WILLIAMS, T.D. *; VEZINA, F.; KITAYSKY, A.S.; Simon Fraser University, Burnaby; Simon Fraser University, Burnaby; University of Washington, Seattle: Estradiol: a neglected hormone in maternal modification of offspring phenotype?

Many current studies suggest that transfer of maternal steroid hormones to the developing embryo might play a role in non-genetic modification of offspring phenotype. However, to date these studies have focussed almost exclusively on the effects of androgens (e.g. testosterone, androstendione, 5-DHT), in part because of low or non-detectable levels of yolk estrogens in many studies. Although laying female birds can have elevated levels of plasma androgens it seems likely that the hormonal state of females during laying will be dominated by estrogens, in particular 17beta-estradiol (E2). Here we describe inter-individual and stage-dependent variation in plasma E2 levels during the laying cycle in European starlings (Sturnus vulgaris). At the 1-egg stage there was marked inter-individual variation in plasma E2 levels in birds with a full ovarian follicle hierarchy (5-6 yolky follicles): 69 – 423 pg/ml. This variation was not related to egg mass, total follicle mass, or mass of the F1 follicle. E2 levels peaked at the 1-egg stage (236 � 16 pg/ml) but then decreased rapidly and linearly with laying of subsequent eggs, such that at the 4-egg stage levels were not significantly different from those in non-breeders (54 pg/ml). Thus, early and late developing follicles undergo rapid yolk development under very different female hormonal ‘states’: high and low E2 respectively. Data on variation in plasma testosterone will also be presented. We have previously shown that E2-treatment of mothers can affect offspring sex ratio and daughters egg size (Horm. Behav. 35:135). These results suggest that future work should focus on E2, not just androgens, in relation to maternal modification of offspring phenotype.