TEMPERATURE-DEPENDENT SEX DETERMINATION IN THE SNAPPING TURTLE - MANIPULATION OF THE EMBRYONIC SEX STEROID ENVIRONMENT

In certain reptiles with temperature-dependent sex determination (TSD) , estrogens act as a signal for female differentiation. Because aromat ase produces estrogens from androgens, this enzyme plays a pivotal rol e in TSD. Whether androgens act as the signal for male differentiation in TSD species is not yet clear. We manipulated the hormonal environm ent in eggs of the common snapping turtle (Chelydra serpentina) to det ermine the effects of an estrogen (estradiol 17-beta), an aromatase in hibitor (fadrozole; CGS 16949A), and androgens (testosterone and dihyd rotestosterone) on sex determination in this TSD species. Test solutio ns were applied topically to representative eggs (total tested = 1054 from 27 clutches) and incubated at two male-producing temperatures (24 and 26.5 degrees) and at a predominantly female-producing temperature (29 degrees). In this species, application of an estrogen induced fem ale development at all temperatures tested. In contrast, the aromatase inhibitor had no effect at the male-producing temperatures, but induc ed male development at the predominantly female-producing temperature. At this temperature, aromatase inhibitor plus testosterone had a simi lar male-producing effect, but when applied alone, testosterone failed to augment male production. Dihydrotestosterone had a similar effect, in contrast to its reported androgenic effects in other TSD species. In the snapping turtle, male differentiation may not be androgen depen dent; rather, it may proceed in the absence of female differentiation. In this species, female development is clearly estrogen-dependent and is altered by aromatase inhibition at female-producing temperatures. Our results not only provide additional evidence that sex steroids med iate gonadal differentiation in TSD species, but also suggest caution with respect to generalizations about the proximal mechanisms of TSD i n reptiles. (C) 1994 Academic Press, Inc.