Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada, B3H 4R2.
Biol Lett. 2012 Dec 23;8(6):1055-8. doi: 10.1098/rsbl.2012.0476. Epub 2012 Jul 18.
Hormonally mediated maternal effects link maternal phenotype and environmental conditions to offspring phenotype. The production of lipid-rich maternal yolk precursors may provide a mechanism by which lipophilic steroid hormones can be transported to developing yolks, thus predicting a positive correlation between yolk precursors in mothers and androgen levels in eggs. Using rockhopper penguins (Eudyptes chrysocome), which produce a two-egg clutch characterized by extreme egg-size dimorphism, reversed hatching asynchrony and brood-reduction, we examined correlations between circulating concentrations of the primary yolk-precursor vitellogenin (VTG) and levels of yolk androgens. Previous work in Eudyptes penguins has shown that egg-size dimorphism is the product of migratory constraints on yolk precursor production. We predicted that if yolk precursors are constrained, androgen transport to developing yolks would be similarly constrained. We reveal positive linear relationships between maternal VTG and androgens in small A-eggs but not larger B-eggs, which is consistent with a migratory constraint operating on the A-egg. Results suggest that intra-clutch variation in total yolk androgen levels depends on the production and uptake of yolk precursors. The brood reduction strategy common to Eudyptes might thus be best described as the result of a migratory constraint.
激素介导的母体效应将母体表型和环境条件与后代表型联系起来。富含脂质的母体卵黄前体的产生可能提供了一种机制，通过该机制亲脂性甾体激素可以被运输到正在发育的卵黄中，从而预测母体卵黄前体与卵中雄激素水平之间存在正相关关系。使用跳岩企鹅（Eudyptes chrysocome），其产生两个卵的卵，其特征是卵大小的二态性极端，孵化反序和繁殖减少，我们检查了循环中的主要卵黄前体卵黄蛋白原（VTG）浓度与卵黄和雄激素水平之间的相关性。在 Eudyptes 企鹅中的先前研究表明，卵大小的二态性是卵黄前体产生受迁徙限制的产物。我们预测，如果卵黄前体受到限制，那么向发育中的卵黄运输雄激素也会受到类似的限制。我们揭示了小 A 卵中的母体 VTG 和雄激素之间存在正线性关系，但在较大的 B 卵中则没有，这与在 A 卵上起作用的迁徙限制一致。结果表明，总卵黄雄激素水平的巢内变异取决于卵黄前体的产生和摄取。因此，Eudyptes 中常见的繁殖减少策略最好被描述为迁徙限制的结果。
