Impact of endocrine disrupting chemicals on reproduction in Japanese quail

Abstract

Many environmental contaminants can interact with the endocrine system, thereby potentially disrupting the reproductive fitness of individuals. In avian species, the egg-yolk is a major route for excretion of lipophilic compounds by the adult female bird and embryos are exposed to contaminants that have been deposited in the eggs. The reproductive and neuroendocrine system of Japanese quail undergoes sexual differentiation during embryo development. The phenotypic sex, including sex-specific adult behavior, is hormonally imprinted already before hatching. The sexual differentiation of the brain in quail is sensitive to estrogens and the presence of estrogen results in a female phenotype. The relatively low concentration of estrogens in male embryos, on the other hand, results in a male behavioral phenotype. The behavior of male quail can be demasculinized by estrogen exposure during the period of sexual differentiation, and estrogen-exposed males are not able to display a male-typical behavior as adults. Also, differentiation of the reproductive organs is sensitive to hormones during embryogenesis, and an excess of estrogens can for instance induce persistent morphological changes in the reproductive organs of females. Our research has focused on effects in adult birds after embryonic estrogen exposure. We have studied sexual behavior and other reproductive variables in adult quail after in ovo injection of known and suspected estrogenic compounds. Synthetic estrogens and insecticides, such as o, p′-DDT altered the development of the neural system and resulted in demasculinization of male quail. In females, o, p′-DDT caused morphological changes of the oviduct and egg laying was reduced. Our studies suggest that the neural system and the female reproductive system of avian embryos are very sensitive to the effects of chemicals with estrogenic activity.