Personality, that is intra-individual consistency and inter-individual variation in behaviour, is widespread throughout the animal kingdom. This challenges traditional evolutionary assumptions that selection should favour behavioural flexibility, and that variation in behavioural strategies reflects stochastic variation around a single optimal behavioural strategy. Adaptive models to explain personality within the framework of evolutionary and behavioural ecology exist, and are typically empirically explored by identifying proximate associations to, and the functional consequences of, personality expression. To date, such studies have typically quantified a narrow range of personality traits within a species, and focused on captive populations or species with relatively limited behavioural or social repertoires. In this thesis, personality is studied in wild Barbary macaques (Macaca sylvanus). Quantification of personality structure in the species was conducted using a multi-method approach, and subsequently, it was examined whether physiological stress response (a proximate association) was related to personality expression, and whether personality expression affected social (functional) outcomes for individuals. Seven personality constructs were identified in Barbary macaques. Three personality constructs were related to physiological stress responses (Excitability, Tactility and Exploration), with the relationship between stress and personality expression dependent on sex, and in some cases rank or age. Two personality constructs (Excitability and Exploration) were associated with measures of social integration. Subjects generally socially assorted themselves according to personality, tending to be in proximity to individuals with a similar personality to themselves. This study contributes methodologically by demonstrating the plausibility of multi-method approaches to measuring personality in wild primates, and empirically, by generating evidence supporting adaptive models for the evolution of personality, namely that intra-individual consistency in behaviour may be mediated by physiology and that inter-individual variation in behaviour has functional benefits in the formation of social relationships and social structures.

A full understanding of any biological trait requires investigation of its evolutionary origin. Primates inspire great curiosity amongst researchers due to the remarkable diversity across species in both anatomical and behavioural traits, including sociality, sexual behaviour, life histories, neuro-anatomy, cognitive abilities and behavioural repertoires. The study of primates has involved comparative approaches since its inception, however, the necessary tools for statistically investigating the macro-evolutionary processes responsible for current diversity in biological traits have been developed only in the last 30 years or so, namely phylogenetic reconstruction and phylogenetic comparative methods. Amongst a multitude of evolutionary questions that can be addressed by phylogenetic comparative analyses, this thesis attempts to address two in particular, concerning primates. First, chapters 3 and 4 use meta-analysis and phylogenetic comparative analyses to investigate the evolution of large, brightly coloured ‘exaggerated sexual swellings' in female Catarrhine (‘Old World') primates. Together, chapters 3 and 4 show that such swellings are signals of temporal fertility, and present evidence to suggest that swellings co-evolved with conditions favouring male mate choice and cryptic female choice, therefore shedding light on the general conditions under which female signals of temporal fertility should evolve. Second, chapters 5 and 6 use phylogenetic comparative analyses investigate the evolution of enlarged brain size in the primate order. Together, chapters 5 and 6 suggest that multiple selection pressures have contributed to diversity in brain size and cognitive traits across primates, including sociality, intra-sexual competition and extended life history. Further, analyses presented in chapter 6 suggest that reliance on learned behaviour is a self-reinforcing evolutionary process, favouring ‘runaway' increases in cognitive abilities and reliance on culture in some primate lineages, which parallels increases in brain size, cognitive ability and reliance on culture in human evolution.

This thesis uses a number of novel methods to investigate how various measures of individual energetic status and condition vary within and between two troops of olive baboons (Papio hamadryas anubis) in Gashaka Gumti National Park, Nigeria. One troop is entirely wild-feeding whilst the other supplements its diet with crop-raiding, behaviour previously suggested to provide energetic benefits. Observations of activity budgets and feeding behaviour were combined with nutritional analyses of food samples to estimate energetic intake and expenditure amongst adult female baboons. Glucocorticoid (stress hormone), progesterone (reproductive hormone) and urinary C-peptide (an indicator of energetic status) levels of the same animals were assessed via analyses of faecal and urine samples. These data were used to investigate the effect of food-enhancement, between troops; the effect of reproductive state and rank, within troops; and the effect of variation in weather conditions and food availability across the nine month study period. Benefits of crop-raiding behaviour included elevated resting time, energy intake rates and reproductive success, and reduced feeding time and glucocorticoid levels in the crop-raiding troop as compared to the wild-feeding troop. Food-enhancement also appears to have buffered the crop-raiding troop’s energetic status and stress levels against the effects of environmental stressors. Within troops, energy intake and expenditure rates varied between individuals in different reproductive states but not different ranks and neither factor significantly affected C-peptide or glucocorticoid levels. Rainfall had a considerable but variable influence on the baboons, being correlated with both positive and negative aspects of their behaviour and condition. Gashaka represents an extreme habitat for baboons, with high rainfall creating both a food and disease rich environment. The results of this study suggest that while low to moderate rainfall brings benefits, via increased food availability, heavy rainfall exerts a negative influence on the Gashaka baboons via increased disease risk.

