Data from: Environmental stress does not increase the mean strength of selection

<b>Abstract</b><br/>A common intuition among evolutionary biologists and ecologists is that environmental stress will increase the strength of selection against deleterious alleles and among alternate genotypes. However, the strength of selection is determined by the relative fitness differences among genotypes, and there is no theoretical reason why these differences should be exaggerated as mean fitness decreases. We update a recent review of the empirical results pertaining to environmental stress and the strength of selection and find that there is no overall trend towards increased selection under stress. The majority of past studies measure the strength of selection by quantifying the decrease in fitness imposed by single or multiple mutations in different environments. However, selection rarely acts on one locus independently, and the strength of selection will be determined by variation across the whole genome. We used 20 inbred lines of Drosophila melanogaster to make repeated fitness measurements of the same genotypes in four different environments. This framework allowed us to determine the variation in fitness attributable to genotype across stressful environments and to calculate the opportunity for selection among these genotypes in each stress. While we found significant decreases in mean fitness in our stressful environments, we did not find any significant differences in the strength of selection among any of the four measured environments. Therefore, in agreement with our updated review, we find no evidence for the oft-cited verbal model that stress increases the strength of selection.

【摘要】
进化生物学家与生态学家普遍持有一项直觉认知：环境胁迫会增强针对有害等位基因的选择强度，以及不同基因型之间的选择作用强度。然而，选择强度由各基因型间的相对适合度差异所决定，并无理论依据表明随着平均适合度降低，这类差异会被放大。我们更新了一篇近期关于环境胁迫与选择强度相关实证结果的综述，研究发现胁迫环境下选择强度并未呈现整体上升的趋势。既往多数研究通过量化单一或多重突变在不同环境下对适合度造成的衰减，来衡量选择强度。但选择极少独立作用于单个基因座，其强度将由全基因组的变异情况共同决定。我们使用20个黑腹果蝇（Drosophila melanogaster）近交系，对四种不同环境下的同一基因型开展了重复适合度测定。该实验框架使我们得以明确不同胁迫环境中由基因型带来的适合度变异，并计算出每种胁迫环境下这些基因型间的选择机会。尽管我们在胁迫环境中观测到平均适合度出现显著下降，但并未在四种被测环境中发现选择强度存在显著差异。因此，与我们更新后的综述结论一致，我们未发现支持常被引用的"环境胁迫会增强选择强度"这一文字模型的证据。