Ventro-Ventral Copulation by an Adult Male-Female Pair of Japanese Macaques at Arashiyama

Abstract

Ventro-ventral (VV) mountings during copulation are most dominant in humans. In contrast, nonhuman primates have a strong bias toward dorso-ventral mountings, and only apes have been known to show VV mountings during copulation between a pair of mature individuals. Reporting VV mountings during copulation in primates other than apes is critical to discussions regarding why VV mountings have been limited to apes among primates. Here, I report VV mounting in a mature male and female pair of provisioned Japanese macaques (Macaca fuscata). This is the first report of VV mountings during copulation by adult nonhuman primates without disabilities other than apes. The pair of monkeys performed VV mountings 13 times over a week. Following the mounting series, including VV mountings, the presence of a copulatory plug was confirmed around the female’s vagina, indicating that the VV mountings were part of their copulatory behaviors. The male initiated all VV mountings, and the female was often uncooperative during these attempts. In all cases, the female was lying on her back, and the male was on top. The pair were in close contact and did not see each other’s faces during VV mountings. This report suggests that eye contact between mates and morphological characteristics are the primary reasons for the evolution of VV mountings during copulation in apes.