Consistent 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.

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.

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.

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.

How does temperature affect behaviour? Multilevel analysis of plasticity, personality and predictability in hermit crabs

When animals are observed on multiple occasions, consistent between-individual differences in behaviour, often referred to as animal personality, may be observed. However, this does not mean that the behaviour of a given individual is readily predictable. While some individuals show low levels of variation around their behavioural mean, others show high levels of variation, and there may be significant between-individual differences in this intraindividual variation (‘IIV’) in behaviour. While it has been suggested that IIV might reduce susceptibility to predators, little is known about the functions or causation of IIV. We investigated the effects of temperature on the startle response duration of hermit crabs, Pagurus bernhardus. For poikilothermic animals, temperature has a direct and multiplicative influence on metabolic rate, which in turn is expected to influence behaviour because of its effect on energy requirements. At the level of mean startle response durations, the effect of temperature was dependent on treatment order; within treatment orders, individuals showed different reaction norms. In contrast, at the level of IIV, while the presence of significant between-individual differences was dependent on treatment order, there was a clear unidirectional effect in both treatment orders for individuals to be less predictable at higher temperature. Thus, predictability in behaviour appears to vary with a key environmental variable that is known to influence energy requirements and potentially the level of risk that individuals are willing to accept.

Collective personalities in honeybee colonies are linked to colony fitness

Personality differences (i.e. consistent between-individual differences in behaviour) play an important role in the lives of humans and other animals, influencing both their day-to-day actions and their long-term reproductive success. For organisms living in highly structured groups of related individuals, such as colonies of social insects, personalities could also emerge at the group level. However, while numerous recent studies have investigated individual-level personality, the phenomenon of collective personality in animal groups has received little attention. In this paper, we apply the concept of collective personality to colonies of honeybees (Apis mellifera). We document the presence of consistent differences among colonies across a wide range of collective behaviours and demonstrate a link between colony-level personality traits and fitness. The colonies in our study showed consistent behavioural differences in traits such as defensive response, foraging activity and undertaking, and several of these traits were correlated as part of a behavioural syndrome. Furthermore, some of these traits were strongly tied to colony productivity and winter survival. Our results show that the concept of collective personality is applicable to colonies of social insects, and that personality differences among colonies can have important consequences for their long-term survival and reproduction. Applying the concept of personality to close-knit animal groups can provide important insights into the structure of behavioural variability in animal populations and the role that consistent between-group behavioural differences play in the evolution of behaviour.

Effects of shell size on behavioural consistency and flexibility in hermit crabs

Animal personalities are assumed to be present when there are consistent between-individual differences in behaviour, whereas behavioural flexibility occurs when individual responses are continuously adjusted. Where both possibilities have been tested for, individuals may show both behavioural consistency and flexibility. Therefore, to gauge the importance of consistent individual differences in behaviour, it is useful to compare the strength of consistency with that of plasticity in behaviour. Here we investigate startle responses in hermit crabs ( Pagurus bernhardus (L., 1758)) in high- and low-risk situations. We vary the level of risk between situations by manipulating the quality of empty gastropod shells available to the crabs. Comparison of statistical effect size estimates for tests of concordance and difference between situations reveals a strong pattern of consistent between-individual differences in behaviour in comparison to a statistically significant but reactively weak pattern of behavioural flexibility. Although the startle duration varied, on average, in crabs from different sites, this was mainly due to different responses during an in situ phase of the experiment.