Les macaques sont-ils capables de prendre en compte le préjudice porté à autrui occasionné par leurs actes ? Si oui, quelles facultés leur permettent de l'appréhender et quelles variables influenceraient leurs décisions dans de tels contextes sociaux ? De la perception à la production de comportements sociaux, une multitude de processus mentaux complexes permettent aux macaques de vivre au sein d'une société dynamique, structurée et cohésive. Bien que la présence de comportements pro et antisociaux y ait déjà été décrite, leurs causes ultimes et proximales ne sont pas évidentes. Est-ce que l'empathie, définie ici comme la capacité à ressentir les émotions d'autrui, pourrait expliquer l'expression de comportements prosociaux ? Les réponses à de telles questions peuvent avoir des répercussions importantes pour les sciences, mais aussi pour la philosophie et l'éthique. L'originalité et la pertinence de notre démarche expérimentale résident dans la mesure objective des comportements sociaux à l'aide de dispositifs et protocoles novateurs conçus et validés au cours de cette thèse. Nous avons en effet entrepris de reproduire un contexte social dans un environnement contrôlé de laboratoire. Ainsi, en plaçant deux animaux face à face, nous avons mis au point un protocole de décision sociale unique permettant à un macaque acteur de choisir de délivrer soit un stimulus aversif (un jet d'air comprimé sur le visage) soit un stimulus appétitif (une goutte de jus de fruit) à son partenaire, à un espace vide ou à lui-même. Les choix étant organisés en paires, l'acteur devait sélectionner soit l'option prosociale, soit l'option antisociale ou, pour des décisions contrôles non-sociales, soit l'option rationnelle, soit l'option irrationnelle. Des analyses appropriées des mesures oculométriques (niveau de regard mutuel et fréquence de clignement des yeux) nous ont permis d'établir des relations entre réponses émotionnelles et tendances pro- (ou anti-) social et de révéler des processus homologues à ceux impliqués dans l'empathie émotionnelle humaine, car dépendants des expériences passées et des relations entretenues avec le partenaire / Do macaques are able to take into account others' welfare during social decisions-making ? If so, what capacities allow them to apprehend it and which variables would influence their decisions in such social contexts ? From perception to the production of social behavior, a multitude of complex mental processes allow macaques to live in a dynamic society, structured and cohesive. Although the presence of pro-and antisocial behavior had already been described, their ultimate and proximate causes are not known. Does empathy, defined here as the ability to feel the emotions of others, could explain the expression of pro-social behavior? The answers to such questions might have important implications for science, but also in philosophy and ethics. The originality and relevance of our experimental approach lies in the objective measurement of social behavior using innovative devices and protocols developed and validated during this thesis. Indeed, we aimed to reproduce a social context in a controlled laboratory environment. Thus, by placing two animals face to face, we have developed a unique protocol for social decision allowing a macaque to delivered either an aversive stimulus (an air puff on the face), an appetitive stimulus (drop of fruit juice) to its partner, to an empty space or to itself. The choices are organized in pairs, the actor had to select either the prosocial option or antisocial option or, for non-social controls decision the rational or irrational option. Appropriate analyzes of eye tracking measures (level of mutual gaze and blink frequency) allowed us to establish relationships between emotional responses and pro (or anti) social trends. It revealed processes dependent on past experiences and relationships with the partner, thus homologous to those involved in human emotional empathy

