Sex and the Syndrome: Individual and Population Consistency in Behaviour in Rock Pool Prawn Palaemon elegans

Animal personality has been widely documented across a range of species. The concept of personality is composed of individual behavioural consistency across time and between situations, and also behavioural trait correlations known as behavioural syndromes. Whilst many studies have now investigated the stability of individual personality traits, few have analysed the stability over time of entire behavioural syndromes. Here we present data from a behavioural study of rock pool prawns. We show that prawns are temporally consistent in a range of behaviours, including activity, exploration and boldness, and also that a behavioural syndrome is evident in this population. We find correlations between many behavioural traits (activity, boldness, shoaling and exploration). In addition, behavioural syndrome structure was consistent over time. Finally, few studies have explicitly studied the role of sex differences in personality traits, behavioural consistency and syndrome structure. We report behavioural differences between male and female prawns but no differences in patterns of consistency. Our study adds to the growing literature on animal personality, and provides evidence showing that syndromes themselves can exhibit temporal consistency.     

Boldness and Reproductive Fitness Correlates in the Eastern Mosquitofish, Gambusia holbrooki

Animals are known to exhibit 'personality'; that is, individual differences in behaviour that are consistent across time and/or situations. One axis of personality of particular importance for behavioural ecology is boldness, which can be defined as the tendency of an individual to take risks. The relationship between individual personality and fitness correlates, particularly those involved in reproduction, remains largely unexplored. In the current study, we used female Eastern mosquitofish ( Gambusia holbrooki ) to ascertain whether certain reproductive traits (e.g. stage of pregnancy, fecundity) are correlated with individual personality in two wild populations in New South Wales, Australia. To quantitatively assess this relationship, we tested individual fish for their level of boldness, as measured by their latency to exit a refuge and tendency to shoal in a novel environment. We also quantified individual differences in general activity and tendency to swim near the water surface and substratum. For both populations taken together, bolder individuals tended to be smaller, relatively less fecund (when taking body size into account), and spent more time near the water surface than near the substratum compared with timid individuals. Individual boldness was not correlated with either general activity or stage of pregnancy. To our knowledge, our study characterizes for the first time a relationship between an individual personality trait (boldness) and a reproductive fitness correlate (fecundity) in fishes.     

Shelter Availability,Occupancy, and Residency in Size‐Asymmetric Contests Between Rusty Crayfish,Orconectes rusticus

Contest outcomes are usually determined by differences in resource‐holding potential, the social histories of the combatants, and perceptions of resource value. One aspect of gaining an advantage is the residency effect. Prior occupancy of a particular place can affect the knowledge and motivation of the resident. There could be a tactical advantage in knowing the terrain or an increased willingness to fight to maintain control of a familiar area. In this study, we evaluated the importance of shelter residency effects relative to size differences between rusty crayfish (Orconectes rusticus) as potential competitors for access to shelter. The intensity of any residency effects was manipulated by altering the number of shelters in the arena. Our results suggest that any residency effect is very weak in this system, and if present, may often be masked by the strong and pervasive influence on contest outcome of the relative body sizes of the contestants. We also found that both shelter number and crayfish size asymmetries had strong, independent effects on levels of aggression. Dominance, but not residency status, was a factor in shelter use.     

Stability in Activity and Boldness Across Time and Context in Captive Siberian Dwarf Hamsters

Individual personality is an important source of variation in animal behavior. However, few studies have examined the reliability of individual behaviors across both time and context for even common temperament traits such as boldness, especially in mammals. We tested a laboratory colony of Siberian dwarf hamsters (Phodopus sungorus) in two similar assays, a tunnel maze and an open field, both provisioned with a home nestbox for shelter. Animals were tested in each assay at three ages, beginning at weaning. Principal components analysis on each assay identified an axis of activity level in both tests, boldness and reactivity in the tunnel maze, and nestbox orientation in the open field. All traits were moderately (7–18%) heritable. Individual activity level was the most reliably consistent trait, both within and between tests. Tunnel maze boldness, tunnel maze reactivity, and open field nestbox orientation did not correlate at any age. Correlation between boldness and activity changes from positive to negative as animals age, while reactivity was consistently negatively associated with activity. A negative correlation emerged in adults between open field activity and nestbox orientation. These results suggest that either development or habituation results in different personality trait associations in an individual over time. Individual temperament traits such as general activity level may be quite stable, but caution should be used in generalizing single assays to represent boldness across time and across contexts.     

