Between-individual Differences In Behaviour Research Articles

The association between personalities, alternative breeding strategies and reproductive success in dunnocks.

Although consistent between-individual differences in behaviour (i.e. animal personality) are ubiquitous in natural populations, relatively few studies have examined how personalities influence the formation of social relationships. Yet, behavioural characteristics of both sexes might be key when it comes to pair-bond formation, and cooperation with partners to successfully rear offspring. We here use a wild population of dunnocks (Prunella modularis) to first investigate whether individuals mate nonrandomly (i.e. assortative mating) with regard to four behavioural traits-flight-initiation distance (FID), provisioning, activity and vigilance-that differ in repeatability and have previously been associated with mating patterns and fitness in other species. Second, we test whether an individual's FID is associated with variability in the dunnocks' mating system (i.e. monogamous pairs vs. polygamous groups). Finally, we determine whether FID and provisioning of males and females associate with their reproductive success. We found no statistical support for assortative mating in FID between males and females. Interestingly, in polygamous groups, co-breeding males differed in their FIDs with dominant alpha males having significantly shorter FIDs compared with subordinate beta-males. Moreover, there was evidence for assortative mating in provisioning for alpha males and females in polygamous groups. We also found that male provisioning influenced reproductive success of both sexes, whereas female provisioning rates only positively correlated with her own but not their partner(s) reproductive output. Our results suggest that personality differences may have important implications for social relationships, the emergence of different mating patterns and ultimately reproductive success within populations.

Female spider aggression is associated with genetic underpinnings of the nervous system and immune response to pathogens.

Identifying the genetic architecture underlying phenotypic variation in natural populations and assessing the consequences of polymorphisms for individual fitness are fundamental goals in evolutionary and molecular ecology. Consistent between-individual differences in behaviour have been documented for a variety of taxa. Dissecting the genetic basis of such behavioural differences is however a challenging endeavour. The molecular underpinnings of natural variation in aggression remain elusive. Here, we used comparative gene expression (transcriptome analysis and RT-PCR), genetic association analysis and pharmacological experiments to gain insight into the genetic basis of aggression in wild-caught jumping spiders (Portia labiata). We show that spider aggression is associated with a putative viral infection response gene, BTB/POZ domain-containing protein 17 (BTBDH), in addition to a putative serotonin receptor 1A (5-HT1A) gene. Spider aggression varies with virus loads, and BTBDH is upregulated in docile spiders and exhibits a genetic variant associated with aggression. We also identify a putative serotonin receptor 5-HT1A gene upregulated in docile P. labiata. Individuals that have been treated with serotonin become less aggressive, but individuals treated with a nonselective serotonin receptor antagonist (methiothepin) also reduce aggression. Further, we identify the genetic variants in the 5-HT1A gene that are associated with individual variation in aggression. We therefore conclude that co-evolution of the immune and nervous systems may have shaped the between-individual variation in aggression in natural populations of jumping spiders.

Zebra finches bi-directionally selected for personality differ in repeatability of corticosterone and testosterone

Consistent between-individual differences in behaviour have been documented across the animal kingdom. Such variation between individuals has been shown to be the basis for selection and to act as a pacemaker for evolutionary change. Recently, equivocal evidence suggests that such consistent between-individual variation is also present in hormones. This observation has sparked interest in understanding the mechanisms shaping individual differences, temporal consistency and heritability of hormonal phenotypes and to understand, if and to what extent hormonal mechanisms are involved in mediating consistent variation in behaviour between individuals. Here, we used zebra finches of the fourth generation of bi-directionally selected lines for three independent behaviours: aggression, exploration and fearlessness. We investigated how these behaviours responded to artificial selection and tested their repeatability. We further tested for repeatability of corticosterone and testosterone across and within lines. Moreover, we are presenting the decomposed variance components for within-individual variance (i.e. flexibility) and between-individual variance (i.e. more or less pronounced differences between individuals) and investigate their contribution to repeatability estimates. Both hormones as well as the exploration and fearlessness but not aggressiveness, were repeatable. However, variance components and hence repeatability differed between lines and were often lower than in unselected control animals, mainly because of a reduction in between-individual variance. Our data show that artificial selection (including active selection and genetic drift) can affect the mean and variance of traits. We stress the importance for understanding how variable a trait is both between and within individuals to assess the selective value of a trait.