This thesis examines the relationship between individual differences in learning, personality, and social success in two groups of brown capuchin monkeys (Sapajus sp.) housed at the “Living Links Centre for Human Evolution” at Edinburgh Zoo, UK. Being able to learn quickly and efficiently likely helps primates achieve social success (defined here in terms of centrality within a social network), such as acquiring knowledge of others or learning social skills. Therefore, individuals that are better at learning were predicted to have greater social success than other group members. This prediction, however, contrasts with hypotheses generated from two other disciplines at the individual level: 1) the study of behavioural innovation, and 2) the study of individual differences, i.e. “personality”. In terms of behavioural innovation, better learners should have less social success than other group members because they are expected to rely more on problem-solving, rather than physical combativeness or status, to gain access to socioecological resources. In terms of personality, learning should have little or no direct relationship with social success because other individual differences, like sociability and fearfulness, should mediate primates’ social decision making. This thesis investigates each of these hypotheses. Personality was assessed in 127 capuchins from 7 international sites using the Hominoid Personality Questionnaire, and then validated at Living Links (LL) using behavioural codings; this was the first-ever description of personality structure in brown capuchins. Brown capuchins have five personality dimensions: Assertiveness, Openness, Sociability, Neuroticism, and Attentiveness. Ratings were consistent across observers, and predicted relevant behaviours among the LL capuchins over a year later (e.g. scores on Sociability predicted time spent in close proximity to others). “Social success” in the LL capuchins was assessed in terms of centrality in spatial proximity networks. Individual scores on social network centrality were significantly correlated with scores derived from a Principal Components Analysis of eight affiliative and agonistic behaviours among the LL capuchins, indicating that spatial proximity is a reliable measure of the quality of subjects’ social embeddedness within their groups. Social rank and two personality traits (Assertiveness and Sociability) were positively related to network centrality, while another personality trait (Neuroticism) was negatively related to centrality. Sociability was a significant predictor of network centrality even after controlling for social rank and the other personality traits, highlighting the importance of this personality trait in shaping the social success of capuchins beyond that of basic social rules (e.g. kinship, sex, and rank). Individual learning was assessed in the LL capuchins by administering two operant tasks to subjects under conditions of free choice participation. In Task 1, thirteen monkeys participated, and eight individuals met learning criteria (i.e. >80% trials correct over 3 consecutive sessions). In Task 2, fifteen monkeys participated, and five individuals met learning criteria; the monkeys that learned this second task were also among those individuals that learned Task 1. For monkeys that regularly participated in both tasks (i.e. >50% of sessions), their average performances (i.e. % trials correct) were significantly correlated with individual scores on Assertiveness, but not the other four personality traits, or individual differences in attention span during testing, the percent of sessions subjects participated during testing, the amount of scrounging events subjects directed towards others within their social group, or the percent of observation time subjects spent feeding within their main indoor/outdoor enclosures. In terms of social success, relatively better learners had lower social rank and network centrality compared to relatively poor learners. Also, compared to poorer learners, better learners were generally less likely to direct affiliative acts (e.g. grooming, food sharing, coalitionary support) to other group members. Controlling for Assertiveness (i.e. the only variable related to individual differences in subjects’ average learning performance), individual differences in learning performance were no longer significantly related to social rank, network centrality, or the amount of affiliative acts subjects initiated with others. Collectively, such findings contrast the hypothesis that better learners should (concurrently) be more socially successful than poorer learners, and instead are more reflective of hypotheses pertaining to behavioural innovation and/or the study of individual differences. Social rank and certain traits of personality (Assertiveness, Openness, Neuroticism, and Sociability) appear to interact with capuchins’ patterns of social interaction, and one personality trait (Assertiveness) may mediate how individual differences in learning are associated with differences in social success.

