JOHNSTON, G.I.H.**; MOORE, M.C.; Arizona State University; Arizona State University: Transfer of Maternal Corticosterone to Yolk in Preovulatory and Postovulatory Tree Lizard (Urosaurus ornatus) Eggs

Eggs of many vertebrates contain yolk steroids of maternal origin, which can profoundly influence offspring development, growth, and behavior. How and when steroids get into the yolk is still not clear. Are they intentionally deposited or just incidentally taken up? We are particularly interested in the effects that maternal stress hormones, such as corticosterone, can have on offspring. In this study we examined when the eggs are susceptible to elevated maternal corticosterone levels. We implanted both vitellogenic (preovulatory) and gravid (postovulatory) tree lizards (Urosaurus ornatus) with corticosterone. It is usually assumed that maternal steroids are deposited into yolk during egg formation, so we predicted that implanting the mother during vitellogenesis would elevate yolk hormone levels. However, since there is no longer a large blood supply to the shelling eggs in the oviduct, we predicted that high maternal corticosterone levels during gravidity would have little effect on yolk corticosterone levels. Surprisingly, yolk corticosterone was elevated in eggs from females implanted both while vitellogenic and while gravid. We believe this is the first evidence that maternal steroids can be deposited into oviductal eggs. This finding greatly increases the time window during egg production when eggs are susceptible to influence by maternal steroids, especially in species like tree lizards in which the eggs can remain in the oviduct for 10-30 days and perhaps longer.