Do female rainbow kribs choose males on the basis of their apparent aggression and boldness? A non-correlational mate choice study

Consistent between-individual differences in behaviour, known as personality differences, are heritable and have consequences for individual survival and reproductive success. Therefore, it is likely that personality differences are not just under natural but also under sexual selection. Indeed, the recently developed idea that individuals choose their mate based on its personality finds empirical support. However, most studies on mate choice based on personality traits are correlative pioneering work and there is a paucity of experimental studies that test for causality by disentangling personality measures from other, potentially correlated traits that may be important during mate choice. Here, we tested female preference for the apparent level and consistency of either male aggression (measured as mean distance of approach towards an animated opponent, manipulated by locating males at a fixed distance) or male boldness (measured as activity under a simulated predation threat, manipulated using a gradient in ambient water temperature) in a bi-parental West African cichlid, Pelvicachromis pulcher. Females could observe the apparent behaviour of paired stimulus males and were allowed to choose between the two stimulus males in a subsequent choice test. We found no direct effect of male apparent aggression/boldness on female choice, but an indirect effect such that female preference for the apparently bold male increased with increasing within-male pair contrast in their apparent level of boldness. Our results indicate females consider male boldness per se during mate choice, suggesting male boldness is sexually selected in our study species.Significance statementEver since Darwin introduced the concept of sexual selection, female choice has been studied extensively. However, the hypothesis that consistent between-individual differences in behaviour (known as personality differences) affect mate choice is relatively new. Correlative studies support this idea but provide only suggestive evidence. Here, we used behavioural manipulations in order to disentangle male behaviour from other, potentially correlated male traits, allowing us to test for causality between female choice and personality differences in male aggression and boldness (both in level and consistency of behaviour) in a bi-parental cichlid. We found no overall female preference for male apparent behaviour, but female preference for the bold-appearing male increased with increasing between-male contrast in apparent boldness. Our results indicate a causal link between female choice and male boldness. In future, behavioural manipulations using a temperature gradient could provide further valuable insights.

Males have more aggressive and less sociable personalities than females in semi-captive Asian elephants

Personality, i.e. consistent between-individual differences in behaviour, has been documented in many species. Yet little is known about how males and females of long-lived, highly social species differ in their measures of personality structure. We investigated sex differences in the mean, variance, and covariance of three previously reported personality traits (Attentiveness, Sociability, Aggressiveness) in 150 female and 107 male Asian elephants (Elephas maximus) from a semi-captive population in Myanmar. These three personality traits were obtained by performing exploratory factor analysis on 28 behavioural items that had been rated by experienced elephant handlers. We found that males scored significantly higher on Aggressiveness and tended to score lower on Sociability than females. However, no sex difference was found in the mean scores of Attentiveness. Variances for the three personality traits did not differ between the sexes, suggesting that male and female elephants share the same range of personality variation. Likewise, trait covariances were similar between the sexes. While both sexes show complex sociality in the wild, female Asian elephants typically live in highly social family units, whereas male elephants’ social bonds are weaker. Males usually form dominance ranks by aggressive interactions, especially during musth. Our results on a large sample of individuals living in their natural environment are thus in agreement with elephant life-histories and parallel the findings of sex differences in other long-lived highly social species with similar life-histories.

Brain size predicts behavioural plasticity in guppies (Poecilia reticulata): An experiment.

