Abstract
Feral raccoons (Procyon lotor) have been increasing in number since 1979 and are currently under pest control in Hokkaido. One of the reasons for the increase in numbers is thought to be the high reproductive potential of raccoons, but little is known about their reproduction. The main aim of this study is to clarify seasonal changes in spermatogenesis and peripheral testosterone concentration of raccoons in Hokkaido. In the present study, external characteristics and histology of the testis and epididymis, and plasma testosterone concentration were investigated in 68 feral, male raccoons culled for pest control and once a month in one live, captive male. The feral males exhibited seasonal changes in spermatogenesis, which indicated active in autumn, winter, and spring (October–June) with noted spermatogenesis, and inactive in summer (July–September) with lower mean levels of presence of spermatozoa in the cauda epididymis. Even in the inactive period, spermatozoa were observed in about half of the individuals (14/26), therefore individuals producing spermatozoa existed every month throughout the year. Testosterone concentrations were significantly high in winter mating season. In the captive male, testosterone concentrations were low from June to August, and spermatozoa could not be observed from July to September. These results suggest that raccoons exhibit seasonality of reproduction, but the time and duration of spermatogenetic decline varies widely among individuals. This individual variation in the inactive period is a feature of male raccoon reproduction unique among seasonally breeding mammals.
