Department of Biological Sciences, Lehigh University, Bethlehem, United States.
Elife. 2020 Dec 29;9:e62238. doi: 10.7554/eLife.62238.
A common misconception is that evolution is a linear 'march of progress', where each organism along a line of descent is more fit than all those that came before it. Rejecting this misconception implies that evolution is nontransitive: a series of adaptive events will, on occasion, produce organisms that are less fit compared to a distant ancestor. Here we identify a nontransitive evolutionary sequence in a 1000-generation yeast evolution experiment. We show that nontransitivity arises due to adaptation in the yeast nuclear genome combined with the stepwise deterioration of an intracellular virus, which provides an advantage over viral competitors within host cells. Extending our analysis, we find that nearly half of our ~140 populations experience multilevel selection, fixing adaptive mutations in both the nuclear and viral genomes. Our results provide a mechanistic case-study for the adaptive evolution of nontransitivity due to multilevel selection in a 1000-generation host/virus evolution experiment.
一个常见的误解是，进化是一种线性的“进步的历程”，沿着进化谱系的每一个生物体都比它之前的所有生物体更适应环境。拒绝这种误解意味着进化是非传递的：一系列适应性事件偶尔会产生与遥远祖先相比适应性较低的生物体。在这里，我们在一个持续了 1000 代的酵母进化实验中确定了一个非传递的进化序列。我们表明，非传递性是由于酵母核基因组的适应性进化与一种逐渐恶化的细胞内病毒相结合而产生的，这种病毒在宿主细胞内相对于病毒竞争者具有优势。通过扩展我们的分析，我们发现我们的近一半 (~140 个) 种群经历了多层次选择，在核基因组和病毒基因组中固定了适应性突变。我们的结果为在一个持续了 1000 代的宿主/病毒进化实验中，由于多层次选择而导致非传递性的适应性进化提供了一个机制性的案例研究。
