Data from: Negative epistasis between beneficial mutations in an evolving bacterial population

Epistatic interactions between mutations play a prominent role in evolutionary theories. Many studies have found that epistasis is widespread, but they have rarely considered beneficial mutations. We analyzed the effects of epistasis on fitness for the first five mutations to fix in an experimental population of Escherichia coli. Epistasis depended on the effects of the combined mutations—the larger the expected benefit, the more negative the epistatic effect. Epistasis thus tended to produce diminishing returns with genotype fitness, although interactions involving one particular mutation had the opposite effect. These data support models in which negative epistasis contributes to declining rates of adaptation over time. Sign epistasis was rare in this genome-wide study, in contrast to its prevalence in an earlier study of mutations in a single gene.

突变间的上位性（epistasis）相互作用在进化理论中具有核心地位。诸多研究已证实上位性广泛存在，但此类探讨极少关注有益突变。本研究以实验种群大肠杆菌（Escherichia coli）中首批完成固定的五个突变为对象，分析了上位性对适合度（fitness）的影响。上位性的强度与组合突变的联合效应呈显著相关：预期收益越高，其上位性效应的负向程度越强。整体而言，上位性会随基因型适合度提升呈现收益递减效应，但涉及某一特定突变的相互作用则表现出相反趋势。本研究数据支持下述模型：负向上位性会随时间推移导致种群适应速率逐步降低。相较于此前针对单基因突变的研究中符号上位性（sign epistasis）广泛分布的情况，本项全基因组研究内符号上位性极为罕见。