Annual Reproductive Patterns of Male House Shrews, Suncus murinus, in Central Taiwan

The reproductive patterns of male house shrews, Suncus murinus, inhabiting Taichung, Taiwan, were investigated September 1990-February 1992 with animals collected monthly. The annual average body weight and testis weight were 58.6 g and 87.0 mg, respectively, for adults (n = 183) and 32.9 g and 47.2 mg, respectively, for juveniles (n = 19). Levels of androgen in plasma of adult males were highest during March (882.9 pg/ml) through August (714.5 pg/ml), and then decreased gradually to 357.5 pg/ml in February. Histological examination of testes revealed that spermatogenesis occurred year round with maximal activity and intensity during March–August. Males in reproductive condition were present year round with the greatest number in July–August and the lowest in December–February, according to their spermatogenic activity. Levels of androgen in plasma were correlated with spermatogenic activity and growth of the seminal vesicle-prostate. Body weight, testis weight, weights of epididymis and seminal vesicle-prostate, and level of androgen in plasma were correlated with length of day, temperature, and rainfall. Our study demonstrated that male Suncus murinus in central Taiwan is a continuous breeder with greater reproductive activity and intensity during spring and summer. This is the only study to investigate seasonal or monthly patterns of androgens in plasma of wild S. murinus and is the first to demonstrate that sexual maturation and development in wild populations are correlated with photoperiod and other environmental factors.