Merilä J, Sheldon B C, Ellegren H
Laboratory of Ecology and Animal Systematics, Department of Biology, University of Turku, FIN-20014, Turku, Finland.
Institute of Cell, Animal and Population Biology, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JT, United Kingdom.
Evolution. 1998 Jun;52(3):870-876. doi: 10.1111/j.1558-5646.1998.tb03711.x.
Quantitative genetic theory predicts that evolution of sexual size dimorphism (SSD) will be a slow process if the genetic correlation in size between the sexes is close to unity, and the heritability of size is similar in both sexes. However, there are very few reliable estimates of genetic correlations and sex-specific heritabilities from natural populations, the reasons for this being that (1) offspring have often been sexed retrospectively, and hence, selection acting differently with respect to body size in the two sexes between measuring and sex identification can bias estimates of SSD; and (2) in many taxa, parents may be incorrectly assigned to offspring either because of assignment errors or because of extrapair paternity. We used molecular sex and paternity identification to overcome these problems and estimated sex-specific heritabilities and the genetic correlation in body size between the two sexes in the collared flycatcher, Ficedula albicollis. After exclusion of the illegitimate offspring, the genetic correlation in body size between the sexes was 1.00 (SE = 0.22), implying a severe constraint on the evolution of SSD in this species. Furthermore, sex-specific heritability estimates were very similar, indicating that neither sex will be able to evolve faster than the other. By using estimated genetic parameters, together with empirically derived estimates of sex-specific selection gradients, we further demonstrated that the predicted selection response in female tarsus length is displaced about 200% in the opposite direction from that to be expected if there were no genetic correlation between the sexes. The correspondence between the biochemically estimated rate of extrapair paternity (about 15 % of the young) and that estimated from the "heritability method" (11%) was good. However, the estimated rate of extrapair paternity with the heritability method after exclusion of the illegitimate young was 22%, adding to increasing evidence that factors other than extrapair paternity (e.g., maternal effects) may be resposible for the commonly observed higher mother-offspring than father-offspring resemblance.
数量遗传学理论预测，如果两性之间体型的遗传相关性接近1，且两性体型的遗传力相似，那么两性异形（SSD）的进化将是一个缓慢的过程。然而，来自自然种群的遗传相关性和性别特异性遗传力的可靠估计非常少，原因如下：（1）后代通常是事后进行性别鉴定的，因此，在测量和性别鉴定之间，针对两性体型的选择作用不同，这可能会使SSD的估计产生偏差；（2）在许多分类群中，由于分配错误或因为异交父权，父母可能会被错误地与后代配对。我们使用分子性别和父权鉴定来克服这些问题，并估计了白领姬鹟（Ficedula albicollis）两性的性别特异性遗传力以及体型的遗传相关性。排除非婚生后代后，两性体型的遗传相关性为1.00（标准误 = 0.22），这意味着该物种的SSD进化受到严重限制。此外，性别特异性遗传力估计非常相似，表明两性都无法比对方进化得更快。通过使用估计的遗传参数，结合经验得出的性别特异性选择梯度估计，我们进一步证明，雌性跗骨长度的预测选择反应与不存在两性遗传相关性时预期的方向相反，偏移了约200%。生化估计的异交父权率（约占幼鸟的15%）与从“遗传力方法”估计的结果（11%）之间的对应关系良好。然而，排除非婚生幼鸟后，用遗传力方法估计的异交父权率为22%，这进一步证明，除了异交父权（例如母体效应）之外的其他因素可能是导致普遍观察到的母本与后代相似性高于父本与后代相似性的原因。
