Sexual preferences during artificial menstrual cycles in social groups of rhesus monkeys (Macaca mulatta)

Abstract

Eight groups of rhesus monkeys each consisting of one male and four ovariectomized females were observed while two of the females were treated with hormones to produce artificial menstrual cycles. These were either synchronized or offset by 7-day increments. Sexually preferred females, defined by the numbers of ejaculations per test, received almost twice as many ejaculations as did non-preferred females during all synchronized and offset cycles and during all cycle phases. However, short-term changes in partner preference occurred when the midcycle phase of non-preferred females coincided with the middle or late progesterone phase of preferred females, suggesting a negative effect of progesterone on behavior during the menstrual cycle. There were highly significant differences between preferred and non-preferred partners for almost all of their sexual and social interactions, and preferred partners showed longer proximity and grooming times as well as higher levels of sexual activity. Partner preferences accounted for more of the behavioral variance between pairs than did female dominance, although males sought the proximity of dominant females independently of their partner preferences. Thus, in a setting uncomplicated by male mate competition, sexual preference by male rhesus monkeys is a robust phenomenon depending on complex interactions between dominance, hormonal status, and the individual behavior of female partners.