Adaptive strategies for managing uncertainty may explain personality‐related differences in behavioural plasticity

There is growing evidence that individuals within populations show consistent differences in their behaviour across contexts (personality), and that personality is associated with the extent to which individuals adjust their behaviour as function of changing conditions (behavioural plasticity). We propose an evolutionary explanation for a link between personality and plasticity based upon how individuals manage uncertainty. Individuals can employ three categories of tactics to manage uncertainty. They can 1) gather information (sample) to reduce uncertainty, 2) show strategic (state‐dependent) preferences for options that differ in their associated variances in rewards (i.e. variance‐sensitivity), or 3) invest in insurance to mitigate the consequences of uncertainty. We explicitly outline how individual differences in the use of any of these tactics can generate personality‐related differences in behavioural plasticity. For example, sampling effort is likely to co‐vary with individual activity and exploration behaviours, while simultaneously creating population variation in reactions to changes in environmental conditions. Individual differences in the use of insurance may be associated with differences in risk‐taking behaviours, such as boldness in the face of predation, thereby influencing the degree of adaptive plasticity across individuals. Population variation in responsiveness to environmental changes may also reflect individual differences in variance‐sensitivity, because stochastic change in the environment increases variances in rewards, which may both attract and benefit variance‐prone individuals, but not variance‐averse individuals. We review the existing evidence that individual variation in strategies for managing uncertainty exist, and describe how positive‐feedbacks between sampling, variance‐sensitivity and insurance can maintain and exaggerate even small initial differences between individuals in the relative use of these tactics. Given the pervasiveness of the problem of uncertainty, alternative strategies for managing uncertainty may provide a powerful explanation for consistent differences in behaviour and behavioural plasticity for a wide range of traits.     

Additive and nonadditive genetic variation in avian personality traits

Individuals of all vertebrate species differ consistently in their reactions to mildly stressful challenges. These typical reactions, described as personalities or coping strategies, have a clear genetic basis, but the structure of their inheritance in natural populations is almost unknown. We carried out a quantitative genetic analysis of two personality traits (exploration and boldness) and the combination of these two traits (early exploratory behaviour). This study was carried out on the lines resulting from a two-directional artificial selection experiment on early exploratory behaviour (EEB) of great tits (Parus major) originating from a wild population. In analyses using the original lines, reciprocal F(1) and reciprocal first backcross generations, additive, dominance, maternal effects ands sex-dependent expression of exploration, boldness and EEB were estimated. Both additive and dominant genetic effects were important determinants of phenotypic variation in exploratory behaviour and boldness. However, no sex-dependent expression was observed in either of these personality traits. These results are discussed with respect to the maintenance of genetic variation in personality traits, and the expected genetic structure of other behavioural and life history traits in general.     

Does individual personality predict male mating preference for female body size in the Trinidadian guppy?

Within populations, individual animals vary considerably in their behaviour, including mate choice and personality. There is mounting interest in the potential covariation between these two behaviours within individuals, such that personality would influence mate choice. We experimentally tested this proposition under controlled laboratory conditions using male Trinidadian guppies (Poecilia reticulata) as a model study system. We assayed repeatedly the mating preference of individual males for females based on their body size. Additionally, we assayed repeatedly two ecologically relevant personality traits in males, namely exploration of a novel environment and boldness under a simulated predation threat. Finally, we analysed whether male mating preference and personality traits were repeatable, and tested whether the personality of individual males was correlated (covaried) with their mating preference scores. Although all but one of the measures of exploration and boldness behaviour were repeatable over time, male mating preference scores were not repeatable. Measures of male exploration and boldness were not inter-correlated among individuals, suggesting the absence of a behavioural syndrome between exploration and boldness. Unexpectedly, males did not exhibit on average a significant mating preference for larger females over smaller ones; they chose randomly between the paired stimulus females. Overall, we found no compelling evidence for a relationship between individual personality traits and mating preference in male guppies, suggesting that personality does not predict mate choice, at least in our study population and under our experimental conditions. We discuss potential factors, other than male personality and body length, that might maintain inter-individual variation in male mating preferences in the guppy in the wild.     

