Department of Biology, Carleton University, Ottawa, ON, Canada.
Great Ormond Street Institute of Child Health, University College London, London, United Kingdom.
Evolution. 2024 Feb 29;78(3):566-578. doi: 10.1093/evolut/qpad189.
Genetic background has the potential to influence both the tempo and trajectory of adaptive change: Different genotypes of a given species may adopt varied solutions to the same environmental challenge, or they may approach the same solution at different rates. Laboratory selection has been widely used to experimentally examine the evolutionary consequences of variation in genetic background, although largely using genotypes differing by only a few mutations. Here, we leverage natural variation in the bacterium Pseudomonas aeruginosa to investigate whether different adaptive solutions are accessible from distant points of departure on an adaptive landscape. We evolved 17 diverse genotypes in a laboratory medium that partially mimics the lung sputum of cystic fibrosis patients, and we measured changes in 10 phenotypes as well as in fitness. Using phylogenetically informed analyses, we found that genetic background impacted the tempo, but not the trajectory, of phenotypic evolution: Different starting genotypes converged toward similar phenotypes, but at varying rates. Our findings add to a growing body of evidence supporting widespread diminishing return epistasis during adaptation. The importance of genetic background toward the trajectory of adaptation remains inconsistent across experimental systems and conditions.
同一物种的不同基因型可能会采用不同的方法来应对相同的环境挑战，或者它们可能会以不同的速度接近相同的解决方案。实验室选择已被广泛用于实验性地研究遗传背景变异的进化后果，尽管主要使用的是仅相差几个突变的基因型。在这里，我们利用细菌铜绿假单胞菌中的自然变异来研究在适应性景观上的不同起始点是否可以获得不同的适应性解决方案。我们在部分模拟囊性纤维化患者肺部痰液的实验室培养基中进化了 17 个不同的基因型，并测量了 10 种表型和适应性的变化。使用系统发育信息分析，我们发现遗传背景影响了表型进化的速度，但不影响轨迹：不同的起始基因型向相似的表型收敛，但速度不同。我们的研究结果增加了越来越多的证据，支持适应性过程中广泛存在的回报递减上位性。遗传背景对适应轨迹的重要性在不同的实验系统和条件下仍然不一致。