Understanding how animal personality (consistent between-individual behavioural differences) arises has become a central topic in behavioural sciences. This endeavour is complicated by the fact that not only the mean behaviour of individuals (behavioural type) but also the strength of their reaction to environmental change (behavioural plasticity) varies consistently. Personality and cognitive abilities are linked, and we suggest that behavioural plasticity could also be explained by differences in brain size (a proxy for cognitive abilities), since accurate decisions are likely essential to make behavioural plasticity beneficial. We test this idea in guppies (Poecilia reticulata), artificially selected for large and small brain size, which show clear cognitive differences between selection lines. To test whether those lines differed in behavioural plasticity, we reared them in groups in structurally enriched environments and then placed adults individually into empty tanks, where we presented them daily with visual predator cues and monitored their behaviour for 20days with video-aided motion tracking. We found that individuals differed consistently in activity and risk-taking, as well as in behavioural plasticity. In activity, only the large-brained lines demonstrated habituation (increased activity) to the new environment, whereas in risk-taking, we found sensitization (decreased risk-taking) in both brain size lines. We conclude that brain size, potentially via increasing cognitive abilities, may increase behavioural plasticity, which in turn can improve habituation to novel environments. However, the effects seem to be behaviour-specific. Our results suggest that brain size likely explains some of the variation in behavioural plasticity found at the intraspecific level.

A mechanistic theory of personality-dependent movement behaviour based on dynamic energy budgets.

Consistent between-individual differences in movement are widely recognised across taxa. In addition, foraging plasticity at the within-individual level suggests a behavioural dependency on the internal energy demand. Because behaviour co-varies with fast-slow life history (LH) strategies in an adaptive context, as theoretically predicted by the pace-of-life syndrome hypothesis, mass/energy fluxes should link behaviour and its plasticity with physiology at both between- and within-individual levels. However, a mechanistic framework driving these links in a fluctuating ecological context is lacking. Focusing on home range behaviour, we propose a novel behavioural-bioenergetics theoretical model to address such complexities at the individual level based on energy balance. We propose explicit mechanistic links between behaviour, physiology/metabolism and LH by merging two well-founded theories, the movement ecology paradigm and the dynamic energetic budget theory. Overall, our behavioural-bioenergetics model integrates the mechanisms explaining how (1) behavioural between- and within-individual variabilities connect with internal state variable dynamics, (2) physiology and behaviour are explicitly interconnected by mass/energy fluxes, and (3) different LHs may arise from both behavioural and physiological variabilities in a given ecological context. Our novel theoretical model reveals encouraging opportunities for empiricists and theoreticians to delve into the eco-evolutionary processes that favour or hinder the development of between-individual differences in behaviour and the evolution of personality-dependent movement syndromes.

No male mate choice for female boldness in a bi-parental West African cichlid, the rainbow krib (Pelvicachromis pulcher).

BackgroundIn many species, males have a lower reproductive investment than females and are therefore assumed to increase their fitness with a high number of matings rather than by being choosy. However, in bi-parental species, also males heavily invest into reproduction. Here, reproductive success largely depends on costly parental care; with style and amount of parental effort in several cases being associated with personality differences (i.e., consistent between-individual differences in behaviour). Nonetheless, very little is known about the effect of personality differences on (male) mate choice in bi-parental species.MethodsIn the present study, we tested male mate choice for the level and consistency of female boldness in the rainbow krib, Pelviachromis pulcher, a bi-parental and territorial West African cichlid. Individual boldness was assumed to indicate parental quality because it affects parental defence behaviour. For all males and females, boldness was assessed twice as the activity under simulated predation risk. Mate choice trials were conducted in two steps. First, we let a male observe two females expressing their boldness. Then, the male could choose between these two females in a standard mate choice test.ResultsWe tested for a male preference for behavioural (dis-)similarity vs. a directional preference for boldness but our data support the absence of effects of male and/or female boldness (level and consistency) on male mating preference.DiscussionOur results suggest female personality differences in boldness may not be selected for via male mate choice.

