BENOWITZ-FREDERICKS, Z.M.; KITAYSKY, A.S.; SHULTZ, M.T.; WINGFIELD, J.C.; Univ. of Washington, Seattle; Univ. of Washington, Seattle; USGS, Alaska Biological Sciences Center; Univ. of Washington, Seattle: Steroid hormones in yolk and allantoic waste of Common murres (Uria aalge) – patterns within a subcolony

In this study we examined temporal patterns of steroid levels in egg yolk in a subcolony of Common murres (Uria aalge), colonial seabirds that lay a single egg. Most studies of steroid hormones in avian egg yolk address within-clutch variation in hormone levels in terms of its role in mitigating effects of hatching asynchrony. A common finding is that later-laid eggs contain more androgens (testosterone and a precursor: androstenedione) – embryonic exposure to androgens has been shown to increase chick growth and aggressiveness. Common murre subcolonies are analogous to multi-chick broods – late-hatched chicks are under pressure to fledge at a younger age in order be synchronous with their earlier-hatched neighbors. Thus, we predicted higher androgen levels in later-laid eggs within a subcolony. We assessed embryonic exposure to steroids in two ways. First, we compared hormone levels in the yolk of earlier- and later-laid eggs from a subcolony. Later-laid eggs contained significantly higher amounts of androstenedione, but there were no significant differences in testosterone levels. Second, we examined steroid hormone levels in allantoic waste of earlier- and later-hatched chicks from a subcolony. Steroid levels in allantoic waste reflect everything processed by the embryo – of both maternal (yolk) and endogenous origin. We found a significant negative relationship between levels of several steroid hormones and hatch date and growth parameters, but no significant relationships with testosterone. These results suggest that murre females do not alter testosterone deposition in yolk with respect to timing of laying, but do alter its precursor, androstenedione.