Reproductive cycle of female Chinese green tree vipers, Trimeresurus stejnegeri stejnegeri, in northern Taiwan

From March 1996-August 1997, we studied the reproductive cycle of 132 female Chinese green tree vipers, Trimeresurus stejnegeri stejnegeri, in northern Taiwan by examining seasonal changes in their hormone levels and reproductive organ morphology and histology. Based on follicle size and the presence or absence of corpora lutea, we classified each female into one of five reproductive cycle stages. Ovulation occurred in stage IV while stage V was the post-partum stage. Liver mass peaked during stages II and III when vitellogenin is demanded for vitellogenesis. Changes in kidney mass and fat body mass paralleled changes in liver mass. Most histological characters of the oviduct, including epithelium height and gland diameter, increased gradually during stages I through III, and declined thereafter. Serum progesterone concentration peaked in stage IV while serum estradiol peaked in stage III. Stage I females were considered non-reproductive while females in stages II to V were classified as reproductive. The ratio of reproductive to non-reproductive females was nearly 1:1. However, the proportion of reproductive females increased significantly with female body size. These results suggest that female Chinese green tree vipers have the potential to breed annually but often reproduce less than once per year. Like crotaline snakes from temperate areas, female Chinese green tree vipers in northern Taiwan exhibited low-frequency reproduction, postnuptial vitellogenesis, and long-term sperm storage.