Institute of Ecology and Evolution, University of Bern, Bern, Switzerland.
Swiss Institute for Bioinformatics, Lausanne, Switzerland.
Mol Ecol. 2024 May;33(10):e16900. doi: 10.1111/mec.16900. Epub 2023 Mar 20.
How does standing genetic variation affect polygenic adaptation in recombining populations? Despite a large body of work in quantitative genetics, epistatic and weak additive fitness effects among simultaneously segregating genetic variants are difficult to capture experimentally or to predict theoretically. In this study, we simulated adaptation on fitness landscapes with tunable ruggedness driven by standing genetic variation in recombining populations. We confirmed that recombination hinders the movement of a population through a rugged fitness landscape. When surveying the effect of epistasis on the fixation of alleles, we found that the combined effects of high ruggedness and high recombination probabilities lead to preferential fixation of alleles that had a high initial frequency. This indicates that positive epistatic alleles escape from being broken down by recombination when they start at high frequency. We further extract direct selection coefficients and pairwise epistasis along the adaptive path. When taking the final fixed genotype as the reference genetic background, we observe that, along the adaptive path, beneficial direct selection appears stronger and pairwise epistasis weaker than in the underlying fitness landscape. Quantitatively, the ratio of epistasis and direct selection is smaller along the adaptive path ( ) than expected. Thus, adaptation on a rugged fitness landscape may lead to spurious signals of direct selection generated through epistasis. Our study highlights how the interplay of epistasis and recombination constrains the adaptation of a diverse population to a new environment.
在重组群体中，遗传背景中的固定变异如何影响多基因适应性？尽管在数量遗传学方面已经有大量的研究，但同时分离的遗传变异之间的上位性和弱加性适合度效应很难通过实验来捕捉或通过理论来预测。在本研究中，我们模拟了在由重组群体中的遗传背景中的固定变异驱动的可调节崎岖度的适应景观上的适应性。我们证实了重组阻碍了种群在崎岖的适应景观中的移动。当调查上位性对等位基因固定的影响时，我们发现，高崎岖度和高重组概率的综合效应导致具有高初始频率的等位基因优先固定。这表明，当高频率的有利上位性等位基因开始时，它们会逃避重组的破坏。我们进一步沿着适应路径提取直接选择系数和成对的上位性。当以最终固定的基因型作为参考遗传背景时，我们观察到，沿着适应路径，有利的直接选择比基础适应景观中更强，而成对的上位性则更弱。从数量上看，沿着适应路径的上位性和直接选择的比值（ ）比预期的要小。因此，在崎岖的适应景观上的适应可能会导致通过上位性产生的直接选择的虚假信号。我们的研究强调了上位性和重组的相互作用如何限制了多样化种群对新环境的适应。
