Data from: Evolution of drift robustness in small populations

Most mutations are deleterious and cause a reduction in population fitness known as the mutational load. In small populations, weakened selection against slightly-deleterious mutations results in an additional fitness reduction. Many studies have established that populations can evolve a reduced mutational load by evolving mutational robustness, but it is uncertain whether small populations can evolve a reduced susceptibility to drift-related fitness declines. Here, using mathematical modeling and digital experimental evolution, we show that small populations do evolve a reduced vulnerability to drift, or ‘drift robustness’. We find that, compared to genotypes from large populations, genotypes from small populations have a decreased likelihood of small-effect deleterious mutations, thus causing small-population genotypes to be drift-robust. We further show that drift robustness is not adaptive, but instead arises because small populations can only maintain fitness on drift-robust fitness peaks. These results have implications for genome evolution in organisms with small effective population sizes.绝大多数突变均为有害突变，会导致种群适合度下降，这一现象被称为突变负荷（mutational load）。在小型种群中，对轻微有害突变的选择作用减弱，会进一步加剧适合度的下降。多项研究已证实，种群可通过演化获得突变鲁棒性（mutational robustness）以降低突变负荷，但目前尚不明确小型种群能否演化出对漂变相关适合度下降的更低易感性。本研究借助数学建模与数字化实验演化手段，证实小型种群确实能够演化出对漂变的更低易感性，即‘漂变鲁棒性（drift robustness）’。研究发现，与大型种群的基因型相比，小型种群的基因型出现小效应有害突变的概率更低，这正是小型种群基因型具备漂变鲁棒性的原因。本研究进一步证实，漂变鲁棒性并非适应性演化的结果，而是源于小型种群仅能在具备漂变鲁棒性的适合度峰上维持适合度。上述研究结果对有效种群规模较小的生物的基因组演化具有参考意义。