Endoscopic Imaging of Gonads,Sex Ratio and Temperature Dependent Sex Determination in Captive Bred Juvenile Burmese Star Tortoises Geochelone platynota

摘要

The possibility of temperature dependent sex determination makes it important to evaluate sex ratios in captive breeding programs of threatened tortoises.We assessed the sex ratio of juvenile Burmese Star Tortoises Geochelone platynota by direct observation of their gonads through an endoscope in the captive breeding program of the Behler Chelonian Center(BCC)in California.The gonads of small juvenile G.platynota are thin and elongate,and f ixed to the dorsal part of body cavity,with ovaries appearing as transparent sheaths with some oocytes visible and testes appearing as small,transparent,thin,sausage-like structures with a net of fi ne blood vessels on the surface.With growth,ovaries expand and masses of pre-vitellogenic follicles appear on the surface.Testes are transparent in small juveniles and,with growth,turn pinkish-white and then yellowish,with tubuli structures visible through a thin,transparent theca containing a network of fi ne blood vessels.Egg incubation temperatures were not rigorously monitored,but a temperature of 28.9°C produced a heavily male biased sex ratio whereas a temperature of 30°C produced a balanced sex ratio.This suggests that G.platynota has temperature dependent sex determination.