MECHANISMS AFFECTING REPRODUCTION AND ORNAMENT EXPRESSION IN MALE TETRAONIDAE BIRDS

Abstract

Most avian species have breeding seasons that are appropriate for their survival. The hypothalamic-pituitary-testicular axis controls the endocrine system and the onset of breeding. The Tetraonidae (a family of birds in the order Galliformes) live in extreme environments where their breeding season is restricted by ambient factors, particularly day length. In the breeding season, male Tetraonidae birds prominently express combs over their eyes (supraorbital combs), the expression of which is controlled by testosterone, a well-known androgen. Testosterone also regulates immunocompetence and there is a trade-off between the cost for condition and the benefit for reproduction in the expression of sexual traits like the comb. Thus, the comb may be the specific indicator projecting male quality. This article reviews the effects of the endocrine system on reproduction and expression of the comb in male Tetraonidae.