Comparison of genital contact behaviors among Macaca assamensis pelops in Nepal, M. a. assamensis in Thailand, and M. thibetana in China

We studied the social behaviors of western Assamese macaques (Macaca assamensis pelops) at Shivapuri Nagarjun National Park, Nepal from 2014 to 2017 and of eastern Assamese macaques (M. a. assamensis) at Wat Tham Pla, Thailand from 2008 to 2012. The behaviors of both subspecies of M. assamensis were compared to those of Tibetan macaques (M. thibetana) at Huangshan, China from 1989 to 1993. The study groups were free-ranging, provisioned daily, and habituated to observers. We observed adult males and adult females for 10 h each during both the birth and mating seasons using focal-animal sampling as well as all-occurrence-behavior sampling. All three species of macaque formed multi-male multi-female social groups with female philopatry, male dispersal, and a linear dominance hierarchy among adult females. Additionally, although they did not make genital-genital or oral-oral contact, all three species performed various affiliative behaviors with genital touching and genital showing during not only the mating season but also the birth season. However, we found more differences in the repertoire of social behaviors between western and eastern Assamese macaques than between eastern Assamese and Tibetan macaques. Bridging behavior, in which two adults simultaneously lift up an infant, was recorded in Tibetan and eastern Assamese macaques. Males of these two macaques sucked the infant's genitalia during bridging behavior and dyadic male-infant interactions, whereas this behavior was not observed in western Assamese macaques. In addition, only male Tibetan macaques directly sucked the penis of another male, although males of all three macaque species inspected female genitalia and the genital inspection was occasionally accompanied by oral-genital contact. These results indicate that bridging behavior and the sucking of an infant's genitalia by adult males evolved in a sinica species-group of the genus Macaca, particularly in the clade of Tibetan and eastern Assamese macaques, and that penis sucking between adult males occurred last in Tibetan macaques.