Estrogens Induced Male Production at a Female-Producing Temperature in a Reptile (Leopard Gecko, Eublepharis Macularius) with Temperature-dependent Sex Determination

Abstract

Estrogens and estrogen mimics can affect offspring sex ratios in a wide variety of animal species including Leopard Geckos, Eublepharis macularius, a species with temperature-dependent sex determination (TSD). Estrogens can disrupt effects of temperature on sex determination by feminizing or sex-reversing embryos incubated at male-producing temperatures. Estrogens may have paradoxical effects at different incubation temperatures and in different concentrations. In this study, E. macularius eggs were exposed to ethanol, estradiol benzoate, or estradiol 17b at the beginning of the thermosensitive period when sex determination occurs. Eggs were treated and incubated at each of three incubation temperatures known to produce varying primary sex ratios. At a male-producing incubation temperature, estrogen-treated groups produced more females than negative control groups. This result has been reported in other TSD reptiles. In our study, we showed that at a female-producing incubation temperature, estrogen-treated groups produced significantly more males than negative control groups. This is the first report of its kind in which a TSD reptile was shown to produce significantly more males at a female-producing temperature. Our results suggest a complex feedback relationship between aromatase and cofactors during the thermosensitive period of egg incubation in E. macularius. Expected effects of exogenous estrogens on contaminant-exposed wildlife populations may differ depending on nest-site temperatures. In species with temperature-dependent sex determination (TSD), sex is determined by the temperature to which an embryo is exposed during a thermally sensitive period of incuba- tion. The influence of exogenous estrogens on