Studies on sex determination in the American alligator Alligator mississippiensis

Estradiol-17β was measured in the plasma and urogenital tissues of male and female alligator embryos. Hormone levels were generally very low and there was no significant differences between the sexes. There were no significant changes in estrogen levels during the period of gonadal differentiation in either sex. Alligator embryos incubated at male producing temperatures were feminized by small doses of estrogen applied to the egg shell. The antiestrogen, tamoxifen, masculinizes turtle and bird embryos, but, paradoxically, feminized alligator embryos at male producing temperatures. The contraceptive steroid, norethindrone, a progestin that is claimed to block estrogen synthesis, is the most potent estrogenic steroid tested on alligator embryos. A single dose of norethindrone applied to the egg shell caused massive hypertrophy of the Mullerian duct and feminized embryos at male producing temperatures. The androgen, dihydrotestosterone, had no detectable effect on male or female embryos at the doses tested. Undifferentiated urogenital tracts of embryos were cultured at 30 and 33°C in the presence of steroids, tamoxifen, or antibodies to steroids. None of the treatments had any effect on tissue differentiation. Tissues survived for up to 6 weeks, but there was no evidence of gonadal differential in vitro. © 1994 Wiley-Liss, Inc.