Hormonal contraceptive affects heterosexual but not homosexual behavior in free-ranging female Japanese macaques over 17 mating seasons

We assessed the effect of a progestin-based contraceptive treatment (chlormadinone acetate) on female heterosexual and homosexual behaviors in a free-ranging group of Japanese macaques (Macaca fuscata) living at Arashiyama-Kyoto, Central Japan. The data included estimated intensity of fertility cues, sexual solicitations and mounting behaviors collected daily during 17 consecutive mating seasons (1995-2012) from 159 females. Females that were on contraception: (1) exhibited less intense cues of putative fertility and for shorter periods; (2) were solicited by fewer males, and those males that did solicit them did so less often (i.e., lower heterosexual attractivity); (3) solicited fewer males and when they did perform sexual solicitations they did so less often (i.e., lower heterosexual proceptivity); (4) engaged in shorter heterosexual consortships with fewer male partners (i.e., lower heterosexual receptivity), compared with females that were not on contraception. In contrast, contraceptive treatment had no significant effect on the prevalence, occurrence, frequency, or duration of female homosexual behaviors. Even though heterosexual and homosexual behaviors can both be considered sexual in character and under hormonal control, our results suggested they are, to some extent, dissociable. Because females engaging in homosexual interactions showed less intense cues of putative fertility than those engaging in heterosexual interactions, regardless of contraceptive treatment, we argued that the hormonal threshold required for the expression of heterosexual behavior by females was associated with elevated sex hormones levels compared to homosexual behavior. We discussed the hormonal correlates of sexual behavior and partner preferences in Japanese macaques.