We studied the reproductive cycle of male Chinese green tree vipers, Trimeresurus s. stejnegeri, in northern Taiwan by examining seasonal changes in the morphology and histology of their reproductive organs from May 1996 to August 1997. A total of 144 mature males was examined. Based on a histological examination of the seminiferous epithelium, we classified spermatogenesis into five stages: early recrudescence, late recrudescence, spermiogenesis, early regression, and late regression. Testis recrudescence began in the spring. Sperm started to appear in summer and roached a peak in fall. In the winter, testes of most snakes were regressed and sperm disappeared in the lumina of the seminiferous tubules. Throughout the year, sperm were present in the vas deferens. Testis mass peaked in summer, then regressed in winter and early spring. Monthly changes in seminiferous tubule diameter, seminiferous epithelium height, and fat body mass revealed a similar pattern as that of testis. These three parameters were significantly correlated with each other and with temperature and rainfall. Monthly changes in testis and fat body mass were followed by changes in kidney mass. Hypertrophy of the renal sexual segment of T. s. stejnegeri occurred from late summer to winter and might be related to mating activities observed in the sine period. As with other viperids, male Chinese green tree vipers exhibited a postnuptial spermatogenesis cycle, which may be confusing when judging from mating activities alone. We proposed another criterion to distinguish postnuptial from prenuptial spermatogenesis.
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