Exogenous application of estradiol to eggs unexpectedly induces male development in two turtle species with temperaturedependent sex determination

Abstract

<p><a href="http://topics.sciencedirect.com/topics/page/Steroid_hormones">Steroid hormones</a> affect sex determination in a variety of vertebrates. The feminizing effects of exposure to <a href="http://topics.sciencedirect.com/topics/page/Estradiol">estradiol</a> and the masculinizing effects of <a href="http://topics.sciencedirect.com/topics/page/Aromatase">aromatase</a> inhibition during development are well established in a broad range of vertebrate taxa, but paradoxical findings are occasionally reported. Four independent experiments were conducted on two turtle species with temperature-dependent sex determination (<em>Chrysemys picta</em> and <em>Chelydra serpentina</em>) to quantify the effects of egg incubation temperature, estradiol, and an <a href="http://topics.sciencedirect.com/topics/page/Aromatase_inhibitor">aromatase inhibitor</a> on offspring sex ratios. As expected, the warmer incubation temperatures induced female development and the cooler temperatures produced primarily males. However, application of an aromatase inhibitor had no effect on offspring sex ratios, and exogenous applications of estradiol to eggs produced male offspring across all incubation temperatures. These unexpected results were remarkably consistent across all four experiments and both study species. Elevated concentrations of estradiol could interact with <a href="http://topics.sciencedirect.com/topics/page/Androgen_receptor">androgen receptors</a> or inhibit aromatase expression, which might result in relatively high <a href="http://topics.sciencedirect.com/topics/page/Testosterone">testosterone</a> concentrations that lead to testis development. These findings add to a short list of studies that report paradoxical effects of steroid hormones, which addresses the need for a more comprehensive understanding of the role of <a href="http://topics.sciencedirect.com/topics/page/Sex_steroid">sex steroids</a> in sexual development.</p>