Edward Grey Institute, Department of Zoology, University of Oxford, Oxford, OX1 3SZ, UK.
Centre for Ecology and Conservation, University of Exeter, Penryn, TR10 9FE, UK.
Evolution. 2020 Oct;74(10):2320-2331. doi: 10.1111/evo.13980. Epub 2020 May 10.
Within-population variation in the traits underpinning reproductive output has long been of central interest to biologists. Since they are strongly linked to lifetime reproductive success, these traits are expected to be subject to strong selection and, if heritable, to evolve. Despite the formation of durable pair bonds in many animal taxa, reproductive traits are often regarded as female-specific, and estimates of quantitative genetic variation seldom consider a potential role for heritable male effects. Yet reliable estimates of such social genetic effects are important since they influence the amount of heritable variation available to selection. Based on a 52-year study of a nestbox-breeding great tit (Parus major) population, we apply "extended" bivariate animal models in which the heritable effects of both sexes are modeled to assess the extent to which males contribute to heritable variation in seasonal reproductive timing (egg laying date) and clutch size, while accommodating the covariance between the two traits. Our analyses show that reproductive timing is a jointly expressed trait in this species, with (positively covarying) heritable variation for laydate being expressed in both members of a breeding pair, such that the total heritable variance is 50% larger than estimated by traditional models. This result was robust to explicit consideration of a potential male-biased environmental confound arising through sexually dimorphic dispersal. In contrast to laydate, males' contribution to heritable variation in clutch size was limited. Our study thus highlights the contrasting extent of social determination for two major components of annual reproductive success, and emphasizes the need to consider the social context of what are often considered individual-level traits.
长期以来，生物学家一直对生殖输出基础的性状在种群内的变异感兴趣。由于这些性状与终生生殖成功密切相关，因此预计它们将受到强烈的选择作用，如果可遗传，它们将进化。尽管许多动物类群形成了持久的配对关系，但生殖性状通常被认为是雌性特有的，并且对数量遗传变异的估计很少考虑到可遗传的雄性效应的潜在作用。然而，由于这些社会遗传效应会影响可供选择的可遗传变异量，因此可靠地估计这些效应非常重要。基于对一个巢箱繁殖的大山雀（Parus major）种群进行的 52 年研究，我们应用了“扩展”双变量动物模型，其中对两性的可遗传效应进行建模，以评估雄性对季节性生殖时间（产卵日期）和卵窝大小的可遗传变异的贡献程度，同时适应这两个性状之间的协方差。我们的分析表明，在这个物种中，生殖时间是一个共同表达的性状，具有（正协变）产卵日期的可遗传变异在繁殖对的两个成员中都有表达，使得总可遗传方差比传统模型估计的大 50%。这一结果对通过性二态扩散产生的潜在雄性偏向环境混杂的明确考虑是稳健的。与产卵日期相反，雄性对卵窝大小的可遗传变异的贡献有限。因此，我们的研究突出了年度生殖成功的两个主要组成部分的社会决定程度的对比，强调了需要考虑通常被认为是个体水平特征的社会背景。