Heritability and social brood effects on personality in juvenile and adult life‐history stages in a wild passerine

How has evolution led to the variation in behavioural phenotypes (personalities) in a population? Knowledge of whether personality is heritable, and to what degree it is influenced by the social environment, is crucial to understanding its evolutionary significance, yet few estimates are available from natural populations. We tracked three behavioural traits during different life‐history stages in a pedigreed population of wild house sparrows. Using a quantitative genetic approach, we demonstrated heritability in adult exploration, and in nestling activity after accounting for fixed effects, but not in adult boldness. We did not detect maternal effects on any traits, but we did detect a social brood effect on nestling activity. Boldness, exploration and nestling activity in this population did not form a behavioural syndrome, suggesting that selection could act independently on these behavioural traits in this species, although we found no consistent support for phenotypic selection on these traits. Our work shows that repeatable behaviours can vary in their heritability and that social context influences personality traits. Future efforts could separate whether personality traits differ in heritability because they have served specific functional roles in the evolution of the phenotype or because our concept of personality and the stability of behaviour needs to be revised.     

Evolutionary Perspective on the Interplay Between Family Life,and Parent and Offspring Personality

Consistent inter‐individual variation in behaviour over time and across contexts has been reported for a wide variety of animals, a phenomenon commonly referred to as personality. As behavioural patterns develop inside families, rearing conditions could have lasting effects on the expression of adult personality. In species with parental care, conflicts among family members impose selection on parental and offspring behaviour through coadaptation. Here, we argue that the interplay between the evolution of personality traits (i.e. boldness, exploration, activity, aggressiveness and sociability) expressed outside the family context and the specialized behaviours expressed inside families (i.e. offspring begging behaviour and parental response to offspring solicitations) can have important evolutionary consequences. Personality differences between parents may relate to the typically observed variation in the way they respond to offspring demand, and dependent offspring may already express personality differences, which may relate to the way they communicate with their parents and siblings. However, there has been little research on how personality relates to parental and offspring behaviours. Future research should thus focus on how and why personality may be related to the specialized parent and offspring behaviour that evolved as adaptations to family life.     

Personality and urbanization: behavioural traits and <Emphasis Type="Italic">DRD4</Emphasis> SNP830 polymorphisms in great tits in Barcelona city

Most examples of adaptation to the urban environment relate to plasticity processes rather than to natural selection. Personality, however, defined as consistent individual differences in behaviour related to exploration, caution, and neophobia, is a good behavioural candidate character to study natural selection in relation to the urban habitat due to its heritable variation. The aim of this paper was to analyse variation in personality by comparing urban and forest great tits Parus major using standard tests of exploratory behaviour and boldness. We studied personality in 130 wild great tits captured in Barcelona city and nearby forests and found that urban birds were more explorative and bolder towards a novel object than forest birds. Genotype frequencies of the DRD4 SNP830 polymorphism, a gene region often associated with personality variation, varied significantly between forest and urban birds. Behavioural scores, however, were not correlated with this polymorphism in our population. Exploration scores correlated to boldness for forest birds but not for urban birds. Our findings suggest that the novel selection pressures of the urban environment favour the decoupling of behavioural traits that commonly form behavioural syndromes in the wild.     

Match–Mismatch Experiments Using Photoperiod Expose Developmental Plasticity of Personality Traits

Behavioural differences between individuals are often found to be consistent across contexts and/or over time, although recent studies suggest that ontogenetic processes and learning might influence personality. During ontogeny, environmental influences may play an important role in shaping an individual's personality as well as its physiology. Seasonal changes are ubiquitous and known to influence development. To study developmental plasticity, of behaviour and physiology in the wild cavy (Cavia aperea), we manipulated the photoperiod in a fully crossed match–mismatch design by simulating spring and autumn photoperiod until weaning and subsequently moving half of the animals into the mismatching photoperiod. We found developmental plasticity in behavioural and physiological traits before and after sexual maturation for growth, resting metabolic rate and fearlessness. For fearlessness, changes in response to the opposite photoperiod were more pronounced in males than in females. Exploration and boldness were only influenced by early, but not by late photoperiod. No sex differences were found for these two traits. Even though our treatment changed average trait expression, some behavioural traits proved consistent over time, but physiological traits were not. Fearlessness was consistent only in animals that did not change photoperiod during development, whereas exploration and boldness were consistent over time regardless of photoperiodic treatment. Our study shows that in response to a change in photoperiod personality traits differ substantially in developmental plasticity.     

