Female birds can’t reproduce without male sex hormones, study finds Premium

New research shows androgen receptors are crucial for sexual development and fertility in both male and female chickens.

The androgen sex hormones are responsible for male sexual development while oestrogen and progesterone essay the same roles in females. But new research by a team at the Max Planck Institute of Biological Intelligence and Technical University, Munich, could force scientists to redraw these boundaries. The team has reported that androgen receptors are as important for sexual development and fertility in females as in males.

Specifically, the researchers found that both male and female chickens devoid of androgen receptors turned out to be infertile. But the males still developed testicles and the females ovaries, and produced gonadal hormones. The testicles and ovaries were smaller than in chickens that retained their androgen receptors.

Additionally, female chickens that lacked the receptors failed to develop and lay eggs. And while a few sex-specific peculiarities like tail feathers, spurs, and differences in body size and weight persisted in both sexes, their sexual behaviours failed to develop. Their eye rings remained unpigmented as well.

“For years, one of the key players in avian sexual development has been reported to be testosterone, a steroid hormone belonging to the class of hormones called androgens, commonly thought of as only a male hormone,” Mekhla Rudra, a scientist at the Max Planck Institute of Biological Intelligence and a coauthor of the study, said. “One of the key insights this study provides is that testosterone action via androgen signalling is critical in both male and female birds.”

“The study illustrates that androgen receptors directly influenced diverse tissues leading to sex-specific phenotypes. In females, too, the effects of androgens are to promote the development of head ornaments and normal ovarian follicle,” Peter O’Shaughnessy, a scientist at the University of Glasgow who wasn’t involved in the study, said.

Androgen hormones are known to decrease body weight in chickens. Male chickens in commercial settings are thus castrated to prevent androgen secretion and thus increase their bodyweight.

In birds, androgen and oestrogen receptors help regulate sexual development by mediating the actions of these hormones. Unlike mammals, avian somatic cells (cells other than sperm and ova) also manifest sexual traits independent of hormonal influences. “These characteristics are independent of hormonal influence,” Rudra said.