Sex reversal by testosterone and not by estradiol or temperature in Calotes versicolor, the lizard lacking sex chromosomes

Abstract

The garden lizard Calotes versicolor lacks identifiable sex chromosomes. The present study demonstrates that temperature has no apparent effect on the determination of sex. In embryos reared at higher temperature (32°, 34°, 35°C), the gonads differentiate earlier than in controls and the overall duration of embryonic incubation is dramatically reduced. Exogenous administration of testosterone (100 µg/egg) to embryos of stages 28, 30, and 33 results in the majority of them developing into males; no female is encountered. Testosterone also accelerates the differentiation of testes. Estradiol (5, 10, µg/egg), administered at the same stages as testosterone, does not show any effects on gonadal differentiation. These results indicate that in C. versicolor, female is the default sex and the male is heterogametic. Apparently, this is the first report in a reptile in which testosterone has been shown to cause reversal into male sex.