Personality, Social Behavior, and the Maintenance of Cohesion in a Multilevel-Society Primate (Rhinopithecus roxellana)

Understanding how individual personality traits impact social interactions and cohesion in complex animal societies remains a critical challenge, particularly in wild populations of nonhuman primates. This study investigated personality in a free-ranging population of golden snub-nosed monkeys (Rhinopithecus roxellana), a high-altitude temperate forest species organized in a multilevel social system. Personality structure was quantified using the Hominoid Personality Questionnaire, and its relationship to group cohesion was assessed through 12 behavioral variables and female transfer status. A behavioral experiment was designed to evaluate the tendency of individuals to temporarily depart from collective movement. Factor analysis of 41 questionnaire items revealed four distinct personality dimensions—Assertiveness, Openness, Neuroticism, and Sociability—that accounted for substantial inter-individual variation. Personality scores varied significantly by sex and dominance rank: males exhibited higher Assertiveness, females exhibited higher Sociability, and Neuroticism was negatively associated with dominance rank. Personality traits were linked to cohesion-related behavior, with Assertiveness positively associated with both affiliative and aggressive interactions, and Sociability predicting higher grooming rates. Moreover, Sociability and Openness showed opposing but insignificant influences on female transfer, with Openness additionally associated with temporary separations, suggesting that personality shapes both intra-unit cohesion and inter-unit fluidity in multilevel societies. These findings demonstrate that personality is a determinant of social organization and dynamics in primates, providing new insights into the evolutionary processes that influence and maintain complex social systems.