抄録
Reproductive physiology of Hokkaido brown bears, Ursus arctos yesoensis was studied morphologically, ethologically and endocrinologically. Age of sexual maturity was confirmed to be 24 and 14 years from the histological examination of testes and ovaries in male and female bears, respectively. Sexual behavior was observed during the breeding season to obtain data such as copulation process, changes of mating number in a day and with day and estrous duration of each female. Annual changes of serum testosterone levels, testis sizes and cell constructions in seminiferous tubules exhibited that the level of breeding function (spermatogenesis) begun to increase from February when wild bears were hibernating. It was considered that implantation occurred in late Novemberearly December and then fetuses grew as sigmoid curve by examining the change of serum progesterone levels and the ultrasonographical fetus growth. Histological examinations of ovaries and uteri and flushing in uteri resulted in finding about morphology of corpora lutea, uterine glands and embryos during the delay period. It was suggested that embryo loss, abortion and/or infant death occurred from the comparison of numbers among corpora albicantia, placental scars and litters which wild mature female bears were accompanied by.