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.     

Correlation between boldness and body mass in natural populations of the poeciliid Brachyrhaphis episcopi

The boldness of individual Brachyrhaphis episcopi , collected from regions of high and low predation, was investigated using two independent assays: (1) the time to emerge from cover and (2) the propensity to leave shoal mates and investigate a novel object. A strong correlation between the two assays was revealed such that fish that emerged from shelter sooner were also more likely to approach a novel object. This is indicative of a boldness personality axis acting across both behavioural contexts. Fish from high-predation areas were bolder than those from low-predation areas and males were bolder than females. A significant correlation between body mass, standard length ( L _S) and boldness score was also found. In general, bold fish had a greater body mass at a given L _S than shy fish. These results suggest that personality traits are strongly influenced by population-specific ecological variables and may have fitness consequences in wild populations.     

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.     

Individual‐ and population‐level personalities in a floriphilic katydid

Behaviour, including personality, informs us about the response of animals towards their changing environment. Despite the widespread occurrence of florivorous insects and the important but often underrated ecological roles that they play, the study of florivore behaviour is neglected relative to that of pollinators and other herbivores. Specifically, we do not know how different personality types can develop among florivores and enable them to persist in habitats with an ephemeral and dynamic availability of food resources. To address this knowledge gap, we investigated the following questions: whether the (a) inter‐individual differences of exploration and boldness are consistent; (b) inter‐population differences of exploration and boldness are consistent; (c) exploration and boldness are correlated. We collected individuals of the polyphagous floriphilic katydid, Phaneroptera brevis from four populations from wasteland sites in Singapore and performed a personality assay conducted in an insectary to investigate the exploratory and boldness levels of the individuals and populations. The major novel finding was that the floriphilic P. brevis katydids exhibit population‐level personality types for boldness, but not for exploration. Some katydid individuals were consistently more exploratory and bolder than other individuals. However, contrary to our predictions, we did not find any evidence of behavioural syndromes in the katydid individuals, as the boldness level for individuals was not significantly correlated with exploration for individuals. This suggests that an individual which is more exploratory may not be equally keen to take risks and consume novel food that it encounters. Our findings also suggest that boldness and exploration are linked to ecologically important behaviours, but more studies are needed to better understand population‐level personality and how and why natural selection may favour the evolution of personality in certain populations.     

Behavioural syndrome in a solitary predator is independent of body size and growth rate

Models explaining behavioural syndromes often focus on state-dependency, linking behavioural variation to individual differences in other phenotypic features. Empirical studies are, however, rare. Here, we tested for a size and growth-dependent stable behavioural syndrome in the juvenile-stages of a solitary apex predator (pike, Esox lucius), shown as repeatable foraging behaviour across risk. Pike swimming activity, latency to prey attack, number of successful and unsuccessful prey attacks was measured during the presence/absence of visual contact with a competitor or predator. Foraging behaviour across risks was considered an appropriate indicator of boldness in this solitary predator where a trade-off between foraging behaviour and threat avoidance has been reported. Support was found for a behavioural syndrome, where the rank order differences in the foraging behaviour between individuals were maintained across time and risk situation. However, individual behaviour was independent of body size and growth in conditions of high food availability, showing no evidence to support the state-dependent personality hypothesis. The importance of a combination of spatial and temporal environmental variation for generating growth differences is highlighted.     

Absence of a Context‐General Behavioural Syndrome in a Solitary Predator

The correlation of seemingly unrelated behaviours into behavioural syndromes has been established in a wide range of species and taxa. However, most studies report on short‐term behavioural correlations without insight into individual consistency or temporal stability of the behavioural syndrome. Here, we examine the individual repeatability of single behaviours, and the presence and temporal stability of a context‐general behavioural syndrome in a solitary piscivorous predator, the pike (Esox lucius). Behavioural measurements on the same individuals were quantified independently through time and across three contexts: activity in the presence of a competitor, exploration of a novel environment and boldness under predation risk. There was no indication of a temporally stable behavioural syndrome, consisting of boldness, activity and exploration, nor were individuals consistent in the separate behaviours, contradicting the general assertion of its taxonomic prevalence. Furthermore, the study did not provide support for size or growth‐dependent behaviour in this size‐dimorphic species in conditions of limited food availability. The study highlights the importance of independent multiple observations of individual behaviour across time or contexts when measuring behavioural repeatability and covariation.     

