Female dominance rank and behavior during artificial menstrual cycles in social groups of rhesus monkeys (Macaca mulatta).

We recently reported (Michael & Zumpe: American Journal of Primatology 15:157-170, 1988) evidence for the hypothesis that copulations by pairs of rhesus monkeys are linked more closely to the ovulatory phase of the female's menstrual cycle when a male has access to several females in different cycle phases rather than access to females in the same cycle phase. We have now used data from this earlier study to assess the role of female dominance. Artificial menstrual cycles were induced with hormone injections in two of four ovariectomized females in eight social groups (each consisting of one male and four females). The artificial cycles were either synchronized or offset by 7-day increments. There were differences in the behavioral interactions of the higher-ranking (dominant) and lower-ranking (subordinate) hormone-treated females in each group. The amount of male sexual activity received by dominant and subordinate females differed little, but dominant females initiated significantly more sexual activity (P<.0001) than did subordinate females. Dominant females were significantly more aggressive (P<.0001) toward other females and received more direct and redirected aggression from males. Males generally initiated and maintained more social contacts with dominant than with subordinate females, and dominant females were less active than subordinates in initiating and maintaining social interactions with males. The findings provide new evidence for both female mate competition and mate choice by males for higher-ranking females.