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.

突变间的上位性互作在进化论研究中占据核心地位。诸多研究已证实上位性广泛存在，但此类探索极少关注有益突变。本研究针对大肠杆菌（Escherichia coli）实验种群中首批固定的五个突变，分析了上位性对适合度的影响。结果显示，上位性效应与组合突变的整体效应密切相关：预期获益越大，上位性效应的负向程度越强。尽管涉及某一特定突变的互作呈现出相反效应，但整体而言上位性会随基因型适合度提升呈现收益递减的特征。本研究数据支持“负向上位性会随时间推移降低适应性进化速率”的理论模型。相较于此前单基因突变研究中符号上位性（sign epistasis）普遍存在的情况，本全基因组研究中的符号上位性极为罕见。