Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109.
Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Kashiwa, Chiba Prefecture 277-8562, Japan.
Proc Natl Acad Sci U S A. 2017 Nov 14;114(46):12219-12224. doi: 10.1073/pnas.1710351114. Epub 2017 Oct 31.
Although evolution by natural selection is widely regarded as the most important principle of biology, it is unknown whether phenotypic variations within and between species are mostly adaptive or neutral due to the lack of relevant studies of large, unbiased samples of phenotypic traits. Here, we examine 210 yeast morphological traits chosen because of experimental feasibility irrespective of their potential adaptive values. Our analysis is based on the premise that, under neutrality, the rate of phenotypic evolution measured in the unit of mutational size declines as the trait becomes more important to fitness, analogous to the neutral paradigm that functional genes evolve more slowly than functionless pseudogenes. However, we find faster evolution of more important morphological traits within and between species, rejecting the neutral hypothesis. By contrast, an analysis of 3,466 gene expression traits fails to refute neutrality. Thus, at least in yeast, morphological evolution appears largely adaptive, but the same may not apply to other classes of phenotypes. Our neutrality test is applicable to other species, especially genetic model organisms, for which estimations of mutational size and trait importance are relatively straightforward.
尽管自然选择进化被广泛认为是生物学中最重要的原则，但由于缺乏对大的、无偏样本的表型特征的相关研究，仍然不清楚物种内和物种间的表型变异主要是适应性的还是中性的。在这里，我们研究了 210 种酵母形态特征，之所以选择这些特征，是因为它们具有实验可行性，而不论其潜在的适应性价值如何。我们的分析基于以下前提：在中性条件下，在单位突变大小下测量的表型进化速度随着特征对适应性的重要性的增加而下降，类似于功能基因比无功能假基因进化得更慢的中性范例。然而，我们发现物种内和物种间更重要的形态特征的进化速度更快，从而否定了中性假设。相比之下，对 3466 个基因表达特征的分析并没有反驳中性。因此，至少在酵母中，形态进化似乎主要是适应性的，但其他类别的表型可能并非如此。我们的中性检验适用于其他物种，特别是遗传模式生物，因为它们的突变大小和特征重要性的估计相对简单。
