Specificity of steroid hormone-induced sex determination in a turtle.

The specificity of steroid hormone-induced sex determination was investigated in the red-eared slider, Trachemys scripta, a turtle with temperature-dependent sex determination. All eggs were incubated at either a female-producing temperature (31 degrees C) or a male-producing temperature (26 degrees C) and received control or experimental treatments at stage 17-18 of embryonic development. A variety of treatments induced female sex determination at the male-producing temperature. Oestradiol-17 beta, diethylstilboestrol (DES) (an oestrogen agonist) and norethindrone (NET) (a progestin with reputed oestrogenic as well as anti-oestrogenic properties) were the most effective in inducing female sex determination. Other reputed oestrogen antagonists/partial agonists (i.e. tamoxifen, nafoxidine and clomiphene citrate) were also capable of inducing female sex determination, but to a lesser extent. A high dosage of testosterone resulted in the production of some females (7 of 15 hatchlings) whereas dihydrotestosterone had no detectable effect on sex determination. This latter finding suggests that testosterone could be acting via aromatization to oestradiol-17 beta. A few females resulted from eggs that had been treated with aromatase inhibitor, 1,4,6-androstatrien-3,17-dione (ATD) (3 of 97), the antiandrogen hydroxyflutamide (1 of 55) and progesterone (3 of 36), suggesting the possibilities of non-specific effects of these compounds when used in large dosages. Alternatively, metabolites of these compounds may be oestrogenic. Collectively, the results at the male-producing temperature are consistent with the hypothesis that steroid-induced female sex determination is mediated via an oestrogen-specific receptor.(ABSTRACT TRUNCATED AT 250 WORDS)