimension.     

What's your move? Movement as a link between personality and spatial dynamics in animal populations

Recent studies have established the ecological and evolutionary importance of animal personalities. Individual differences in movement and space‐use, fundamental to many personality traits (e.g. activity, boldness and exploratory behaviour) have been documented across many species and contexts, for instance personality‐dependent dispersal syndromes. Yet, insights from the concurrently developing movement ecology paradigm are rarely considered and recent evidence for other personality‐dependent movements and space‐use lack a general unifying framework. We propose a conceptual framework for personality‐dependent spatial ecology. We link expectations derived from the movement ecology paradigm with behavioural reaction‐norms to offer specific predictions on the interactions between environmental factors, such as resource distribution or landscape structure, and intrinsic behavioural variation. We consider how environmental heterogeneity and individual consistency in movements that carry‐over across spatial scales can lead to personality‐dependent: (1) foraging search performance; (2) habitat preference; (3) home range utilization patterns; (4) social network structure and (5) emergence of assortative population structure with spatial clusters of personalities. We support our conceptual model with spatially explicit simulations of behavioural variation in space‐use, demonstrating the emergence of complex population‐level patterns from differences in simple individual‐level behaviours. Consideration of consistent individual variation in space‐use will facilitate mechanistic understanding of processes that drive social, spatial, ecological and evolutionary dynamics in heterogeneous environments.     

两种生态相关猎物鱼个性的种间差异及其捕食者效应

为探究不同猎物鱼个性的种间差异及其捕食者效应, 实验以乌鳢(Channa argus)为天然的捕食者, 选取自然界通常形成混合种群的高体鳑鲏(Rhodeus ocellatus)和麦穗鱼(Pseudorasbora parva)作为猎物鱼, 设置有捕食者和无捕食者处理组开展同质园实验; 之后, 分别测定了经历捕食环境处理的两种猎物鱼的探索性、活跃性和勇敢性3类个性特征, 分析两种猎物鱼个性特征的种间差异及其环境依赖性。结果发现: (1)高体鳑鲏和麦穗鱼个性存在显著的种间差异, 不管是否经历捕食者处理, 高体鳑鲏的探索性、活跃性和勇敢性均显著强于麦穗鱼(P<0.05); (2)捕食者处理导致高体鳑鲏和麦穗鱼探索性和勇敢性有增强的趋势, 但对二者的活跃性均无显著影响(P>0.05); (3)捕食者处理弱化了高体鳑鲏和麦穗鱼不同个性特征的种间差异, 强化了各自不同个性特征的偶联。结果提示: 两种猎物鱼个性特征的种间差异显著且均具有捕食者效应, 有捕食者环境下两种猎物鱼个性特征的种间差异变小, 表现出趋同化适应的趋势。     

Sequential hermaphroditism and personality in a clonal vertebrate: the mangrove killifish

Individuals are regularly documented to consistently differ in their behavioural types (BTs). For example, some individuals are bold whereas others are shy. Within the human personality literature, the big five personality dimensions are commonly documented to be sex-specific with testosterone suggested to underpin traits such as aggressiveness. In non-human animals recent research suggests sex-specific BT expression may be influenced by ecology, mating system and sexual selection. While most research on sex-specific personality has focused on dioecious species, we explore sex differences in BT expression in a sequential hermaphrodite the mangrove killifish. We replicate within 7 isogenic genotypes and investigate sex differences (hermaphrodite and secondary male) in three BTs (exploration, boldness and aggression). This approach allows us to investigate sex differences in BT expression whilst controlling for genetic variation. In this study we find that both secondary males and hermaphrodites are repeatable at the individual level yet there was no difference between the sexes in average BT scores. Furthermore, aggression scores differed between genotypes, and were repeatable at the genotype level, suggesting strong genetic control. Finally, male boldness was significantly more repeatable than hermaphrodites potentially supporting recent proposals relating to sexual selection. We document a behavioural syndrome in male fish with bolder individuals being more aggressive, this behavioural syndrome was not observed however in hermaphrodites. In contrast to a previous developmental study in this species exploration did not correlate with either aggression or boldness in either males or hermaphrodites.     

