Williams T D, Lank D B, Cooke F, Rockwell R F
Department of Animal & Plant Sciences, University of Sheffield, PO Box 601, S10 2UQ, Sheffield, UK.
Department of Biology, Queen's University, K7L 3N6, Kingston, Ontario, Canada.
Oecologia. 1993 Dec;96(3):331-338. doi: 10.1007/BF00317502.
We investigated the relationship between eggsize variation and (a) egg hatching success, (b) chick survival to fledging and recruitment, and (c) adult female survival, over 12 years in the lesser snow goose (Anser caerulescens caerulescens). By comparing the means and variances of egg size for successful and unsuccessful eggs, our aim was to assess the relative fitness of eggs of different sizes and to determine the type of selection operating on egg size in this species. As both egg size and reproductive success vary with age in the lesser snow goose we controlled for the effects of female age. Egg-size variation is very marked in this population, varying by up to 52% for eggs hatching successfully. However, there was no relationship between egg size and post-hatching survival of goslings to fledging or recruitment, either within or between broods, pooling across years. Egg size varied significantly between successful and unsuccessful clutches in only 2 of 33 individual year comparisons. First-laid eggs surviving to onset of incubation, and eggs hatching successfully, were on average larger than unsuccessful eggs, but this was probably due to the confounding effects of female age-specific and sequence-specific egg survival. Variance of egg size differed significantly between successful and unsuccessful eggs in only 3 of 24, and 0 of 21, individual year comparisons for pre- and post-hatching survival respectively. We therefore found little evidence for a relationship between egg-size variation and offspring fitness, or for strong directional, normalising or diversifying selection operating on egg size, in the lesser snow goose. In addition, there was only weak support for the hypothesis that egg-size variation is maintained by temporal variation in selection pressure (sensu Ankney and Bisset 1973). It is likely that egg-size variation represents the pleiotropic expression of alleles affecting more general physiological or metabolic processes. While this does not rule out the existence of alleles with more direct effects on egg size we suggest that their contribution to heritable egg size is small.
我们对小雪雁（Anser caerulescens caerulescens）12年间的蛋大小变化与（a）蛋孵化成功率、（b）雏鸟存活至羽翼丰满和补充数量，以及（c）成年雌鸟存活情况之间的关系进行了研究。通过比较成功孵化和未成功孵化的蛋的大小均值和方差，我们的目的是评估不同大小的蛋的相对适合度，并确定该物种中作用于蛋大小的选择类型。由于小雪雁的蛋大小和繁殖成功率都随年龄变化，我们控制了雌鸟年龄的影响。该种群中蛋大小的变化非常显著，成功孵化的蛋大小差异高达52%。然而，无论是在窝内还是窝间，合并多年的数据来看，蛋大小与雏鹅孵化后存活至羽翼丰满或补充数量之间均无关系。在33个单独年份的比较中，只有2年成功孵化和未成功孵化的窝之间蛋大小存在显著差异。成功孵化至孵化开始的首枚蛋以及成功孵化的蛋平均比未成功孵化的蛋大，但这可能是由于雌鸟年龄特异性和顺序特异性的蛋存活的混杂效应。在分别针对孵化前和孵化后存活情况的24个和21个单独年份比较中，成功孵化和未成功孵化的蛋的大小方差仅在3个和0个比较中存在显著差异。因此，我们几乎没有发现证据表明蛋大小变化与后代适合度之间存在关系，也没有发现对蛋大小有强烈的定向、正态化或多样化选择作用于该物种的证据。此外，对于蛋大小变化是由选择压力的时间变化所维持这一假设（参照安克尼和比塞特1973年的研究），仅有微弱的支持。蛋大小变化很可能代表了影响更一般生理或代谢过程的等位基因的多效性表达。虽然这并不排除存在对蛋大小有更直接影响的等位基因，但我们认为它们对可遗传蛋大小的贡献很小。
