Female Mounting in Japanese Macaques: Proximate and Ultimate Perspectives on Non-conceptive Sex

It is hypothesized that female-male mounting is an adaptive behaviour, functioning to prompt sluggish males to mount females in return. This hypothesis has been proposed many times and independently by different authors, however it had yet to be tested. Furthermore, the proximate mechanisms that drive the behaviour, specifically the male and female movements and actions that prompt its occurrence, are relatively unknown, having only been reported in an anecdotal sense. In this chapter, I investigated both the adaptive function and proximate mechanisms that drive female-male mounting. In accordance with the “proceptivity hypothesis”, I predicted that female-male mounting should be related to both an increase likelihood of occurrence and an increased frequency of subsequent male-female mounting, As for proximate mechanisms, I found that females were the initiators of female-male mounting during 79% of observed mounts. Furthermore, males were found to rise to be mounted in response to both ambiguous cues (i.e. females moving their bodies to position themselves into the mounter position) and explicit signals (i.e. females grasping the males’ hindquarters) emitted by females initiating and carrying out the female-male mounting process. These results suggest that males anticipate and facilitate female-male mounting.