Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
Oecologia. 2014 Mar;174(3):631-8. doi: 10.1007/s00442-013-2803-8. Epub 2013 Oct 15.
Egg components are important mediators of prenatal maternal effects in birds and other oviparous species. Because different egg components can have opposite effects on offspring phenotype, selection is expected to favour their mutual adjustment, resulting in a significant covariation between egg components within and/or among clutches. Here we tested for such correlations between maternally derived yolk immunoglobulins and yolk androgens in great tit (Parus major) eggs using a multivariate mixed-model approach. We found no association between yolk immunoglobulins and yolk androgens within clutches, indicating that within clutches the two egg components are deposited independently. Across clutches, however, there was a significant negative relationship between yolk immunoglobulins and yolk androgens, suggesting that selection has co-adjusted their deposition. Furthermore, an experimental manipulation of ectoparasite load affected patterns of covariance among egg components. Yolk immunoglobulins are known to play an important role in nestling immune defence shortly after hatching, whereas yolk androgens, although having growth-enhancing effects under many environmental conditions, can be immunosuppressive. We therefore speculate that variation in the risk of parasitism may play an important role in shaping optimal egg composition and may lead to the observed pattern of yolk immunoglobulin and yolk androgen deposition across clutches. More generally, our case study exemplifies how multivariate mixed-model methodology presents a flexible tool to not only quantify, but also test patterns of (co)variation across different organisational levels and environments, allowing for powerful hypothesis testing in ecophysiology.
卵成分是鸟类和其他卵生动物产前母体效应的重要介质。由于不同的卵成分可能对后代表型产生相反的影响，因此选择应该有利于它们的相互调节，从而导致卵成分在巢内和/或巢间发生显著的协变。在这里，我们使用多元混合模型方法检验了大山雀（Parus major）卵中母源性蛋黄免疫球蛋白和蛋黄雄激素之间的这种相关性。我们没有发现巢内蛋黄免疫球蛋白和蛋黄雄激素之间存在关联，这表明在巢内，这两种卵成分是独立沉积的。然而，在巢间，蛋黄免疫球蛋白和蛋黄雄激素之间存在显著的负相关关系，这表明选择已经共同调节了它们的沉积。此外，对寄生虫负荷的实验处理影响了卵成分之间协变的模式。已知蛋黄免疫球蛋白在孵化后不久对雏鸟的免疫防御起着重要作用，而蛋黄雄激素虽然在许多环境条件下具有促进生长的作用，但也可能具有免疫抑制作用。因此，我们推测寄生虫风险的变化可能在塑造最佳卵成分方面起着重要作用，并可能导致我们观察到的巢间蛋黄免疫球蛋白和蛋黄雄激素沉积模式。更一般地说，我们的案例研究说明了多元混合模型方法如何不仅提供了一种灵活的工具来量化，而且还可以测试不同组织水平和环境下的（协）变模式，从而在生态生理学中进行强大的假设检验。
