No abstract

In nonhuman animals, individuals of the same sex and age differ in their behavior patterns consistently across time, comparable with human personality differences. To draw conclusions about the adaptive value of behavior traits, it is essential to study them in the wild where animals are subject to the ecological pressures that promoted the evolution of behavior strategies. This study was conducted in the Phu Khieo Wildlife Sanctuary, Thailand, on 4 groups of habituated wild Assamese macaques by observers who had familiarized themselves with the subjects over the course of an ongoing long-term study. We used a multimethod approach enabling the most comprehensive understanding of variation in stable interindividual differences in a species-typical ecological setting. We combined trait ratings (TRs), assessed with observer-report questionnaires (54-item Hominoid Personality Questionnaire) of 107 individuals of diverse age-sex classes, with behavior codings (BCs) of 24 adult males. We found male and female personality constructs to be congruent and examined reliability and construct validity. Combining trait rating and behavioral coding, we found two solutions with five factors to best describe the personality structure of the males: one structure comprised the dimensions Gregariousness BC , Aggressiveness BC , Sociability BC

23Animal social bonds are defined as stable, equitable and strong affiliative and cooperative 24 relationships similar to human friendships. Just as human friendships, social bonds are 25 thought to function as alliances that generate adaptive benefits via support in critical 26 situations. In humans, similarity in many sociodemographic, behavioural and intrapersonal 27 characteristics leads to trust and is predictive of friendships. Specifically, personality 28 homophily, that is the tendency of individuals to form social bonds with others who have a 29 similar personality, may increase predictability and facilitate trust and reciprocity among 30 partners with compatible behavioural tendencies. While evidence for social bonding in 31 nonhumans is accumulating, far less is known about its predictors. Here, personality 32 homophily effects on the formation and maintenance of social bonds are shown in twenty-four 33 wild male Assamese macaques (Macaca assamensis), at Phu Khieo Wildlife Sanctuary, 34 Thailand. Dyadic bond strength increased with increased similarity in the trait Connectedness 35 (i.e. frequent and diverse neighbours in 5m proximity and pronounced social tolerance, as 36 high rates of friendly approaches to and by others). To differentiate whether homophily 37 indeed predicted bond formation or whether bonded males' personalities became more similar 38 over time, we tested the stability of the connectedness traits in a subset of immigrating males 39 that had to form new bonds. Connectedness in these males remained stable suggesting that 40 males do not adapt their personality to their partner. Our results support the idea of a shared 41 evolutionary origin of homophily as a partner choice strategy in human and non-human 42 animals. The main selective advantage of personality similarity in animal social bonds may 43 result from a more reliable cooperation among individuals with similar cooperative 44 behavioural tendencies.45