Effects of the presence of a second male on pair-tests of captive cynomolgus monkeys (Macaca fascicularis): Role of dominance.

Abstract

In social macaques, sexual, aggressive and social interactions between a male and female occur in a complex setting in which the presence of other members of the group may exert powerful, long-lasting effects. We have studied the effects of the presence of a second male, either immediately before or during pair tests, on the behavioral interactions of male cynomolgus monkeys with their female partners. Twenty-minute tests were conducted in a large room containing a small compartment that confined a second male. Each of 8 males served in turn both as a test male and as a second male (stimulus male)(4 females, 8 male-female pairs, 480 pair-tests). After 5 weeks of pair-testing with a stimulus male absent to establish behavioral baselines, the test conditions were changed daily during the next 5-week period in the following way: (1) pair-test immediately after the test male was observed with the stimulus male (Mondays), (2) control pair-test (Tuesdays), (3) pair-test in the presence of the stimulus male (Wednesdays), and (4) control pair-test (Thursdays). A final 5-week control period of pair-testing followed with the stimulus male absent. Stimulation of a test male by a second male either immediately before or during the pair-test had highly significant but different effects. Ejaculatory activity increased in tests that followed stimulation, mainly in males dominant to the stimulus male, while sexual and social activity decreased in tests during stimulation, but mainly in males subordinate to the stimulus male. The findings suggested that dominance confers a mating advantage on males even when there is no opportunity for mating interference or active mate competition.