Steroids in allantoic waste: an integrated measure of steroid exposure in ovo.

Recent studies examining patterns and consequences of variation in maternally deposited steroids in avian egg yolk have demonstrated that these maternal hormones can have dramatic effects on chick phenotypes. However, maternal steroids are not the only source for avian embryos, which activate endocrine axes relatively early in development and are capable of producing substantial amounts of endogenous steroids. Although organizational effects of steroids have been demonstrated, the interactions between steroids from yolk and endogenous production have not been addressed. Steroids in the yolk are likely to alter development of the embryo's endocrine axes. The ability to assess total steroid exposure in ovo in a nonlethal fashion would improve our understanding of these interactions and help elucidate the mechanisms by which maternal steroids alter chick phenotype. Steroid levels in allantoic waste provide a cumulative measure of steroids excreted in ovo and may prove to be a useful tool. We present data from semiprecocial seabirds, common murres, demonstrating the presence of detectable steroids in allantoic waste and suggesting that some reflect differences in timing of hatching and may provide information about aspects of chick phenotype.