Ontogenetic Aspect of Steroidogenesis by Gonads and Adrenals of Ducks and Its Role on Sex Differentiation

Abstract

Plasma testosterone, estradiol, corticosterone and cortisol levels together with gonadal testosterone and estradiol concentrations were determined by radioimmunoassay in the embryonic and post-embryonic Domestic Duck, Anas platyrhynchos var. domestica. The plasma testosterone and estradiol concentrations were higher in the female than in the male embryo, whereas no sex-difference was observed either in plasma corticosterone or cortisol. Both the ovarian estradiol and testosterone concentrations in the embryo were much higher in the testicular concentrations. The plasma corticosterone or cortisol concentration reached a peak one day after hatching, and decreased thereafter in both sexes. These results indicate that the ovary of embryonic duck is more active in secreting the sex steroid hormones than the embryonic testes, and suggest that the original sex of the duck (probably of all avian species) should be male (ZZ), and estrogenic hormones secreted from the embryonic ovary has an important role in sexual development (feminizing) of the female in the duck.