Sexual arousal in male pigtailed monkeys (Macaca nemestrina): effects of serial matings by two males.

Male sexual arousal was examined in pigtailed monkeys (Macaca nemestrina), with the postejaculatory interval (PEI) used as the dependent variable. In male-female pairs, the PEI is shortened by 60% of normal (control) values if the male observes another male copulating with his female partner. This result demonstrates that the normal PEI is not an absolute male refractory period; males are capable of copulating sooner, and they will do so when presented with certain behavioral stimuli. A possible functional interpretation of the result with regard to male reproductive competition is presented.