Data from: Benefit of transferred mutations is better predicted by the fitness of recipients than by their ecological or genetic relatedness

The effect of a mutation depends on its interaction with the genetic background in which it is assessed. Studies in experimental systems have demonstrated that such interactions are common among beneficial mutations and often follow a pattern consistent with declining evolvability of more fit genotypes. However, these studies generally examine the consequences of interactions between a small number of focal mutations. It is not clear, therefore, that findings can be extrapolated to natural populations, where new mutations may be transferred between genetically divergent backgrounds. We build on work that examined interactions between four beneficial mutations selected in a laboratory-evolved population of Escherichia coli to test how they interact with the genomes of diverse natural isolates of the same species. We find that the fitness effect of transferred mutations depends weakly on the genetic and ecological similarity of recipient strains relative to the donor strain in which the mutations were selected. By contrast, mutation effects were strongly inversely correlated to the initial fitness of the recipient strain. That is, there was a pattern of diminishing returns whereby fit strains benefited proportionally less from an added mutation. Our results strengthen the view that the fitness of a strain can be a major determinant of its ability to adapt. They also support a role for barriers of transmission, rather than differential selection of transferred DNA, as an explanation of observed phylogenetically determined patterns of restricted recombination among E. coli strains.

突变的效应取决于其与自身被评估时所处的遗传背景（genetic background）之间的互作。基于实验体系的研究表明，这类互作在有益突变（beneficial mutations）中十分常见，且通常呈现出与高适合度基因型（fit genotypes）的演化能力（evolvability）下降相符的模式。然而，此类研究大多仅考察少量目标突变间的互作效应，因此目前尚不清楚这些结论能否外推至自然种群——在自然种群中，新突变可在遗传背景存在差异的个体间发生转移。本研究依托一项已有工作：该工作针对实验室演化的大肠杆菌（Escherichia coli）种群中筛选出的4种有益突变之间的互作展开分析，本研究则以此为基础，检验这些突变与同一物种不同自然分离株的基因组之间的互作模式。研究结果显示，转移后的突变的适合度效应，仅与受体菌株相对于突变筛选所用供体菌株的遗传与生态相似性呈弱相关。与之形成鲜明对比的是，突变效应与受体菌株的初始适合度呈显著负相关，即呈现出报酬递减的模式：高适合度菌株从新增突变中获得的收益比例更低。本研究结果进一步强化了“菌株的适合度是其适应能力的核心决定因素”这一观点，同时也支持以传播障碍而非转移DNA的差异化选择，来解释已观测到的大肠杆菌菌株间由系统发育决定的限制性重组模式。