Behavior, Ecology, Evolution, and Systematics Section, School of Biological Sciences, Illinois State University, Normal, 61790, USA.
Am Nat. 2011 May;177(5):617-29. doi: 10.1086/659630.
Increased variance in the reproductive success of males relative to females favors mothers that optimally allocate sons and daughters to maximize their fitness return. In altricial songbirds, one influence on the fitness prospects of offspring arises through the order in which nestlings hatch from their eggs, which affects individual mass and size before nest leaving. In house wrens (Troglodytes aedon), the influence of hatching order depends on the degree of hatching synchrony, with greater variation in nestling mass and size within broods hatching asynchronously than in those hatching synchronously. Early-hatching nestlings in asynchronous broods were heavier and larger than their later-hatching siblings and nestlings in synchronous broods. The effect of hatching order was also sex specific, as the mass of males in asynchronous broods was more strongly influenced by hatching order than the mass of females, with increased variation in the mass of males relative to that of females. As predicted, mothers hatching their eggs asynchronously biased first-laid, first-hatching eggs toward sons and late-laid, late-hatching eggs toward daughters, whereas females hatching their eggs synchronously distributed the sexes randomly among the eggs of their clutch. We conclude that females allocate the sex of their offspring among the eggs of their clutch in a manner that maximizes their own fitness.
与雌性相比，雄性繁殖成功率的变异性增加，有利于母亲通过最佳分配儿子和女儿来最大化其适应度回报。在晚成性鸣禽中，影响后代适应度前景的一个因素是雏鸟从蛋中孵化的顺序，这会影响离巢前个体的体重和大小。在穴居鹪鹩（Troglodytes aedon）中，孵化顺序的影响取决于孵化同步的程度，在孵化不同步的巢中，雏鸟的体重和大小变化比孵化同步的巢中更大。在孵化不同步的巢中，早孵化的雏鸟比晚孵化的雏鸟兄弟姐妹和孵化同步的巢中的雏鸟更重更大。孵化顺序的影响也具有性别特异性，因为在孵化不同步的巢中，雄性雏鸟的体重受孵化顺序的影响比雌性雏鸟更大，雄性雏鸟的体重变化相对于雌性雏鸟更大。正如预测的那样，孵化不同步的母亲会将第一批产卵、最早孵化的卵偏向雄性，将晚产、晚孵化的卵偏向雌性，而孵化同步的雌性则会在其产卵的巢中随机分配性别。我们得出的结论是，雌性通过一种方式在其产卵的巢中分配后代的性别，以最大化其自身的适应度。