Social conformity in solitary crabs, Carcinus maenas, is driven by individual differences in behavioural plasticity

Group living is widespread in the animal kingdom and recent studies into the mechanisms underlying group cohesion and behavioural synchrony have highlighted the importance of between-individual behavioural differences (‘animal personality’). In group-living animals, social conformity occurs when animals compromise their own behaviour to the level of a certain behaviour displayed by another individual or a group, and the degree to which individuals conform can depend upon interindividual differences in behavioural types. Social conformity can increase group cohesion and ultimately predator avoidance and/or resource acquisition for group-living individuals. However, it remains unclear whether similar conformity effects exist in solitary species, many of which form temporary aggregations and, if so, whether changes in behaviour in the presence of conspecifics are dependent on individuals' personalities in solitary contexts. We studied the effects of social context (i.e. the presence of a conspecific) on behaviour in solitary shore crabs, using automated video tracking. Individuals differed consistently in their activity levels within and across contexts and were significantly more active in solitary than dyadic contexts. No differences in activity between same- and opposite-sex dyads were found. Crabs' activity levels were more similar when tested together than when tested alone, indicating a social conformity effect. Furthermore, more active behavioural types decreased their activity to a greater extent when paired with a conspecific. The sex composition of the dyad had no effect on changes in activity. Overall, our findings suggest that social conformity is moderated by individual behavioural differences in a solitary organism. It is often presumed that, over evolutionary time, the social structure of animal populations has important consequences for the evolution of personalities and vice versa. We suggest that studying solitary or facultatively social organisms may allow researchers to tease out causality between personality differences and socioecological dynamics.

Body size predicts between-individual differences in exploration behaviour in the southern corroboree frog

Proximate mechanisms underpinning between-individual variation in repeatedly expressed behaviours (animal personality) remain poorly understood. Recent theoretical models have focused on the concept of adaptive state-dependent behaviour, proposing that repeatable differences in behaviour emerge due to individual differences in repeatable state variables such as metabolic rate, age, sex or body size. Few studies have attempted to investigate the effect of state on personality empirically, and evidence for links between individual variation in state and personality remains equivocal. We used a captive colony of southern corroboree frogs, Pseudophryne corroboree , to (1) test for innate, temporally repeatable behavioural differences (animal personality) along the activity, exploration/avoidance and boldness/shyness behavioural axes, (2) test for behavioural syndromes (between-individual correlations between behavioural traits) and (3) determine whether behavioural traits are correlated with body size at the between-individual level. Individuals exhibited repeatable variation along all three behavioural axes, but between-individual correlations did not deviate from zero, providing no evidence for behavioural syndromes. Body size explained 40% of the between- individual variance in exploration behaviour, with larger frogs exhibiting greater mobility and travelling further in a novel environment. These associations indicate that there is potential for innate body size variation in P. corroboree to act as an important state variable underpinning repeatable between-individual behavioural differences. Future research may test this idea experimentally. Continued investigation of state-dependent individual behaviour in P. corroboree and other animals is likely to provide important insights into the proximate causes of animal personality.

Development of behavioural profile in the Northern common boa (Boa imperator): Repeatable independent traits or personality?

Recent studies of animal personality have focused on its proximate causation and ecological and evolutionary significance in particular, but the question of its development was largely overlooked. The attributes of personality are defined as between-individual differences in behaviour, which are consistent over time (differential consistency) and contexts (contextual generality) and both can be affected by development. We assessed several candidates for personality variables measured in various tests with different contexts over several life-stages (juveniles, older juveniles, subadults and adults) in the Northern common boa. Variables describing foraging/feeding decision and some of the defensive behaviours expressed as individual average values are highly repeatable and consistent. We found two main personality axes—one associated with foraging/feeding and the speed of decision, the other reflecting agonistic behaviour. Intensity of behaviour in the feeding context changes during development, but the level of agonistic behaviour remains the same. The juveniles and adults have a similar personality structure, but there is a period of structural change of behaviour during the second year of life (subadults). These results require a new theoretical model to explain the selection pressures resulting in this developmental pattern of personality. We also studied the proximate factors and their relationship to behavioural characteristics. Physiological parameters (heart and breath rate stress response) measured in adults clustered with variables concerning the agonistic behavioural profile, while no relationship between the juvenile/adult body size and personality concerning feeding/foraging and the agonistic behavioural profile was found. Our study suggests that it is important for studies of personality development to focus on both the structural and differential consistency, because even though behaviour is differentially consistent, the structure can change.

