Section of Evolutionary Biology, Department Biology II, University of Munich (LMU), Planegg-Martinsried, Germany.
Heredity (Edinb). 2011 Sep;107(3):189-99. doi: 10.1038/hdy.2010.175. Epub 2011 Jan 19.
A key issue in evolutionary biology is an improved understanding of the genetic mechanisms by which species adapt to various environments. Using DNA sequence data, it is possible to quantify the number of adaptive and deleterious mutations, and the distribution of fitness effects of new mutations (its mean and variance) by simultaneously taking into account the demography of a given species. We investigated how selection functions at eight housekeeping genes of four closely related, outcrossing species of wild tomatoes that are native to diverse environments in western South America (Solanum arcanum, S. chilense, S. habrochaites and S. peruvianum). We found little evidence for adaptive mutations but pervasive evidence for strong purifying selection in coding regions of the four species. In contrast, the strength of purifying selection seems to vary among the four species in non-coding (NC) regions (introns). Using F(ST)-based measures of fixation in subdivided populations, we suggest that weak purifying selection has affected the NC regions of S. habrochaites, S. chilense and S. peruvianum. In contrast, NC regions in S. arcanum show a distribution of fitness effects with mutations being either nearly neutral or very strongly deleterious. These results suggest that closely related species with similar genetic backgrounds but experiencing contrasting environments differ in the variance of deleterious fitness effects.
进化生物学中的一个关键问题是，要更好地理解物种适应各种环境的遗传机制。利用 DNA 序列数据，可以通过同时考虑给定物种的人口统计学，量化适应性和有害突变的数量，以及新突变的适应度效应的分布（其均值和方差）。我们研究了在来自南美洲西部不同环境的四个近缘、异交野生番茄物种（Solanum arcanum、S. chilense、S. habrochaites 和 S. peruvianum）的八个管家基因中，选择函数是如何作用的。我们几乎没有发现适应性突变的证据，但在四个物种的编码区都有强烈的净化选择的证据。相比之下，在非编码区（内含子）中，四个物种之间的净化选择强度似乎存在差异。利用基于 F(ST)的分群固定措施，我们认为，弱净化选择影响了 S. habrochaites、S. chilense 和 S. peruvianum 的非编码区。相比之下，S. arcanum 的非编码区的适应度效应分布显示，突变要么几乎是中性的，要么是非常有害的。这些结果表明，具有相似遗传背景但经历不同环境的近缘物种在有害适应度效应的方差上存在差异。