The common marmoset is the most frequently used New World primate in laboratory research and testing. In the UK, their use is strictly controlled by the Animals (Scientific Procedures) Act, which is underpinned by the principles of humane science: Replacement, Reduction and Refinement. Despite their use, there are a number of problems associated with the breeding of marmosets, including low dam longevity and increasing litter sizes. Large litters have led to high infant mortality and the need for human intervention to improve infant survival, which involves removal from the family for substantial periods of time. Previous research in a range of primate species shows that early life family separation is associated with numerous adverse behavioural and physiological effects. This project therefore sought to systematically investigate the effects of breeding and infant rearing practices, integrating a number of measures to assess the welfare of laboratory- housed marmosets. Potential predictors of dam longevity and litter size were first identified in three captive UK colonies, over four decades. Dam longevity was found to be approximately 6 years, with heavier dams living longer, but overall there was no consistent improvement in longevity over the decades. As longevity varied widely between colonies and over time, environment may be one of the most important factors. Approximately half of all births at each colony were litters larger than two, and these larger litters had greater infant mortality. Only dam weight at conception was useful in predicting litter size, with heavier dams producing larger litters. The consequences of large litters and early separation from the family for supplementary feeding were then investigated. Although twins had lower body weight than 2stays (two infants remaining with the family after death of the other littermate/s) and supplementary fed triplets, they also had the fewest health problems. There was also some evidence that animals from larger litters were more at risk of suffering from extreme low weight. Some minor differences were found in behavioural development between litter sizes. Singleton infants received more rejective rearing, while 2stays received more protective rearing, perhaps following the loss of an infant. While twin infants gained independence earlier than singletons or 2stays, they did not appear to cope better with stress in adulthood, displaying more significant increases in stress-related behaviour following the routine stressor of capture and weighing, compared to 2stays and supplementary fed triplets. While overall cortisol unexpectedly decreased from baseline to post capture, there were only significant fluctuations in 2stay marmosets. Instead, there were some increases in positive behaviour in supplementary fed triplets following the stressor, suggesting enhanced coping ability. However, in another group of supplementary fed triplets, there were subtle increases in depressive-like symptoms, measured using cognitive bias and preference tests, suggesting a reduced expectation of and interest in rewards. There were however no differences between family-reared and supplementary fed marmosets in time to learn a visual discrimination task, or in responses to temperament tests. Therefore, while it was hypothesised that early family separation would have adverse developmental consequences, there were actually very little differences between marmosets of different litter sizes and rearing backgrounds, across the range of measures. Results suggest that the current supplementary feeding programme, along with a regular human socialisation programme, minimises any potential negative effects. However, we should always be finding ways to improve the lives of animals in our care. Possible Refinements include reducing dam weight to increase twin births and improve infant survival, and training to allow supplementary feeding on the carrier’s back, to prevent infant separation and reduce disruption to the family. These Refinements could reduce fear and allow monkeys to become more resilient to the laboratory environment.

Titi monkeys have long been known for their complex vocal behaviour with numerous high- and low-pitched calls, which can be uttered singly or combined in more complex structures. However, up to date very little is known concerning the function, meaning and context-specific use of these vocal utterances, and virtually nothing is known about their vocalisations in the predation context. This thesis presents a detailed description of the form and function of the anti-predator behaviour of one species of titi monkeys, the black-fronted titi monkey (Callicebus nigrifrons), with a specific focus on their alarm call behaviour. A second aim was to determine the exact mechanisms of alarm calling behaviour, with an emphasis on production and comprehension. Data were collected from several habituated groups in the Caraça Reserve, Minas Gerais, Brazil. Results showed that, when detecting predator species, C nigrifrons produce sequences that initially contain two types of brief, high-pitched calls with distinct frequency contours. Further evidence suggested that some of these sequences are meaningful to conspecific receivers, by indicating the general predator class and location of threat. There were also indications that, within the terrestrial threats, additional information may be encoded by acoustic and compositional differences. Analyses of call order and number of calls per sequence suggested that callers may be able to convey information on both predator type and location. The black-fronted titi monkeys’ vocal system thus provides a further example of zoo-syntax, in which acoustically fixed units of a vocal repertoire are combined into higher order sequences that are meaningful to recipients. According to current definitions, this type of calling behaviour qualifies as functionally referential, by indicating general predator class, terrestrial predator type and location. As such, this is the first empirical demonstration of a sequence-based alarm call system that conveys information on both predator category and location.

