Personality and social environment predict cognitive performance in common marmosets (Callithrix jacchus)

An exploratory study of behavioral traits and the establishment of social relationships in female laboratory rats

There is growing evidence that social relationships influence individual fitness through various effects. Clarifying individual differences in social interaction patterns and determinants for such differences will lead to better understanding of sociality and its fitness consequences for animals. Behavioral traits are considered one of the determining factors of social interaction. The purpose of this study was to explore the effects of individual behavioral traits on social relationship building in laboratory rats (Rattus norvegicus), a highly social species. Initially, the following behavioral characteristics were measured in individuals: tameness (glove test), activity (open field test), exploration (novel object test), sociability (three-chamber test), and boldness (elevated plus maze test). We then used DeepLabCut to behaviorally track three groups of four individuals (12 total) and analyze social behaviors such as approach and avoidance behaviors. Principal component analysis based on behavioral test results detected behavioral traits interpreted as related to exploration, boldness, activity, and tameness, but not sociability. In addition, behavioral tracking results showed consistent individual differences in social behavior indices such as isolation time and partner preference. Furthermore, we found that different components were correlated with different phases of social behavior; exploration and boldness were associated with the early stages of group formation, whereas activity was associated with later stages of relationship building. From these results, we derived hypothesize that personality traits related to the physical and social environment have a larger influence in the relationship formation phase, and the behavioral trait of activity becomes important in the maintenance phase of relationships. Future studies should examine this hypothesis by testing larger group sizes and ensuring there is less bias introduced into group composition.

Assessing Eysenck's PEN model to describe personality in chimpanzees

Questionnaires adapted from human models can be used to reliably assess personality also in non-human primates. In this study, we used an adapted version of Eysenck's Psychoticism-Extraversion-Neuroticism (PEN) model that focuses on three higher-order personality traits. Extending previous work on a small group of chimpanzees (Pan troglodytes), we tested 37 chimpanzees housed at Fundació Mona (Girona, Spain) and the Leipzig Zoo (Germany). We assessed personality with a 12-item questionnaire, which raters scored using a 7-point Likert scale. To identify the personality traits, we conducted data reduction with Principal Components Analysis and Robust Unweighted Least Squares. The ICCs for the single (3, 1) and average (3, k) ratings indicated substantial agreement between raters. Parallel analyses identified two factors to retain, whereas the scree plot inspection and eigenvalues larger than one rule identified three factors. Factor 1 and 2 in our study were identical to the ones previously described for this species (labelled Extraversion and Neuropsychoticism, respectively) and we also obtained a third factor that could be related to Dominance (Fearless Dominance). Thus, our results confirm the potential of the PEN model to describe chimpanzee personality structure.

Prosociality and reciprocity according to parental status, communication, and personality in domestic canaries (Serinus canaria)

Prosociality (behaviours that benefit to a recipient without necessarily involving a cost to the actor) has recently been shown to exist in various taxa, including birds. Studies on prosociality in primates found that prosocial tendencies of the subject could be related to sex and parental care, communication from the recipient, cognitive abilities and personality. To investigate the existence of such associations on birds, we conducted a Prosocial Choice Task with domestic canaries (Serinus canaria). In our experiment, the subject could choose between three options: a prosocial, a selfish, and a null option (with no cost for the subject). We also conducted a food sharing experiment and measured several personality traits. Our results highlighted high levels of prosociality and a tendency to reciprocity among reproductive mates. We found a higher propensity to be prosocial in nulliparous individuals than in individuals that have previously been parents, but better sharing abilities in parents than in nulliparous individuals. When they were recipient, parents also used communication more efficiently than nulliparous subjects. Data suggest that parental expertise could enhance subjects' skills in eliciting prosociality. We also highlighted some interaction between prosociality, learning abilities, and some personality traits, proactive individuals being fast learners and more prosocial, while reactive individuals being slow learners and more reciprocal. Our results suggest that prosociality and reciprocity could be linked to personality and cognitive abilities, and that it might be interesting to consider them as parts of individual's cognitive style.

Age, but not hand preference, is related to personality traits in common marmosets (Callithrix jacchus)

The proximate mechanisms underlying animal personalities, i.e. consistent inter-individual differences in behaviour, are a matter of discussion. Brain lateralization, expressed as the preferred use of the contralateral limb, has been suggested as one of these mechanisms. In this study, we measured a proxy of brain lateralization in captive common marmosets (N = 28) by testing hand preference in a simple food-reaching task and evaluated personality by coding a wide range of behaviours observed in daily situations. We explored the links between personality and both direction and strength of hand preference, as well as age and sex, using linear models. Principal component analysis revealed that the stable behavioural variables were organized in three personality dimensions: Agreeableness, Extraversion and Neuroticism. Regarding hand preference, 14 individuals were left-handed, seven were right-handed and seven were ambilateral. Contrary to our predictions, we did not find any relationship between personality scores and hand preference or sex. Instead, age was a significant predictor of personality scores, with older individuals being more agreeable and less extraverted. The link between brain lateralization and personality seems to be equivocal and dependent on personality and brain lateralization assessment methods. Further examinations of other proximate mechanisms, such as physiology or (epi)genetics, may elucidate what drives personality variation in common marmosets.

The marmoset as a model for investigating the neural basis of social cognition in health and disease

Social-cognitive processes facilitate the use of environmental cues to understand others, and to be understood by others. Animal models provide vital insights into the neural underpinning of social behaviours. To understand social cognition at even deeper behavioural, cognitive, neural, and molecular levels, we need to develop more representative study models, which allow testing of novel hypotheses using human-relevant cognitive tasks. Due to their cooperative breeding system and relatively small size, common marmosets (Callithrix jacchus) offer a promising translational model for such endeavours. In addition to having social behavioural patterns and group dynamics analogous to those of humans, marmosets have cortical brain areas relevant for the mechanistic analysis of human social cognition, albeit in simplified form. Thus, they are likely suitable animal models for deciphering the physiological processes, connectivity and molecular mechanisms supporting advanced cognitive functions. Here, we review findings emerging from marmoset social and behavioural studies, which have already provided significant insights into executive, motivational, social, and emotional dysfunction associated with neurological and psychiatric disorders.