Social genes are selection hotspots in kin groups of a soil microbe

The composition of cooperative systems, including animal societies, organismal bodies, and microbial groups, reflects their past and shapes their future evolution. However, genomic diversity within many multiunit systems remains uncharacterized, limiting our ability to understand and compare their evolutionary character. We have analyzed genomic and social-phenotype variation among 120 natural isolates of the cooperative bacterium Myxococcus xanthus derived from six multicellular fruiting bodies. Each fruiting body was composed of multiple lineages radiating from a unique recent ancestor. Genomic evolution was concentrated in selection hotspots associated with evolutionary change in social phenotypes. Synonymous mutations indicated that kin lineages within the same fruiting body often first diverged from a common ancestor more than 100 generations ago. Thus, selection appears to promote endemic diversification of kin lineages that remain together over long histories of local interaction...包括动物社会、有机体个体以及微生物类群在内的合作系统的组成特征，既承载了其过往的演化历程，也塑造了其未来的进化走向。然而，当前诸多多单元合作系统内部的基因组多样性仍未得到系统解析，这极大限制了我们对其演化特征的理解与比较研究。我们针对源自6个多细胞子实体（fruiting body）的120株天然分离的合作性细菌——黄色粘球菌（Myxococcus xanthus）的基因组与社会表型变异展开了分析。每个子实体均由源自一个独特近代共同祖先的多个演化支系所构成。研究发现，基因组演化集中于与社会表型进化改变相关的选择热点区域。同义突变分析结果显示，同一子实体内部的亲缘支系通常早在100余代前便已从共同祖先中分化而来。由此可见，选择作用似乎推动了亲缘支系的地方性多样化，这些支系在长期的局部互作历史中始终保持共存。