Comment humains et chimpanzés définissent et brouillent les frontières entre leurs espèces lors de leurs interactions ? Tel sera le leitmotiv de notre étho-ethnographie, à l’intersection de l’anthropologie sociale, des études des sciences, et de la primatologie. Au fondement de cette recherche se trouve un travail de terrain de longue durée mené dans un laboratoire de sciences cognitives situé au Japon, au sein duquel sont enseignées aux chimpanzés des compétences langagières dans le but de caractériser leur monde perceptuel. Cependant, au cœur même du contexte ce laboratoire, la nature des relations entre humains et chimpanzés est un aspect crucial de ce programme de recherche ; les deux espèces y forment une communauté hybride faite d’affects, de relations sociales et de collaboration scientifique. Afin de fournir une étude comparative, nous avons également mené une série d’ethnographies plus brèves – sur le modèle de la méthodologie multi-site – en observant cette même problématique à l’œuvre au sein de diverses institutions au Japon - zoo, sanctuaires et réserves - ainsi qu’au sein de la station japonaise pour l’étude de la culture des chimpanzés qui se trouve à Bossou, en République de Guinée. En outre, ce travail narre l’expérience que nous avons faite de devenir expérimentatrice au sein du laboratoire étudié. Le résultat en est multiple. Nous commencerons par explorer l’histoire des études sur les chimpanzés menées à l’Institut de Recherche sur les Primates de l’Université de Kyoto (KUPRI) ainsi que les pratiques de soin et de recherche qui s’y sont mises en place. Ensuite, nous étudierons les dynamiques qui caractérisent (1) les frontières physiques, lors d’interactions sociales entre deux espèces qui peuvent s’avérer dangereuses, (2) les frontières expérimentales, lorsque le chimpanzé n’est pas seulement celui qui fait l’objet d’une expérience mais qui met également à l’épreuve son expérimentateur, (3) et les frontières symboliques, lorsqu’est interrogée la définition de la « personne » humaine et non humaine. Ainsi, quatre points principaux sont examinés à nouveaux frais, en particulier (a) la socialisation interspécifique (b) l’incarnation des relations inter-espèces dans un espace donné (c) les relations inter-espèces dans un contexte scientifique (d) l’examen de perspectives zoocentrées sur la « personne ». Nous conclurons avec l’évocation de nos espoirs et de nos attentes quant à un dialogue fructueux entre les différentes disciplines en jeu. L’apport de ce travail consistera en effet à mobiliser des concepts et des outils de la primatologie et des sciences sociales afin de proposer une analyse plus symétrique des relations entre humains et animaux. / How do humans and chimpanzees set and blur boundaries between species when interacting with each other? This is the leitmotif of this etho-ethnography at the intersection of social anthropology, social studies of science and primatology. This endeavor is based on long-term fieldwork conducted in a cognitive sciences laboratory in Japan, which teaches chimpanzees language-like skills as means to understand their perceptual world. However, in this laboratory setting, the human-chimpanzee relationship is a vital part of the research philosophy and both species constitute a hybrid community of affections, social relationships, and scientific partnering. As a comparative effort, a short-term multi-sited ethnography was conducted following the theme across institutions in Japan of zoo, sanctuary and field-site type, in addition to the Japanese field station for the study of chimpanzee culture, in Bossou, Africa. Moreover, this work draws on the experience of becoming, at the same time, an experimenter in the targeted laboratory. The result is multifold. We shall explore first, the history as well as the caretaking and research practices in chimpanzee studies at the Primate Research Institute of Kyoto University (KUPRI). Then, we shall investigate the dynamics of physical boundaries in dangerous interspecies social interactions; the experimental boundaries of testing and being tested by chimpanzees; and the symbolic boundaries concerning human and nonhuman personhood. As a result, four major points are brought to light in a renewed perspective, namely (a) interspecies socialization (b) the embodiment of interspecies social relations in space (c) interspecies social relations in scientific settings (d) animalcentric perspectives on personhood. We conclude with the hopes and prospects for a fruitful dialogue across disciplines. Overall, the differential endeavor of this work consists in mobilizing concepts and tools from both primatology and social sciences to propose a more symmetric analysis of the human-animal relationship.