Meeting Abstract
Vertebrate embryos develop within an environment containing maternal steroid hormones that are transferred during oogenesis or gestation, which may have either transient of persistent effects during embryonic development. In egg-laying vertebrates, the amount of steroids a female transfers via yolk to the eggs she lays can vary, and this variation has been hypothesized to adaptively modify offspring phenotype. Yet, embryos are known to actively regulate their maternal steroid exposure, which raises the question: How important are maternal steroids to embryonic development? In the in ovo study, we used European starling (Sturnus vulgaris) eggs to examine the fate of yolk testosterone early in development. Tritiated testosterone (3H-T) was injected into freshly laid eggs which were then sampled over the first five days of incubation to characterize the movement and metabolism of 3H-T. After only 12 hours of incubation, the overwhelming majority of the 3H-T had been metabolized. Various metabolites, primarily etiocholanalone, were detected within the yolk. We then used yolk and albumen from unincubated eggs to assess 3H-T metabolism in vitro and found that the patterns of metabolism within the yolk were largely similar to those reported in the in ovo study. Given the rapid pace at which 3H-T is metabolized, both in ovo and in vitro, the extent to which maternal testosterone ever influences the embryo prior to being metabolized is unclear. The phenotypic effects of maternal testosterone may thus be mediated by the small amount of non-metabolized testosterone, the large amount of etiocholanolone produced, or both.
