Sex differences in use of a species-typical facial gesture by pigtail monkeys (Macaca nemestrina)

Abstract

A species-typical gesture, the “jaw thrust”, was sequentially analyzed in a group of adultM. nemestrina. The major finding was a sex difference in apparent function with male jaw thrust sequences most likely to result in sexual behavior and female sequences most likely to terminate in agonistic behavior. Sex differences in the initiation and reception of jaw thrusts were also observed; they were most commonly initiated by males and directed toward females. Marked stereotypy of the behavioral sequences including jaw thrusts was observed: only a small proportion of the species’ behavioral repertoire was exhibited in temporal association with the gesture. Despite the striking nature of the gesture and the frequency with which it was exhibited, a majority of the signals had no overt social effect.