Meeting Abstract

S5-2.3  Friday, Jan. 4  Hormone-mediated Maternal Effects in Birds: Mechanisms GROOTHUIS, T G G *; SCHWABL, H; University of Groningen, NL; Washington State University Pullman, USA

Over the past decade birds have proven to be excellent models to study steroid hormone-mediated maternal effects in an evolutionary framework. Most studies focus on the function of maternal steroid hormones for offspring development but lack of knowledge about the relevant underlying mechanisms hampers further progress. We discuss hypotheses concerning these mechanisms, point out their relevance for ecological and evolutionary interpretations and review the relevant data. We first examine whether maternal hormones can accumulate in the egg independently of changes in hormone concentrations in the maternal circulation. This is relevant for Darwinian selection and female physiological trade-off. Next we discuss embryonic utilization of maternal steroids, since enzyme and receptor systems in the embryo may have co-evolved with maternal effect mechanisms in the mother. We also consider the importance of dose-response relationships and effect pathways of androgens and argue that this may help in understanding the lack of interference of maternal steroids with the process of sexual differentiation. Finally, we discuss mechanisms underlying the many pleiotropic actions of maternal steroids, since linked effects may limit evolution by causing physiological trade-offs. We urge endocrinologists to embark on mechanistic studies and behavioural ecologists to adjust their interpretation to the current knowledge of mechanisms.