Steroid hormone influences on the mating behavior of vervet monkeys (Cercopithecus aethiops)

Eight ovariectomized female vervet monkeys (Cercopithecus aethiops) were tested in heterosexual and isosexual pairs, under estradiol and testosterone treatments. Pairs were tested under two different experimental situations in which the male was either restrained or left free. There were only small behavioral changes across the treatments, involving mainly male responses. Erection time, frequency of intromission, ejaculation, and olfactory investigation increased during estradiol treatment whereas during administration of testosterone erection time, the number of approaches, contacts, and olfactory investigations decreased. Female behaviors were relatively independent of hormone treatment showing only the disappearance of negative responses with estradiol and an increase of yawns with testosterone. Female behaviors were performed at a higher level with male partners than with other females, and the frequencies of spontaneous presents varied with the sex of partner. It is suggested that in vervet monkeys both estradiol and testosterone affect female attractivity, estradiol further influences receptivity, whereas proceptivity appears to be less directly involved in sexual interactions and more related to social context.