A review of sexual initiating behavior by male and female cynomolgus monkeys and some species comparisons

Abstract

The sexual initiating behavior of male and female cynomolgus monkeys (Macaca fascicularis) observed during standard laboratory tests is reviewed and compared with that of rhesus monkeys (M. mulatta) observed under identical conditions. Species differences in sexual behavior are related here to differences in habitat, sexual dimorphism, and the dominance gradient between the sexes. Compared with rhesus monkeys, cynomolgus monkeys appear to be more arboreal, less sexually dimorphic, and have a smaller dominance gradient between the sexes. They exhibit a facultative single-mount copulatory pattern rather than the serial mount pattern of the rhesus monkey. Female cynomolgus monkeys are less dominated than rhesus females by their male partners. Direct aggression between mates is more frequent and redirected aggression occurs less often than in rhesus monkeys. These behavioral differences affect the interpretation of changes in initiation rates that occur (1) during the menstrual cycle, (2) when females are ovariectomized and given hormone replacement treatments, and (3) when males are castrated and treated with androgens. We conclude that estradiol in the female and testosterone in the male increase the sexual motivation of both the treated and the untreated partner. Valid interpretations of changes in initiation rates depend on accurate and exclusive definitions of behavior and on a consideration of the behavioral context in which they are made.