OVARIAN HORMONES AND GROOMING BEHAVIOUR IN THE RHESUS MONKEY (MACACA MULATTA) UNDER LABORATORY CONDITIONS

Abstract

SUMMARY: Grooming behaviour was studied quantitatively by observing pairs of oppositely sexed, adult rhesus monkeys during regular hourly test sessions over 2 yr.; at all other times the animals were caged singly. Rhythmic fluctuations in both male and female grooming occurred in relation to the menstrual cycle; the grooming times of males reached a maximum near mid-cycle, at which time the females' grooming was at a minimum. In some pairs, there were additional changes in the grooming times immediately before menstruation in the same direction as those near mid-cycle. Bilateral ovariectomy of the female of the pair abolished all rhythmic variations and reduced the grooming of the males. Subcutaneous injections of oestradiol into the ovariectomized female restored the grooming of males to the levels seen near mid-cycle. The subsequent addition of progesterone partially, but always consistently, antagonized the effects of oestradiol. Analysis of the hormone-induced alterations in grooming behaviour indicates a primary influence on the effectiveness of the grooming invitations of females, the proportion accepted by males increasing with oestradiol administration. These findings indicate that endocrine factors play a role in regulating grooming activity which constitutes an important aspect of the social behaviour of primates.