High temperatures influence sexual development differentially in male and female tadpoles of the Indian skipper frog, Euphlyctis cyanophlyctis.

Abstract

Although sex determination in amphibians is believed to be a genetic process, environmental factors such as temperature are known to influence the sex differentiation and development. Extremely low and high temperatures influence gonadal development and sex ratio in amphibians but the mechanism of action is not known. In the present study, effect of different temperatures on gonadal development, sex ratio and metamorphosis was studied in the Indian skipper frog, Euphlyctis cyanophlyctis. The embryos of Gosner stage 7 were exposed to 20, 22, 24, 26, 28, 30 and 32 degrees C up to tadpole stage 42. The embryos (stage 7) were also exposed to 20 and 32 degrees C up to tadpole stage 25 (non-feeding stages). Tadpoles of stage 25 were reared at 20 and 32 degrees C up to stage 42 (feeding stages). The results show that exposure to higher temperatures (28, 30 and 32 degrees C) during stages 7-42 produced male-biased sex ratio. Rearing of tadpoles at 32 degrees C during stages 25-42 produced malebiased sex ratio, while exposure during stages 7-25 did not affect sex ratio. Embryos and tadpoles exposed to lower temperatures (20 and 22 degrees C) died during the early stages. High temperatures stimulated testis development, and disturbed ovary development. Exposure to high temperatures resulted in the early metamorphosis of tadpoles with reduced body size. These results demonstrated that high temperatures influence gonadal development differently in male and female tadpoles, leading to male-biased sex ratio. These results suggest that high temperature probably acts through stress hormones and favours the small-sized sex.