The role of kinship in the formation of a primate multilevel society.

A small number of mammalian species live in a modular or multilevel society in which several individual social/reproductive units called one-male units (OMUs) are embedded within a large cohesive band. Factors that affect band composition and stability are poorly understood. In this study we examined the role of kinship in the formation and maintenance of a multilevel society in an endangered population of golden snub-nosed monkeys (Rhinopithecus roxellana). From 2005 to 2011, we obtained genetic samples from 86 individuals (including 88.9% of leader males and 80.5% of adult females) living in a band of 8-10 OMUs. We used microsatellite genotyping to identify patterns of relatedness and individual transfer. We found that adult females residing in the same OMU were more closely related to each other than to a random set of females drawn from the band and that females tended to disperse into OMUs that contained female relatives. In addition, adult females who transferred were not more closely related to their previous leader male than to the leader male of their new OMU. These results support the contention that kin bonds contribute importantly to the formation and stability of this primate multilevel society by influencing a female's decision to remain in her current OMU, or during transfer, which new OMU to enter.