AMES, C.A.; WILLIAMS, T.D. *; Simon Fraser Univ., Burnaby: Laying sequence-specific manipulation of maternal hormone profiles: effects on offspring phenotype

Although it is becoming clear that maternal transfer of steroids to yolk can have significant effects on offspring phenotype, a major unresolved issue is whether variation in yolk steroids reflect an adaptive, facultative �decision� by the mother or an indirect, �non-adaptive� consequence of variation in the maternal hormonal milieu? One way to investigate this is to manipulate the endogenous, laying sequence-specific pattern of maternal hormone secretion (assuming this is know) and determine sequence-specific effects on offspring phenotype. Previous studies have shown that in laying birds plasma levels of 17 beta-estradiol increase rapidly to maximum levels at the 1-egg stage and then decrease during laying reaching low levels before final oviposition. We manipulated plasma E2 to maintain chronic high levels throughout laying, altering the hormonal milieu for developing yolks, and investigated effects on laying and offspring development. Preliminary validation of our E2 stock solution revealed repeatable, individual variation in the sensitivity to E2 injections in non-breeders as measured by plasma vitellogenin response. In laying birds, VTG at the 5-egg stage was higher in E2 birds compared with controls (4.0 vs 0.07 ug/ml zinc), but there was no difference in timing of ovarian development or oviduct regression. We will also report effects on hatchability, chick growth and fledging success and sequence-specific sex ratio in relation to E2 treatment.