Centre for Ecology and Hydrology, Natural Environment Research Council, Penicuik, Midlothian, Scotland, United Kingdom.
Am Nat. 2010 Sep;176(3):357-66. doi: 10.1086/655223.
Where life-history stages overlap, there is the potential for physiological conflicts that might be important in mediating carryover effects. However, our knowledge of the specific physiological mechanisms underlying carryover effects remains rudimentary, and specific examples remain rare. Here we show that female macaroni penguins (Eudyptes chrysolophus) initiate vitellogenesis and yolk formation while at sea during return migrations to breeding colonies; yolk formation takes approximately 16 days, but females lay only 7-14 days after their return. Once on land, Eudyptes penguins show a unique reproductive pattern of extreme egg size dimorphism in which the smaller, first-laid A-egg is 55%-75% of the size of the larger B-egg. We show that the degree of egg size dimorphism is inversely correlated with time between arrival and laying; that is, females that begin reproductive development well in advance of their return produce more dimorphic eggs. Furthermore, late-arriving females that produce the most dimorphic eggs have lower plasma levels of the yolk precursor vitellogenin on arrival; that is, they show lower reproductive "readiness." These data support the hypothesis that extreme egg size dimorphism in Eudyptes penguins is due to a physiological constraint imposed by a migratory carryover effect and argue against small A-eggs having a specific, adaptive function.
在生活史阶段重叠的地方，可能存在生理冲突的潜力，这些冲突可能在介导代谢效应中很重要。然而，我们对代谢效应背后的具体生理机制的了解仍然很初级，具体的例子仍然很少。在这里，我们表明，在返回繁殖地的迁徙过程中，雌性麦哲伦企鹅（Eudyptes chrysolophus）在海上就开始进行卵黄生成和卵黄形成；卵黄形成大约需要 16 天，但雌性在返回后的 7-14 天内产卵。一旦在陆地上，Eudyptes 企鹅表现出一种独特的生殖模式，即极端的卵大小二态性，其中较小的、先产的 A 卵是较大的 B 卵的 55%-75%。我们表明，卵大小二态性的程度与到达和产卵之间的时间呈负相关；也就是说，那些在返回前很早就开始生殖发育的雌性会产生更多二态性的卵。此外，到达时间较晚但产生最二态性卵的雌性在到达时的卵黄前体卵黄蛋白的血浆水平较低；也就是说，它们的生殖“准备”较低。这些数据支持这样的假设，即 Eudyptes 企鹅的极端卵大小二态性是由于迁徙代谢效应带来的生理限制造成的，并且反对 A 小卵具有特定的、适应性的功能。