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.     

Individual variation in behavioural plasticity: direct and indirect effects of boldness,exploration and sociability on habituation to predators in lizards

Little is known about the factors causing variation in behavioural plasticity and the interplay between personality and plasticity. Habituation to predators is a special case of behavioural plasticity. We investigated the direct and indirect effects of boldness, exploration and sociability traits on the habituation ability of Iberian wall lizards, considering exposure and sex effects. Individual boldness was consistent across several non-habituation contexts, but it did not significantly affect habituation. Exploration had a strong direct effect on habituation, with more exploratory individuals being able to habituate faster than less exploratory ones, probably because of their ability to assess risk better. Individual variation in habituation was also affected by sociability, but this was an indirect effect mediated by exposure to the predator. Less social individuals avoided refuges with conspecific cues, increasing exposure to the predator and eventually habituation. Finally, the direct effects of sex (females habituated faster than males) were opposite to its indirect effects through exposure. We conclude that risk assessment, instead of the proactivity–reactivity gradient usually considered in the literature, can affect behavioural plasticity through complex interactions between direct and indirect effects, including exploratory behaviour, degree of exposure to the predator and sex, which represent novel mechanisms generating inter-individual variation in plasticity.     

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.     

Picking personalities apart: estimating the influence of predation,sex and body size on boldness in the guppy Poecilia reticulata

Predation is a strong selective force in most natural systems, potentially fueling evolutionary changes in prey morphology, life history and behaviour. Recent work has suggested that contrasting predation pressures may lead to population differentiation in personality traits. However, there are indications that these personality traits also differ between sexes and not necessarily in a consistent way between populations. We used an integrative approach to quantify boldness (latency to emerge from a shelter) in wild‐caught guppies in relation to predation pressure, population origin, sex and size. In addition we quantified the repeatability of these personality traits. We show that predation regime had significant effects on emergence time. In general, fish from high predation localities emerged sooner from the shelter compared to those from low predation localities. We found strong sex differences; males were significantly bolder than females. The relationship between emergence time and body size was non‐significant in all populations. We discuss what responses to expect from predator‐naïve versus predator‐experienced individuals and how this can be linked to the shyness–boldness continuum.     

Parallel and nonparallel behavioural evolution in response to parasitism and predation in Trinidadian guppies

Natural enemies such as predators and parasites are known to shape intraspecific variability of behaviour and personality in natural populations, yet several key questions remain: (i) What is the relative importance of predation vs. parasitism in shaping intraspecific variation of behaviour across generations? (ii) What are the contributions of genetic and plastic effects to this behavioural divergence? (iii) And to what extent are responses to predation and parasitism repeatable across independent evolutionary lineages? We addressed these questions using Trinidadian guppies (Poecilia reticulata) (i) varying in their exposure to dangerous fish predators and Gyrodactylus ectoparasites for (ii) both wild‐caught F0 and laboratory‐reared F2 individuals and coming from (iii) multiple independent evolutionary lineages (i.e. independent drainages). Several key findings emerged. First, a population's history of predation and parasitism influenced behavioural profiles, but to different extent depending on the behaviour considered (activity, shoaling or boldness). Second, we had evidence for some genetic effects of predation regime on behaviour, with differences in activity of F2 laboratory‐reared individuals, but not for parasitism, which had only plastic effects on the boldness of wild‐caught F0 individuals. Third, the two lineages showed a mixture of parallel and nonparallel responses to predation/parasitism, with parallel responses being stronger for predation than for parasitism and for activity and boldness than for shoaling. These findings suggest that different sets of behaviours provide different pay‐offs in alternative predation/parasitism environments and that parasitism has more transient effects in shaping intraspecific variation of behaviour than does predation.     

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.     