A multi-trait,field-based examination of personality in a semi-aquatic turtle

Studies documenting and quantifying personality traits are common in animal behavior. Such studies often consider the nature of individual variation and personality as correlated with a variety of natural history, physiological, or ecological traits, and therefore consider the importance of personality for strategies in wild systems. Though such studies have contributed markedly to our understanding of the important aspects of personality that may covary with a variety of factors that might affect fitness, much of the research on animal personalities is taxonomically limited. To supplement and compliment the laboratory study of reptile personality, we examined the patterns of multiple personality traits in wild Eastern painted turtles (Chrysemys picta) in the field. We examined patterns of aggression, sociability, and boldness across these traits in different contexts in 103 adult, wild-caught turtles. We found strong correlations both within and among the focal behavioral axes, representing robust evidence for personality in this species. Specifically, we found strong relationships among many measures of aggression, as well as relationships between aggression and our measures of boldness. Finally, we note a tendency for sociability in our turtles, with animals scoring high on sociability showing lower tendency toward aggression. Overall, our study provides robust evidence for correlated suites of behavioral traits, or personality, in a semi-aquatic turtle surveyed in the wild. Future work should continue to expand the range of traits examined to more fully consider the ecological consequences of variation in personality in this and similar species.     

Social status and personality: stability in social state can promote consistency of behavioural responses

Stability of ‘state’ has been suggested as an underlying factor explaining behavioural stability and animal personality (i.e. variation among, and consistency within individuals in behavioural responses), but the possibility that stable social relationships represent such states remains unexplored. Here, we investigated the influence of social status on the expression and consistency of behaviours by experimentally changing social status between repeated personality assays. We used male domestic fowl (Gallus gallus domesticus), a social species that forms relatively stable dominance hierarchies, and showed that behavioural responses were strongly affected by social status, but also by individual characteristics. The level of vigilance, activity and exploration changed with social status, whereas boldness appeared as a stable individual property, independent of status. Furthermore, variation in vocalization predicted future social status, indicating that individual behaviours can both be a predictor and a consequence of social status, depending on the aspect in focus. Our results illustrate that social states contribute to both variation and stability in behavioural responses, and should therefore be taken into account when investigating and interpreting variation in personality.     

LETTERS

We used video recordings to perform a behavioural analysis of a Village Weaver Ploceus cucullatus colony in Awash National Park, Ethiopia. We focused specifically on female behaviour during the pair-formation, egg-laying and early-incubation phases of the nesting cycle. A factor analysis revealed that females’ temporal investments can be partitioned into three broad behavioural categories: (1) behaviours associated with aggression, (2) time away/ inside nest, and (3) behaviours associated with copulation. Time budgets revealed females spent approximately 61% of their time away from the colony and 38% of their time inside their nests. The performance of individual behaviours was largely a function of temporal and social factors, including when the birds were observed and the personality of the territorial male. Females invested more time away from the nest earlier and more time inside the nest later in the observation period. One aspect of a territorial male’s personality, boldness, was a predictor of several female behaviours: a female Village Weaver was significantly more likely to remain on a territory if the resident male had a tendency not to flee during colony-wide disturbances. Lastly, a path analysis revealed that females exhibited consistent sequential patterns of behaviour.     

Sex-Specific Aggression and Antipredator Behaviour in Young Brown Trout

Sex differences in adult behaviour are often interpreted as consequences of sexual selection and/or different reproductive roles in males and females. Sex-specific juvenile behaviour, however, has received less attention. Adult brown trout males are more aggressive than females during spawning and juvenile aggression may be genetically correlated with adult aggression in fish. We therefore tested the prediction that immature brown trout males are more aggressive and bolder than immature females. Because previous work has suggested that precocious maturation increases dominance in salmonids, we included precocious males in the study to test the prediction that early sexual maturation increase male aggression and boldness. Aggression and dominance relations were estimated in dyadic contests, whereas boldness was measured as a response to simulated predation risk using a model heron. Independent of maturity state, males initiated more than twice as many agonistic interactions as females in intersexual contests. However, males were not significantly more likely to win these contests than females. The response to a first predator attack did not differ between sex categories, but males reacted less to a second predator attack than females. Sexual maturity did not affect the antipredator response in males. Since there is no evidence from field studies that stream-living immature male and female salmonids differ in growth rate, it appears unlikely that the sex differences demonstrated are behavioural consequences of sex-specific investment in growth. It seems more likely that sex-specific behaviour arises as a correlated response to sexually selected gene actions promoting differential behaviour in adult males and females during reproduction. Alternatively, sex differences may develop gradually during juvenile life, because a gradual developmental program should be less costly than a sudden behavioural change at the onset of sexual maturity.     

Boldness as a consistent personality trait in the noble crayfish, <Emphasis Type="Italic">Astacus astacus</Emphasis>

Consistent individual differences in behavioural responses to perceived predation risk may have extensive ecological and evolutionary implications. We studied the repeatability of boldness across time and its relation to resource holding potential in the noble crayfish, Astacus astacus L., using predator-naïve immature individuals. We followed individual’s shelter use both with and without exposure to the chemical and physical cues of predators, and with and without the presence of a conspecific. In addition, we examined if armament, i.e. relative chelae size, would be correlated with individual differences in behaviour. Individuals showed repeatable behaviours across time and context. Individuals that occupied the shelter in competitive dyadic tests also spent more time in the shelter during individual control observations, suggesting that boldness is a personality trait that does not necessarily relate positively to high resource holding potential in the noble crayfish. The relative size of chelae did not correlate with any of the measured behavioural variables. Our results suggest that boldness can be considered as individually consistent and ecologically important personality trait in the noble crayfish.     

