Influence of estrogen-treated females on sexual behavior and male testosterone levels of a social group of rhesus monkeys during the nonbreeding season.

The effect of the sequential estradiol benzoate treatment of each of 6 ovariectomized (OVX) females on a social group of rhesus monkeys was examined during the period from May to August. The group was housed outdoors and was composed of 7 adult males and 5 intact females, in addition to the 6 OVX animals. Social behavior was observed and male testosterone levels were monitored before, during and after estrogen treatment of the OVX females. Behavior of an unmanipulated group was also examined, and no sexual behavior occurred in this control group from May through August. In contrast, the sexual behavior of both males and gonadally intact females of the experimental group increased when estrogen-treated females were present. Sexual behavior remained elevated after the estrogen-treated females had been removed and continued so into the breeding season. The sexual behavior of the untreated females was displayed in cycles about 26 days in length. Male testosterone levels increased to values typical of the breeding season. Aggressive and submissive behavior also increased during the treatment. These results confirm previous findings about the influence of estrogen-treated females on male sexual behavior, and present the first direct evidence of increased testosterone levels in this situation. In addition, the data suggest that the presence of estrogen-treated females can induce sexual behavior in the other females of the same social group.