Sexual maturation and seasonal changes in reproductive phenomena of male Japanese monkeys (Macaca fuscata) at Takasakiyama

Abstract

ABSTRACT. The authors examined testis tissues and blood which were collected from free-ranging Japanese monkeys of the Takasakiyama troop during four periods in 1971 (mating season: late January-early February; early birth season: June; late birth season: August; and intermediate season between birth season and mating season: October), and studied their sexual maturation and seasonal changes in reproductive phenomena.Results of observations on the testis and plasma testosterone concentration were in agreement with each other. Except in a few cases, the testis was infantile until October at 4 years old and developed rapidly during the following two months, and spermatogenesis started in the mating season at 4 years old (in exceptional cases, it started one year earlier). After the following two-year process of sexual maturation, monkeys attained full maturation in the mating season at 6 years old.For seasonal changes in reproductive phenomena also, results of observations on the testis and the plasma testosterone were in agreement with each other. Activity of the testis repeated an annual cycle of being maximal in the mating season, regressing in the birth season, and redeveloping toward the following mating season. Such seasonal changes were noticeably observed with 4-to 6-year-old animals, which are in the process of sexual maturation.

The Influence of Rearing Conditions on the Physical Growth of Captive Japanese Macaques (Macaca fuscata).

“…The timing of major physiological growth events, such as weaning and sexual maturation, were the same for the two groups, and similar to those reported previously in Japanese macaques [8,[10][11][12]. Trends of growth in the Enclosure group macaques were similar to those of free-ranging Japanese macaques [3,4].…”

Time Series Analysis of Plasma Insulin-like Growth Factor-I and Gonadal Steroids in Adolescent lapanese Macaques (Macaca fuscata).

“…As Japanese macaques are strictly seasonal breeders [18][19][20][21][22], seasonal changes in hormone secretion would be superimposed on the agedependent changes. The present study, therefore, attempted to obtain seasonal and age-dependent components from the hormonal and body weight changes around the adolescent period.…”

“…This reproductive seasonality would presumably affect the timing of sexual maturation [20] as well as body growth. Our previous study on the morphological growth of the Japanese macaque by the long-term longitudinal method demonstrated that its adolescent growth is characterized by slowness and late start, resulting from adaptation to highly seasonal environment in a temperate zone [23].…”

“…Japanese macaques are distinguished from other members of the fascicularis group of the Genus Macaca [17] by their clear breeding season from autumn to winter [18][19][20][21][22]. This reproductive seasonality would presumably affect the timing of sexual maturation [20] as well as body growth.…”

Preliminary Report on Histological Characteristics of Male Reproductive Organs in Senile Japanese Macaques

“…The process of sexual maturation has been well studied, especially in Japanese macaques (Nigi, 1975;Nigi et al, 1980;Matsubayashi and Mochizuki, 1982). There are many reports on the histological structure of the male reproductive organ as well as their seasonal changes (Kinzey, 1971;Glick, 1979).…”