Different or alike? Female rainbow kribs choose males of similar consistency and dissimilar level of boldness

Although the existence of consistent between-individual differences in behaviour (‘personality differences’) has been well documented during the last decade, the adaptive value of such behavioural limitations remains an open field for researchers of animal behaviour. Personalities clearly restrict individuals in their ability to adjust their behaviour to different conditions. However, sheer costs of flexibility cannot explain the polymorphism created by personality variation. In a correlative approach, we here tested whether mate choice might act as a major driving force maintaining personality variation in the monogamous, biparental rainbow krib, Pelvicachromis pulcher. We personality-typed all males and females for their boldness (activity under simulated predation risk) and allowed females to choose between two males that differed in their boldness (behavioural level and consistency). Prior to the choice, females were allowed to observe both males, expressing their natural boldness towards a video-animated natural predator. Both sexes showed personality differences in boldness over the short and long term. Furthermore, when removing side-biased females, we found a disassortative mating preference for the behavioural level and an assortative preference for behavioural consistency in boldness. These preference patterns might facilitate effective parental role allocation during offspring care and/or provide genetic benefits. Our results suggest that sexual selection plays an important role in the evolution of personality differences.

Pace of life and behaviour: rapid development is linked with increased activity and voracity in the wolf spider Pardosa agrestis

Modern life history theory hypothesizes that pace of life is a strong predictor of life history traits. Recently, the notion that life history studies should integrate animal behaviour has emerged, because between-individual differences in behaviour are often coupled with fitness differences. So far, studies have mainly focused on interspecies or interpopulation perspectives, and research on the effects of life history differences on individual behaviour remain scarce. In the present study we aimed to contribute to the understanding of how pace of life is related to consistent individual behaviour. We investigated the relationship between developmental speed and consistent behaviour of the field wolf spider, Pardosa agrestis. In this species, individuals originating from the same clutch can typically follow either a slow or a rapid developmental pathway, characterized by a developmental time of about 10 or 3 months, respectively. We found that spiders, regardless of their developmental speed, behaved consistently in most of the tests. Our results also show that individuals developing rapidly were significantly more active during exploration and more successful in prey-catching tests than slowly developing spiders. Although rapidly developing spiders were bolder in one of the tests, this difference did not persist over the repeated measurements. Our work seems to support the notion that pace of life and animal personality are correlated, and pace of life might predict the behavioural types of individuals.

Repeatability and consistency of individual behaviour in juvenile and adult Eurasian harvest mice

Knowledge on animal personality has provided new insights into evolutionary biology and animal ecology, as behavioural types have been shown to affect fitness. Animal personality is characterized by repeatable and consistent between-individual behavioural differences throughout time and across different situations. Behavioural repeatability within life history stages and consistency between life history stages should be checked for the independence of sex and age, as recent data have shown that males and females in some species may differ in the repeatability of behavioural traits, as well as in their consistency. We measured the repeatability and consistency of three behavioural and one cognitive traits in juvenile and adult Eurasian harvest mice (Micromys minutus). We found that exploration, activity and boldness were repeatable in juveniles and adults. Spatial recognition measured in a Y Maze was only repeatable in adult mice. Exploration, activity and boldness were consistent before and after maturation, as well as before and after first sexual contact. Data on spatial recognition provided little evidence for consistency. Further, we found some evidence for a litter effect on behaviours by comparing different linear mixed models. We concluded that harvest mice express animal personality traits as behaviours were repeatable across sexes and consistent across life history stages. The tested cognitive trait showed low repeatability and was less consistent across life history stages. Given the rising interest in individual variation in cognitive performance, and in its relationship to animal personality, we suggest that it is important to gather more data on the repeatability and consistency of cognitive traits.