Personality over ontogeny in zebra finches: long-term repeatable traits but unstable behavioural syndromes

A crucial assumption of animal personality research is that behaviour is consistent over time, showing a high repeatability within individuals. This assumption is often made, sometimes tested using short time intervals between behavioural tests, but rarely thoroughly investigated across long time intervals crossing different stages of ontogeny. We performed such a longitudinal test across three life stages in zebra finches (Taeniopygia guttata), representing about 15-20% of their life span in captivity, and found repeatabilities ranging from 0.03 to 0.67. Fearlessness and exploration were the most repeatable traits both within and across life stages. Activity and aggression were repeatable across, but not or only partly within life stages. Boldness was not repeatable. Furthermore, we found no evidence for a consistent behavioural syndrome structure across ontogeny. Our results indicate that the consistency of behavioural traits and their correlations might be overestimated and suggest that life-long stability of animal personality should not simply be assumed.     

Behavioural variation in Eurasian perch populations with respect to relative catchability

Animal personalities, i.e. consistent individual differences in behaviour, are currently of high interest among behavioural and evolutionary biologists. The topic has received increasing attention also in fisheries science because selective harvesting of certain behavioural types might impose fishing-induced selection on personality. Here, we ice-fished wild Eurasian perch (Perca fluviatilis) from three native populations and investigated whether differences in relative catchability would explain behavioural differences observed in experimental conditions. We inferred relative catchability differences indirectly by fishing each location first with generally inefficient artificial bait and then by more efficient natural bait. The captured, individually tagged fish were tested in groups for their exploration tendency, activity and boldness under authentic predation risk in semi-natural stream channels. Fish that were easily captured first with artificial bait expressed fast exploration and acute activity, whereas the fish captured with natural bait showed less active and explorative behaviour. Differences in relative catchability did not explain variation in boldness or body size. In conclusion, we found that (1) Eurasian perch differing in relative catchability differ in certain behavioural traits, (2) fast explorers are more common among fish that get easily caught compared to fish that are more difficult to catch, (3) relative catchability explains more behavioural variation in a novel environment than in a familiar one and (4) selectivity of recreational angling on fish behaviour may depend on applied angling method and the effort spent on each location.     

Aggressiveness,Boldness and Parental Food Provisioning in Male House Wrens (Troglodytes aedon)

Behavioural syndromes have been identified in a large number of species, yet our understanding of them in an ecological context remains poor. Specifically, there are few data that relate behavioural syndromes to other biologically important behaviours and, ultimately, to reproductive success. In this field study, we examined the aggressiveness and boldness of free‐living male house wrens (Troglodytes aedon) and found a statistically significant positive relationship between these two behaviours (i.e. a behavioural syndrome). When we examined the two axes of this behavioural syndrome in relation to the male's share of provisioning, we found a negative relation between a male's aggressiveness and his provisioning rate, but no relationship between male boldness and provisioning behaviour. These differences in provisioning behaviour among males with different levels of aggression may reflect differences in reproductive strategies or different life‐history trade‐offs among males. Moreover, these results indicate that while some behavioural traits may be correlated, this does not mean that traits that compose the behavioural syndrome cannot evolve independently of one another.     

Size‐induced phenotypic reaction norms in a parasitoid wasp: an examination of life‐history and behavioural traits

The amount of resources available during development often affects body size, causing phenotypic variation in life‐history traits and reproductive behaviours. However, past studies have seldom examined the reaction norms of both life‐history and behavioural traits versus body size. We measured the phenotypic plasticity of several life‐history (age‐specific egg load, egg size, longevity) and behavioural (oviposition rate, host marking rate, walking speed) traits of the egg parasitoid Telenomus podisi Ashmead (Hymenoptera: Scelionidae) in response to body size variation. We predicted that life‐history traits would show more evidence of size compensation than behavioural traits, resulting in fewer positively‐sloped size versus trait reaction norms among the former. As predicted by life‐history models, smaller wasps appear to shift resource allocation towards early‐life reproduction, having a similar egg load to large individuals 9 days after emergence. Surprisingly, longevity was unaffected by body size. However, egg size, the number of offspring produced during oviposition bouts, and the rate of subsequent egg synthesis were greater for larger individuals. In addition, as predicted, the reaction norms of behavioural traits versus body size were all positively sloped. Thus, despite possible adaptive compensatory plasticity of life‐history traits by small individuals, behavioural constraints directly related to body size would contribute to maintaining a positive size–fitness relationship.     

