Parallel emergence of negative epistasis across experimental lineages

Epistatic interactions can greatly impact evolutionary phenomena, particularly the process of adaptation. Here, we leverage four parallel experimentally evolved lineages to study the emergence and trajectories of epistatic interactions in the social bacterium Myxococcus xanthus. A social gene (pilA) necessary for effective group swarming on soft agar had been deleted from the common ancestor of these lineages. During selection for competitiveness at the leading edge of growing colonies, two lineages evolved qualitatively novel mechanisms for greatly increased swarming on soft agar, whereas the other two lineages evolved relatively small increases in swarming. By reintroducing pilA into different genetic backgrounds along the four lineages, we tested whether parallel lineages showed similar patterns of epistasis. In particular, we tested whether a pattern of negative epistasis between accumulating mutations and pilA previously found in the fastest lineage would be found only in the two e...上位性互作（epistatic interactions）可对进化现象，尤其是适应过程，产生显著影响。本研究利用四个平行实验进化谱系，探究社交细菌黄色粘球菌（Myxococcus xanthus）内上位性互作的出现与演化轨迹。该谱系的共同祖先已缺失了介导软琼脂培养基上高效群体集群运动的社交基因pilA。在针对生长菌落前沿区域的竞争能力开展选择实验时，两个谱系演化出了质上全新的机制，可大幅提升软琼脂培养基上的集群运动能力；而另外两个谱系的集群运动能力仅出现相对小幅提升。我们通过将pilA基因重新引入四个谱系的不同遗传背景中，验证了平行进化谱系是否呈现出相似的上位性模式。具体而言，我们验证了此前在最快演化谱系中发现的、累积突变与pilA之间的负上位性模式，是否仅存在于两个……