Female orgasm rate increases with male dominance in Japanese macaques

Under specific circumstances, nonhuman primate females may experience orgasm. The occurrence of female copulatory orgasm appears to be highly variable, however, and its proximate causation is poorly understood. We investigated the proximate mechanisms that control orgasmic response in female macaques. During 238 h of observation of sexual behaviour in a large captive group of Japanese macaques, Macaca fuscata, 240 copulations Were recorded involving 68 different heterosexual pairs formed by 16 males and 26 females. Female orgasmic responses were observed in 80 of 240 copulations (33%). The frequency of orgasms was not correlated with female age or dominance rank, but it was higher for copulations lasting longer and involving a higher number of mounts and pelvic thrusts. When the level of physical stimulation experienced by females during copulation was statistically controlled, the highest frequency of female orgasms was found among pairs formed by high-ranking males and low-ranking females and the lowest frequency among pairs formed by low-ranking males and high-ranking females. These findings suggest that the proximate mechanisms that control orgasmic threshold in female macaques are more responsive to social stimuli and less constrained by physiological limitations than previously thought. (C) 1998 The Association for the Study of Animal Behaviour