Effects of Age and Season on Sexual Behavior and Plasma Testosterone and Dihydrotestosterone Concentrations of Laboratory-Housed Male Rhesus Monkeys (Macaca mulatta)1

Abstract

Sexual behavior and plasma testosterone and dihydrotestosterone levels were examined in twelve male rhesus monkeys of different ages and at various times of the year. Plasma testosterone was found to vary significantly throughout the year. High concentrations of testosterone were measured in the fall and winter seasons, whereas low concentrations were measured in the spring and summer. A similar seasonal pattern was noted in the sexual behavior of these animals. Statistically significant reductions in the incidence of ejaculation and the frequency of yawning were recorded in the spring compared with the fall months. It appeared that changes in sexual behavior and circulating testosterone were associated.