NAVARA, KJ*; SIEFFERMAN, LM; HILL, GE; MENDON�A, MT; Auburn University, AL; Auburn University, AL; Auburn University, AL; Auburn University, AL: Yolk androgens differ independently of maternal androgens in eastern bluebirds: an experimental study

Avian females deposit variable amounts of androgen into the yolks of their eggs, a potentially adaptive mechanism for altering offspring quality. It is unclear, however, whether yolk androgen deposition represents a passive reflection of circulating plasma androgens in the female during follicular development or an active shuttling of androgens in response to a social or environmental cues. We stimulated breeding pairs of eastern bluebirds with an intruder presentation during ovarian follicular development. We then compared yolk steroid concentrations in the eggs of stimulated females with yolk steroid concentrations in the eggs of control females. Additionally, we took blood samples from subsets of stimulated and control females and compared hormone profiles of eggs with hormone profiles of female plasma, both independently of and in relation to our experimental design. Regardless of experimental treatment group, patterns of steroid concentrations differed between egg yolks and female plasma. In relation to our experiment, stimulated females deposited significantly more androgens into eggs than control females, suggesting that females increase yolk androgen deposition in response to aggressive encounters. Female plasma androgens, however, were significantly lower in stimulated females than in controls, the complete opposite of concurrently observed yolk patterns. We suggest that eastern bluebirds regulate hormone levels in an adaptive manner in response to environmental change by actively shuttling androgen into eggs. Eggs may act as a sink for the collection of androgens that are produced in response to aggressive encounters. Thus, yolk androgen deposition may be a protective mechanism against androgen-related disruptions of the female reproductive cycle.