Early environment influences later performance in fishes

Conditions fish encounter during embryogenesis and early life history can leave lasting effects not only on morphology, but also on growth rate, life‐history and behavioural traits. The ecology of offspring can be affected by conditions experienced by their parents and mother in particular. This review summarizes such early impacts and their ecological influences for a variety of teleost species, but with special reference to salmonids. Growth and adult body size, sex ratio, egg size, lifespan and tendency to migrate can all be affected by early influences. Mechanisms behind such phenotypically plastic impacts are not well known, but epigenetic change appears to be one central mechanism. The thermal regime during development and incubation is particularly important, but also early food consumption and intraspecific density can all be responsible for later life‐history variation. For behavioural traits, early experiences with effects on brain, sensory development and cognition appear essential. This may also influence boldness and other social behaviours such as mate choice. At the end of the review, several issues and questions for future studies are given.     

Does it always pay to defend one's nest? A case study in African penguin

Throughout the animal kingdom, individual variation in reproductive success is commonly observed, even under similar environmental conditions. However, the mechanisms behind such differences remain unclear. The notion of behavioural consistency in animals has developed rapidly since the early 21st century partly as an approach to understand among‐individual differences. In this context, a number of studies have highlighted the influence of pair assortment in personality on breeding success. In this study, we related breeding success to individual behaviour, specifically a risk‐taking behaviour, and pair assortment per behaviour in African penguins (Spheniscus demersus) over two breeding seasons of contrasting food availability. On Bird Island, Algoa Bay, South Africa, we used indices of boldness and overall mobility in penguins’ nest defence behaviour as a response to a standard pedestrian approach during chick‐rearing. These behaviours were consistent over the trials and indicated these traits may be related to personality in African penguins. Individuals were categorized as risk‐prone (“bold,” “mobile”) or risk‐averse (“shy,” “non‐mobile”). We then assessed their breeding success through chick growth and survival over 4 weeks in 2015 and 2016. There was weak positive assortment of pairs in relation to nest defence behaviour. However, pair assortment did not significantly influence birds’ breeding success. Shy penguins were generally the most successful (had the highest chick growth rates), which was especially apparent during a food shortage in 2016, possibly reflecting a higher energy investment when foraging. In contrast, chicks from bold parents grew significantly slower, especially in 2016. Bold parents may defend their nest successfully against predation or intra‐specific aggression when food is abundant, but when predation risks are limited and food availability is low, this strategy may not be beneficial. In the context of climate change, where food shortage events may become more frequent, risk‐averse individuals may be favoured and genetic diversity may be reduced in African penguins.     

Personality traits and behavioural profiles in the domestic canary are affected by sex and photoperiod

Personality traits and behavioural profiles are generally assumed to be stable in adulthood. Yet, it has been hypothesised that animals should cope with cyclical fluctuations by adjusting both single behaviours and suites of behaviour. Photoperiod is well known to induce hormonal and physiological changes, and these changes can in turn affect personality traits and behavioural profiles. This study is the first to explicitly investigate the influence of photoperiod on both behavioural profiles and personality traits. Six potential personality traits (within‐flock activity, ability to escape, response to threat, isolation calling, boldness and neophobia) and dominance were measured four times in 96 domestic canaries Serinus canaria (48 males and 48 females): twice during a long photoperiod (Long Days) and 6 months later twice during a short photoperiod (Short Days). Without regard to sex and photoperiod, most traits were highly repeatable, and bolder canaries were more dominant, less sensitive to an external threat and to isolation and less neophobic. In addition, the more active individuals within a flock were the more difficult to catch. Yet, both sex and photoperiod affected personality traits and behavioural profiles. Personality traits remained repeatable within each photoperiod though we observed behavioural plasticity and sex differences for response to threat, neophobia and within‐flock activity. Concerning behavioural profiles, the negative relationship between boldness and neophobia remained homogenous in both sexes during Short Days as well as during Long Days. Then, the more active individuals within a flock were the more difficult to catch in Short Days but not in Long Days. Finally, the other correlations not only varied with photoperiod but also with sex. Our study highlights the importance of photoperiod and sex in the expression of personality traits and behavioural profiles, and of the need to measure them across the whole photoperiodic cycle.