Department of Biology, San Francisco State University, San Francisco, CA 94132, USA.
Department of Ecology and Evolutionary Biology, Yale University,New Haven, CT 06520, USA.
G3 (Bethesda). 2022 Aug 25;12(9). doi: 10.1093/g3journal/jkac190.
The dynamics of adaptation, reversion, and compensation have been central topics in microbial evolution, and several studies have attempted to resolve the population genetics underlying how these dynamics occur. However, questions remain regarding how certain features-the evolution of mutators and whether compensatory mutations alleviate costs fully or partially-may influence the evolutionary dynamics of compensation and reversion. In this study, we attempt to explain findings from experimental evolution by utilizing computational and theoretical approaches toward a more refined understanding of how mutation rate and the fitness effects of compensatory mutations influence adaptive dynamics. We find that high mutation rates increase the probability of reversion toward the wild type when compensation is only partial. However, the existence of even a single fully compensatory mutation is associated with a dramatically decreased probability of reversion to the wild type. These findings help to explain specific results from experimental evolution, where compensation was observed in nonmutator strains, but reversion (sometimes with compensation) was observed in mutator strains, indicating that real-world compensatory mutations are often unable to fully alleviate the costs associated with adaptation. Our findings emphasize the potential role of the supply and quality of mutations in crafting the dynamics of adaptation and reversal, with implications for theoretical population genetics and for biomedical contexts like the evolution of antibiotic resistance.
适应、回复和补偿的动态一直是微生物进化的核心议题，已有多项研究试图解决这些动态发生的群体遗传学基础。然而，某些特征（突变体的进化，以及补偿突变是否完全或部分减轻成本）如何影响补偿和回复的进化动态，仍存在疑问。在这项研究中，我们试图通过计算和理论方法来解释实验进化中的发现，以更深入地了解突变率和补偿突变的适应效应如何影响适应动态。我们发现，当补偿不完全时，高突变率会增加回复到野生型的概率。然而，即使只有一个完全补偿的突变，也会导致回复到野生型的概率显著降低。这些发现有助于解释实验进化中的具体结果，即在非突变体菌株中观察到补偿，但在突变体菌株中观察到回复（有时伴有补偿），表明现实世界中的补偿突变通常无法完全减轻适应相关的成本。我们的发现强调了突变的供应和质量在塑造适应和回复动态方面的潜在作用，这对理论群体遗传学以及抗生素耐药性等生物医学背景具有重要意义。
