Selection biases the prevalence and type of epistasis along adaptive trajectories

The contribution to an organism's phenotype from one genetic locus may depend upon the status of other loci. Such epistatic interactions among loci are now recognized as fundamental to shaping the process of adaptation in evolving populations. Although little is known about the structure of epistasis in most organisms, recent experiments with bacterial populations have concluded that antagonistic interactions abound and tend to de-accelerate the pace of adaptation over time. Here, we use the NK model of fitness landscapes to examine how natural selection biases the mutations that substitute during evolution based on their epistatic interactions. We find that, even when beneficial mutations are rare, these biases are strong and change substantially throughout the course of adaptation. In particular, epistasis is less prevalent than the neutral expectation early in adaptation and much more prevalent later, with a concomitant shift from predominantly antagonistic interactions early in adap...

单个遗传位点（genetic locus）对生物体表型的贡献，可能依赖于其他位点的状态。这类位点间的上位性（epistasis）互作，如今被认为是塑造进化种群适应过程的核心机制。尽管目前对多数生物体的上位性结构仍知之甚少，但近期针对细菌种群的实验研究表明，拮抗型上位性互作广泛存在，且往往会随时间推移减缓适应的速率。本研究借助适应度景观（fitness landscape）的NK模型，探究自然选择如何依据突变间的上位性互作，对进化过程中固定的突变施加选择偏倚。研究发现，即便有益突变十分稀缺，这类选择偏倚依然显著，且在整个适应过程中会发生显著变化。具体而言，在适应早期，上位性的发生频率低于中性预期；而在适应后期，其发生频率则显著更高，同时互作类型也从早期以拮抗型为主发生转变……