Individual differences in nonhuman primates: personality and its relationship to social interactions, socio-emotional perception, and well-being
Wilson, Vanessa Amy Davina
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In recent years there have been efforts to assess associations between personality, longevity and well-being in nonhuman primates. Currently, findings indicate that, as in humans, personality traits such as extraversion are associated with both higher well-being (in monkeys and apes) and longevity (in gorillas). Why certain traits seem to have a protective effect is not yet well understood. One hypothesis is that more extraverted individuals rely on the company of others to alleviate stress, and thus mediate physiological stressors, increasing potential life span. Individual differences in social behaviour are therefore an important consideration for increasing our understanding of the protective effects of personality traits. The role of personality in social interactions and well-being is the main focus of this thesis. In Chapter 2, I assess personality and well-being in two species of New World monkey - common (Saimiri sciureus) and Bolivian squirrel monkeys (Saimiri boliviensis) - for which these associations have not previously been studied. I assess differences in personality trait structure between the two species, and compare them to a close relative, Sapajus apella (brown capuchins). I also correlate personality with well-being. Results show that both squirrel monkey species are similar in personality structure, but Bolivian squirrel monkeys share more similar traits with brown capuchins than common squirrel monkeys do. Well-being is associated with low Neuroticism and high Openness. These comparisons inform our understanding of the phylogeny of personality traits, as well as the ancestral links between personality and well-being. In Chapter 3 I focus on examining individual differences in chimpanzee (Pan troglodytes) traits, through the use of previously collected personality data, which may reflect something akin to autism in nonhuman primates. In Chapter 4 I examine behavioural correlates of these traits, and assess personality in relation to behaviour. Results indicate that personality is a stronger predictor of individual differences in social behaviour than the scale measuring autism-like traits. Continuing with a focus in chimpanzees, in Chapter 5 I examine whether personality predicts how individual chimpanzees perceive emotion in conspecifics, using both behavioural and experimental data. Findings show that individuals differ in their attention and arousal in response to emotions in others, and that personality plays a role in these responses. I also report different ‘levels’ of response indicative of separate arousal and attention based processes. This is an understudied but important area of research that might help to elucidate differences in coping with stressful situations in a group environment. In Chapter 6 I shift from a focus of personality as a predictor of response, to potential signals of personality, by examining personality correlates of facial morphology in brown capuchins, Sapajus apella. Results indicate that face width is associated with higher Assertiveness, whilst lower face height is associated with higher Neuroticism/lower Attentiveness. To assess the theory that these associations may act as social cues, such as signals of status or mate quality, in Chapter 7 I assess whether capuchins perceive differences in face width of conspecifics by measuring response to facial images. Results suggest that capuchins do not differ between wide and narrow faces. I discuss the possibility that perception of these associations may be dependent on other variables such as age or knowledge of the signal receiver. Overall, this thesis takes a broad approach to understanding personality, by examining its role in social interactions, perception of others and well-being. These findings are discussed in light of both evolutionary theory and potential benefits to welfare.