Action of sex steroid hormones on temperature-induced sex determination in the snapping turtle (Chelydra serpentina)

Developmental abnormalities of the gonad and abnormal sex hormone concentrations in juvenile alligators from contaminated and control lakes in Florida.

“…Specifically, estrogen treatment of alligator (41) and turtle (42)(43)(44) eggs incubated at male-producing temperatures can cause sex reversal and the production of apparently normal females. Crews et al (44) found that estradiol benzoate (EB) or an estrogen agonist (R2858) were equally effective in inducing turtle embryos to develop as females when eggs were incubated at maleproducing temperatures. Further, they * -3 --I hi found that -some of the EB-treated turtle embryos exhibited hypertrophied oviducts (44).…”

“…Crews et al (44) found that estradiol benzoate (EB) or an estrogen agonist (R2858) were equally effective in inducing turtle embryos to develop as females when eggs were incubated at maleproducing temperatures. Further, they * -3 --I hi found that -some of the EB-treated turtle embryos exhibited hypertrophied oviducts (44). As in turtles, alligator eggs incubated at a male-producing temperature and treated with 100 pg or 300 pg EB/egg induced sex reversal in 100% of the eggs so treated (41) E2 and T indicate that no turtle hatchling from Lake Apopka produces a normal androgen synthesis pattern (Gross and Guillette, unpublished data).…”

The ends of a continuum: genetic and temperature‐dependent sex determination in reptiles

“…(53) This process acts to shift the endocrine balance between male and female differentiation in the developing embryo. (39)(40)(41) Extraordinary conservatism across vertebrate orders in the genes involved in sexual differentiation, and the clear potential for some of these conserved genes to be involved in sexual determination, suggests that differences at the molecular level among reptiles with different sex-determining mechanisms might be small, potentially involving a few or perhaps only one gene.…”

“…(37) There is general consensus that temperature exerts its influence in species with TSD by acting upon the genetic mechanisms that govern steroidogenic enzymes or steroid hormone receptors, thus altering the hormone environment of the sexually indifferent embryo and directing development in either a male or a female direction. (22,38) Administration of exogenous oestrogen in turtles will override the effect of a male-producing temperature to yield female hatchlings (39,40) and the period of sensitivity to exogenous oestrogen coincides with the thermosensitive period. (41) In reptiles, synthesis of oestrogens depends on the aromatization of testosterone and androstenedione to the oestrogens estrone and estradiol-17b.…”

“…In TSD reptiles, the inhibitors have a progressively more potent effect as the pivotal range is approached. Mechanisms by which sexual differentiation is influenced by the hormonal environment, involving androgens, oestrogens and aromatase, are conserved across birds (GSD), (42) reptiles (TSD), (40) amphibians (43) and fish. (8) In TSD reptile species, temperature exerts an influence at some point in the otherwise highly conserved and complex sequence of steps that leads to differentiation of the gonad.…”