School of Biological Sciences, The University of Queensland, Brisbane 4072, Australia
Evolution. 2013 Feb;67(2):328-37. doi: 10.1111/j.1558-5646.2012.01749.x. Epub 2012 Aug 22.
Offspring size is one of the most important life-history traits with consequences for both the ecology and evolution of most organisms. Surprisingly, formal estimates of selection on offspring size are rare, and the degree to which selection (particularly nonlinear selection) varies among environments remains poorly explored. We estimate linear and nonlinear selection on offspring size, module size, and senescence rate for a sessile marine invertebrate in the field under three different intensities of interspecific competition. The intensity of competition strongly modified the strength and form of selection acting on offspring size. We found evidence for differences in nonlinear selection across the three environments. Our results suggest that the fitness returns of a given offspring size depend simultaneously on their environmental context, and on the context of other offspring traits. Offspring size effects can be more pervasive with regards to their influence on the fitness returns of other traits than previously recognized, and we suggest that the evolution of offspring size cannot be understood in isolation from other traits. Overall, variability in the form and strength of selection on offspring size in nature may reduce the efficacy of selection on offspring size and maintain variation in this trait.
后代大小是最重要的生活史特征之一，对大多数生物的生态和进化都有影响。令人惊讶的是，对后代大小选择的正式估计很少，而且选择（特别是非线性选择）在环境之间的变化程度仍未得到充分探索。我们在三种不同的种间竞争强度下，对一种固着的海洋无脊椎动物的后代大小、模块大小和衰老率进行了线性和非线性选择的估计。竞争的强度强烈改变了后代大小的选择强度和形式。我们发现了三个环境中非线性选择差异的证据。我们的研究结果表明，特定后代大小的适应度回报不仅取决于其环境背景，还取决于其他后代特征的背景。与以前的认识相比，后代大小对其他特征的适应度回报的影响可能更为普遍，我们认为，后代大小的进化不能与其他特征孤立开来。总的来说，自然界中后代大小选择的形式和强度的可变性可能会降低对后代大小选择的有效性，并维持这种特征的变异性。