Food and vitamin D3 availability affects lizard personalities: an experiment

It has been proposed recently that labile state variables (e.g. energy reserves) can have a key role in the development and maintenance of consistent between-individual behavioural variation (i.e. animal personality) within population. In male Carpetan rock lizards (Iberolacerta cyreni), the provitamin D3 component of femoral gland secretion acts as an honest signal in sexual communication. Further, vitamin D3 has many important metabolic functions in reptiles. Therefore, by employing a factorial experiment with food (high vs. low) and vitamin D3 (supplemented vs. control) treatments in wild-caught reproductive male I. cyreni, we tested whether changing labile components of individual state affected (i) behavioural consistency (the degree of between-individual difference) and (ii) behavioural type (mean behaviour). Animal personality in activity was present in all treatments; however, personality was present only in the high food × vitamin D3 supplementation treatment in shelter use and it was present in all but the low food × placebo treatment in risk taking. Lizards (i) decreased activity in the high food treatment, (ii) increased shelter use in the vitamin D3 supplementation treatment and (iii) increased risk taking in the low food × vitamin D3 supplementation treatment. We conclude that short-term changes in individual state affect both behavioural consistency and behavioural type of reproductive male I. cyreni. Unfavourable conditions resulted in decreased behavioural consistency, while high-state individuals became less active in general. Individuals with high specific (vitamin D3) but low general (energy reserves) state took higher risk. We discuss several evolutionary explanations for the reported patterns. The evolutionary and developmental mechanisms resulting in consistent between-individual behavioural differences across time and situations (i.e. animal personality) are of high scientific interest. It has been recently proposed that links between individual state (e.g. how well-fed the individual is) and behaviour can maintain such between-individual differences even on an evolutionarily timescale. However, whether short-term state changes are able to affect animal personality in adults is an open question. In a manipulative experiment, we found that the amount of food and vitamin D3 (known to increase physiological quality and attractiveness of male Carpetan rock lizards, I. cyreni) affected the expression of animal personality and the actual behavioural types of reproductive male Carpetan rock lizards. Therefore, we provide evidence that short-term environmental variation does induce or suppress animal personality, and it also affects individual behaviour.

Habitat preference of wormlions and their behavioural repeatability under illumination/shade conditions

1. Animal personality is defined as the repeatable between-individual differences in behaviour over time and contexts. Some personality traits, such as activity or aggression, have received much attention while other behaviours, such as habitat preference or learning, have been neglected. 2. Wormlion larvae are sit-and-wait dipteran predators that inhabit shaded microhabitats in the field and also prefer shade in the laboratory. The aim of the present study was to examine wormlion larvae behavioural repeatability in general and specifically in the context of habitat preference. In order to achieve this, three experiments were conducted to determine whether, to what extent and under which conditions wormlion preference for shaded microhabitats is repeatable. 3. Individual tendency to relocate when the environment conditions deteriorate was also assessed, by switching between shaded and illuminated conditions, either with or without pit destruction. 4. Larvae showed a highly repeatable preference for shade. Repeatability was detected in additional behavioural traits: pit construction, pit area and tendency to relocate. 5. This behavioural repeatability was demonstrated under constant microhabitat conditions, with distinct behaviours in each setting. Under constant illumination, wormlions constructed smaller pits, moved over longer distances and were found at the tray edges more frequently than under constant shade conditions, suggesting that illuminated environments are perceived as risky or unsuitable. 6. Switching between the two microhabitat conditions without pit destruction induced fewer relocations than switching with pit destruction, suggesting that wormlions do not tend to abandon their pits, even if their microhabitat conditions deteriorate.

Tank size alters mean behaviours and individual rank orders in personality traits of fish depending on their life stage

Animals adjust their behaviour over time and contexts to cope with ecological and environmental variation. However, the presence of consistent between-individual differences in behaviour (i.e. personality) suggests that individual behaviour may be less flexible than previously thought. Here, we tested whether the size of the experimental tank and the ontogenetic stage of individuals affect estimates of average and consistent individual variation in activity and risk-taking behaviours in the eastern mosquitofish, Gambusia holbrooki, a fish model widely utilized for behavioural research. We measured risk taking and activity in juvenile, subadult and adult mosquitofish in a standard open-field test, in which the size of test tank varied linearly. We found strong evidence that spatial constraints alter mosquitofish behaviour. In particular, we observed that average activity increased with tank size, while the willingness of fish to take risks was independent of tank size. Moreover, juvenile fish exhibited, on average, lower risk-taking behaviours than older individuals. We highlight that the use of differently sized tanks may result in unequal variation in the average behaviour between juvenile and older fish, with escaping abilities of juvenile fish being underestimated in small environments. Most interestingly, we observed that variation in tank size triggered changes in the individual rank order for both risk taking and activity in juvenile fish, thus altering their personality estimates. In contrast, adult fish maintained consistent individual rank orders across all tank sizes. This study supports the hypothesis that behavioural repeatability increases with age, suggesting that personality estimates on adult animals may be less vulnerable to variation in laboratory contexts than those on juvenile ones.

