Meeting Abstract

P3.23  Monday, Jan. 6 15:30  Within-clutch Patterns of Yolk Steroids: Does Egg Collection Method Matter? CASTO, J.M.*; SMITH, A.R.; DE BIASIO, D.; Illinois State University; Illinois State University; Illinois State University jmcasto@ilstu.edu

Oviparous vertebrates transfer steroid hormones to egg yolk during folliculogenesis, and these hormones can influence offspring development. In birds, variation in within-clutch patterns of maternal steroid transfer has prompted adaptive explanations, such as parental favoritism of early- or late-laid eggs. However, these patterns may also be influenced by steroid metabolism occurring before the eggs are collected. Very early in embryogenesis, yolk steroids such as testosterone (T), corticosterone (B) and progesterone are metabolized and conjugated to water-soluble forms, but these processes require developing embryos. If embryonic steroid metabolism begins in eggs prior to clutch completion, then whether the eggs are collected and frozen individually on the day they are laid or collected as a group after completion of laying could influence the concentration of steroid hormones detectable in individual eggs. In turn, this could affect measured within-clutch patterns of steroid concentration such that patterns of variation among eggs could be created, eliminated, intensified or minimized by the specific collection method. Here we test the effects of two published egg collection regimens – collected either individually on the day of laying or as an entire clutch after laying ceases – on within-clutch patterns of yolk steroid concentrations in the eggs of European starlings (Sturnus vulgaris). Preliminary data from a subset of clutches suggest that for eggs laid earlier in clutches (but not later laid eggs), both yolk T and B titers tend to be higher in clutches in which eggs were collected daily than in clutches collected once laying ceased. If confirmed, this pattern likely reflects the onset of steroid metabolism in laid eggs prior to clutch completion.