Opposite-sex social bonding in wild Assamese macaques

In large multimale-multifemale primate groups, individual adult males and females may form close social relationships that extend beyond the mating context, a surprising finding for polygynandrous mammals. The patterns of these associations can be relatively stable across time. Here we investigate whether dyadic social relationships between the sexes transcend mere association in wild Assamese macaques and may be characterized as strong, equitable, and stable affiliative relationships or social bonds. We collected >9,000 hr of focal animal data on adult males and females from two groups of wild Assamese macaques (Macaca assamensis) at Phu Khieo Wildlife Sanctuary, Thailand. Using dyadic composite sociality indices, we found male-female affiliative relationships to be highly differentiated. The stronger the relationships were, the more likely partners were to reciprocate grooming and the more stable were the relationships. In addition, the strongest dyadic relationships remained stable over multiple years as long as both partners remained in the group. These results indicate that in a polygynous species particular males and females form strong, equitable, and enduring affiliative relationships qualitatively similar to the same-sex bonds described for female baboons and male chimpanzees. Am. J. Primatol. 78:872-882, 2016. © 2016 Wiley Periodicals, Inc.