Unravelling the Philosophies Underlying ‘Animal Personality’ Studies: A Brief Re-Appraisal of the Field

The last decade has seen lots of studies on ‘animal personality’ (i.e. the study of consistent between-individual behavioural differences). As timely and promising as this field is, its development has come with a diversity of research questions. As an unfortunate consequence, it now suffers from substantial confusion about what ‘animal personality’ is, and how relevant related research frameworks are. Here, we stress the current inconsistencies and sources of confusion pertaining to the field, and their consequences on terminology used and miscommunication between researchers. In an attempt to unravel and clarify the concepts underlying the field, we identify two distinct, but complementary, theory-driven conceptual frameworks: the intra-individual variability (IIV) approach and the life-history (LH) approach, which we believe encompass the vast majority of existing ‘personality studies’. Finally, we argue in favour of theory-driven studies of consistent behavioural differences and state that the integrative statistical properties of random regression models should not override the merit of alternative conceptual frameworks. We then provide brief guidelines and warnings for a parsimonious and sound use of terminology.

No Association between Personality and Candidate Gene Polymorphisms in a Wild Bird Population.

Consistency of between-individual differences in behaviour or personality is a phenomenon in populations that can have ecological consequences and evolutionary potential. One way that behaviour can evolve is to have a genetic basis. Identifying the molecular genetic basis of personality could therefore provide insight into how and why such variation is maintained, particularly in natural populations. Previously identified candidate genes for personality in birds include the dopamine receptor D4 (DRD4), and serotonin transporter (SERT). Studies of wild bird populations have shown that exploratory and bold behaviours are associated with polymorphisms in both DRD4 and SERT. Here we tested for polymorphisms in DRD4 and SERT in the Seychelles warbler (Acrocephalus sechellensis) population on Cousin Island, Seychelles, and then investigated correlations between personality and polymorphisms in these genes. We found no genetic variation in DRD4, but identified four polymorphisms in SERT that clustered into five haplotypes. There was no correlation between bold or exploratory behaviours and SERT polymorphisms/haplotypes. The null result was not due to lack of power, and indicates that there was no association between these behaviours and variation in the candidate genes tested in this population. These null findings provide important data to facilitate representative future meta-analyses on candidate personality genes.

Cooperative personalities and social niche specialization in female meerkats

The social niche specialization hypothesis predicts that group-living animals should specialize in particular social roles to avoid social conflict, resulting in alternative life-history strategies for different roles. Social niche specialization, coupled with role-specific life-history trade-offs, should thus generate between-individual differences in behaviour that persist through time, or distinct personalities, as individuals specialize in particular nonoverlapping social roles. We tested for support for the social niche specialization hypothesis in cooperative personality traits in wild female meerkats (Suricata suricatta) that compete for access to dominant social roles. As cooperation is costly and dominance is acquired by heavier females, we predicted that females that ultimately acquired dominant roles would show noncooperative personality types early in life and before and after role acquisition. Although we found large individual differences in repeatable cooperative behaviours, there was no indication that individuals that ultimately acquired dominance differed from unsuccessful individuals in their cooperative behaviour. Early-life behaviour did not predict social role acquisition later in life, nor was cooperative behaviour before and after role acquisition correlated in the same individuals. We suggest that female meerkats do not show social niche specialization resulting in cooperative personalities, but that they exhibit an adaptive response in personality at role acquisition.