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.     

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 personality differences in Port Jackson sharks Heterodontus portusjacksoni

This study examined interindividual personality differences between Port Jackson sharks Heterodontus portusjacksoni utilizing a standard boldness assay. Additionally, the correlation between differences in individual boldness and stress reactivity was examined, exploring indications of individual coping styles. Heterodontus portusjacksoni demonstrated highly repeatable individual differences in boldness and stress reactivity. Individual boldness scores were highly repeatable across four trials such that individuals that were the fastest to emerge in the first trial were also the fastest to emerge in subsequent trials. Additionally, individuals that were the most reactive to a handling stressor in the first trial were also the most reactive in a second trial. The strong link between boldness and stress response commonly found in teleosts was also evident in this study, providing evidence of proactive‐reactive coping styles in H. portusjacksoni. These results demonstrate the presence of individual personality differences in sharks for the first time. Understanding how personality influences variation in elasmobranch behaviour such as prey choice, habitat use and activity levels is critical to better managing these top predators which play important ecological roles in marine ecosystems.     

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.     

Examining the link between personality and laterality in a feral guppy Poecilia reticulata population

This study examined whether variation in the strength and direction of lateralization in a detour task was linked with variation in three common personality measurements: boldness, activity and sociability, in a population of wild guppies Poecilia reticulata. Additionally, the aim was to determine whether any consistent correlations between these behavioural traits, known as behavioural syndromes, were present in the study population. The results revealed that all three personality traits were highly repeatable over time in both sexes. Evidence of a complex syndrome in the form of a correlation between boldness, sociability and activity was found; however, this relationship was only present in males. Males that were more active in a familiar environment emerged more quickly from shelter into a novel environment and were more social. In general, male P. reticulata were bold, active and antisocial compared to females, with these differences probably a reflection of opposing life‐history strategies. Only a weak link between the strength of cerebral lateralisation and personality was discovered and this was mediated by sex.     

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.     

Small within-day increases in temperature affects boldness and alters personality in coral reef fish

Consistent individual differences in behaviour, termed personality, are common in animal populations and can constrain their responses to ecological and environmental variation, such as temperature. Here, we show for the first time that normal within-daytime fluctuations in temperature of less than 3°C have large effects on personality for two species of juvenile coral reef fish in both observational and manipulative experiments. On average, individual scores on three personality traits (PTs), activity, boldness and aggressiveness, increased from 2.5- to sixfold as a function of temperature. However, whereas most individuals became more active, aggressive and bold across temperature contexts (were plastic), others did not; this changed the individual rank order across temperatures and thus altered personality. In addition, correlations between PTs were consistent across temperature contexts, e.g. fish that were active at a given temperature also tended to be both bold and aggressive. These results (i) highlight the importance of very carefully controlling for temperature when studying behavioural variation among and within individuals and (ii) suggest that individual differences in energy metabolism may contribute to animal personality, given that temperature has large direct effects on metabolic rates in ectotherms.     

Blood cortisol concentrations predict boldness in juvenile mulloway (Argyosomus japonicus)

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

On the Validity of a Single (Boldness) Assay in Personality Research

A common method to assess behavioral types in personality research involves the use of a single emergence test (employed by researchers working on fish, avian, mammal, amphibian, and invertebrate taxa), whereby a shorter latency to emerge from a holding container into a novel environment is inferred to represent greater ‘boldness’. Although any behavior might be context specific, studies using this single assay type must assume it reflects boldness in other similar contexts, otherwise it cannot reflect personality (defined as consistency across time and/or contexts). We attempted to validate whether a single assay of this type is correlated with other similar assays of boldness under more familiar, and less stressful, situations. We compared single emergence test scores of two species of damselfish (Pomacentrus wardi; P. amboinensis) in a novel environment, with two different behavioral assays of the same fish in subsequent repeated trials in home tanks. Although behavior was highly repeatable in home tanks, we found no correlation between emergence test scores in the novel environment and measures of latency to emerge from shelter following disturbance, or activity levels, on the first, second, or third observations in home tanks; there was also no correlation when we used average home tank scores from mixed models that accounted for individual differences (i.e., plasticity) in the rate of habituation (latency) and acclimation (activity). Our results therefore lead us to question the validity of using this single emergence test assay as a predictor of general boldness and to question the use of any single assay of behavior in personality research.     

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.