Throat patch size and darkness covaries with testosterone in females of a sex-role reversed species

In male birds, size and blackness of melanin-based ornaments may signal competitive ability and quality. Testosterone is an important physiological mediator of these signals as these ornaments are testosterone dependent. Experimental manipulation of circulating testosterone in females suggests that similar mechanisms are at work in plumage ornaments of females. However, hormone manipulations typically result in testosterone levels that are far higher than physiological concentrations experienced by females. Thus, it remains unclear whether natural variation of testosterone levels would be sufficient to generate variation in female plumage coloration. A signaling value of plumage ornamentation is particularly important in females of sex-role reversed species, in which females are the more competitive sex. We examined the relationship between plumage coloration, body condition, and circulating testosterone in female barred buttonquails (Turnix suscitator), a classically polyandrous species. Even though female testosterone levels were low, they were strongly positively related with body condition and the size and blackness of the melanin throat patch. In males, no such relationships were apparent, suggesting that females may have an enhanced sensitivity for testosterone or its metabolites. These unique results reveal that a hormonal mechanism may be involved in sex-role reversal in this species. Copyright 2011, Oxford University Press.