Male-female and female-female mounting in Japanese macaques: A comparative study of posture and movement

Mounting is generally considered to be a male-typical behavior. Female Japanese macaques, in certain populations, are unusual, in that they routinely mount other females. In this study, we examined to what extent female Japanese macaques mount same-sex partners in a male-typical manner. We compared the mount postures males and females adopt and their rate of pelvic thrusting. In addition, we employed a modified form of Laban Movement Analysis (LMA) to compare patterns of pelvic movement during mounts. LMA is a universal language for movement that describes quantitative features of movement, such as changes in the relation of the body segments, as well as qualitative features, such as the style of movements. Our results indicate that female Japanese macaques do not mount in a male-typical manner. Females exhibited a much greater variety of mount postures than did males. Some of the most common types of mount postures employed by females were never exhibited by males. Females performed fewer pelvic thrusts per mount than males, but they executed more pelvic movements per mount, as well as, greater variety and complexity of movement. In addition, the qualitative style of pelvic mounting that females employed differed, in general, from that of males. We argue that these sex differences in mounting can be explained by the fact that both sexes sought sexual reward via genital stimulation during mounting, but they did so in different ways owing to the constraints imposed by their genital architecture. This study raises the larger question as to what constitutes a male-typical or female-typical behavior.