Comparison of personality between juveniles and adults in clonal gecko species

The developmental perspectives of animal personality enhance our understanding of how personality structure changes in relation to life stage. Clonal animals are ideal models for developmental studies because personality differences can be solely attributed to environmental factors. Here, I investigated the presence of personality within a species of clonal gecko, Lepidodactylus lugubris, at different developmental stages. For juveniles and adult geckos, I measured exploration (reaction to a novel situation) and boldness (risk-prone tendency) and evaluated repeatability and correlation of these behavioural traits. Each gecko exhibited different exploration and boldness with significant repeatability through time but no correlation between these behavioural traits. Small juveniles were composed of only bold and low explorative individuals but large juveniles and adults were composed of various personality type individuals. These results demonstrate that subject geckos have a similar personality structure across life stages and that exploration and boldness are independent personality without forming behavioural syndrome structure. Biased composition of personality type between life stages suggests that appearance of different personality type individuals during an early ontogenetic stage generates personality variation within the clonal population. This study provides developmental insight about personality structure and its composition in clonal animals living in the wild.     

Consistent behavioural traits and behavioural syndromes in pairs of the false clown anemonefish Amphiprion ocellaris

Using the social clown anemonefish Amphiprion ocellaris, whether individuals exhibited consistency in activity levels, boldness and sociability in a paired context, and whether these three behavioural traits were positively correlated within a single behavioural syndrome, was investigated. The results highlight that consistent individual differences in behaviour are expressed in a social fish and suggest that consistent behavioural traits and behavioural syndromes could influence the structure and functioning of their societies.     

Exposure to predation generates personality in threespined sticklebacks (Gasterosteus aculeatus)

A perplexing new question that has emerged from the recent surge of interest in behavioural syndromes or animal personalities is – why do individual animals behave consistently when behavioural flexibility is advantageous? If individuals have a tendency to be generally aggressive, then a relatively aggressive individual might be overly aggressive towards offspring, mates or even predators. Despite these costs, studies in several taxa have shown that individuals that are more aggressive are also relatively bold. However, the behavioural correlation is not universal; even within a species, population comparisons have shown that boldness and aggressiveness are correlated in populations of sticklebacks that are under strong predation pressure, but not in low predation populations. Here, we provide the first demonstration that an environmental factor can induce a correlation between boldness and aggressiveness. Boldness under predation risk and aggressiveness towards a conspecific were measured before and after sticklebacks were exposed to predation by trout, which predated half the sticklebacks. Exposure to predation generated the boldness–aggressiveness behavioural correlation. The behavioural correlation was produced by both selection by predators and behavioural plasticity. These results support the hypothesis that certain correlations between behaviours might be adaptive in some environments.     

Differences in aggression,activity and boldness between native and introduced populations of an invasive crayfish

Aggressiveness, along with foraging voracity and boldness, are key behavioral mechanisms underlying the competitive displacement and invasion success of exotic species. However, do aggressiveness, voracity and boldness of the invader depend on the presence of an ecologically similar native competitor in the invaded community? We conducted four behavioral assays to compare aggression, foraging voracity, threat response and boldness to forage under predation risk of multiple populations of exotic signal crayfish Pacifastacus leniusculus across its native and invaded range with and without a native congener, the Shasta crayfish P. fortis. We predicted that signal crayfish from the invaded range and sympatric with a native congener (IRS) should be more aggressive to outcompete a close competitor than populations from the native range (NR) or invaded range and allopatric to a native congener (IRA). Furthermore, we predicted that IRS populations of signal crayfish should be more voracious, but less bold to forage under predation risk since native predators and prey likely possess appropriate behavioral responses to the invader. Contrary to our predictions, results indicated that IRA signal crayfish were more aggressive towards conspecifics and more voracious and active foragers, yet also bolder to forage under predation risk in comparison to NR and IRS populations, which did not differ in behavior. Higher aggression/voracity/boldness was positively correlated with prey consumption rates, and hence potential impacts on prey. We suggest that the positive correlations between aggression/voracity/boldness are the result of an overall aggression syndrome. Results of stream surveys indicated that IRA streams have significantly lower prey biomass than in IRS streams, which may drive invading signal crayfish to be more aggressive/voracious/bold to acquire resources to establish a population.