Individual differences in the sexual behaviour of male rhesus monkeys (Macaca mulatta) under laboratory conditions

Sexual behaviour was studied quantitatively in eight male and seven female adult rhesus monkeys, paired in sixteen oppositely-sexed combinations, during regular test sessions conducted over a period of 13 months. Results indicated that the overall level of sexual interaction of pairs was determined largely by the male partner. The range of variation between males was large across all the indices of sexual behaviour used. Highly significant differences were found in the indices of behaviour of different males tested with the same group of females, whereas differences were smaller when different females were tested with a single male, indicating the predominant role of the latter. Paired tests showed that the menstrual cycle of the female did not influence the differences in the behaviour of males. Successive ejaculations in a test resulted in a progressive decline in sexual performance and an increase in refractory periods. The relevance of these findings for the design of experiments concerned with the control of mating behaviour in the rhesus monkey is discussed.