Abstract
This study outlines environmental and internal factors affecting the seasonal breeding of Japanese monkeys (Macaca fuscata). 1) Females housed indoors exhibited the prolonged breeding season as well as the reduced inhibition of ovarian functions during the nonbreeding season in comparison with those housed out-doors, as judged from reproductive endocrine profiles. 2) Artificial manipulation of photoperiod alone had no effect on the manifestation of annual reproductive cyclicity, whereas simultaneous manipulation of photoperiod and ambient temperature was at least to some extent effective in modifying the ovarian functions. 3) Estradiol-treated ovariectomized monkeys exhibited marked seasonal changes in response to the negative feedback action of estradiol on LH secretion. 4) Thyroidectomy resulted in significantly earlier termination of the breeding sea-son. 5) Analysis of hormonal profiles in socially housed male and female monkeys revealed that onset of the breeding season was preceded by the increase in plasma testosterone and inhibin in male monkeys, which sug-gested that social factor is also involved in the manifestation of the breeding seasonality. From these studies, it is concluded that seasonal breeding of Japanese monkeys is governed by biannual changes in the response of the hypothalamo-hypophysial axis to the negative feedback action of estradiol, and that multiple annually cyclic environmental factors appears to influence the seasonal breeding of this animal.
