Evolutionary advantage of small populations on complex fitness landscapes

Recent experimental and theoretical studies have shown that small asexual populations evolving on complex fitness landscapes may achieve a higher fitness than large ones due to the increased heterogeneity of adaptive trajectories. Here we introduce a class of haploid three-locus fitness landscapes that allow the investigation of this scenario in a precise and quantitative way. Our main result derived analytically shows how the probability of choosing the path of the largest initial fitness increase grows with the population size. This makes large populations more likely to get trapped at local fitness peaks and implies an advantage of small populations at intermediate time scales. The range of population sizes where this effect is operative coincides with the onset of clonal interference. Additional studies using ensembles of random fitness landscapes show that the results achieved for a particular choice of three-locus landscape parameters are robust and also persist as the number of l...近期的实验与理论研究表明，在复杂适应度景观（fitness landscape）上演化的小型无性繁殖种群，其适应度水平反而可能高于大型种群——这一现象源于适应性轨迹（adaptive trajectory）异质性的提升。本研究引入一类单倍体三座位适应度景观（haploid three-locus fitness landscape），使得我们能够以精准且定量的方式探究这一演化场景。我们通过解析推导得到的核心结果揭示了：选择初始适应度增幅最大的演化路径的概率，如何随种群规模的变化而增长。这使得大型种群更易陷入局部适应度峰（local fitness peak）的演化陷阱，同时也意味着在中等时间尺度下小型种群具备演化优势。该效应发挥作用的种群规模区间，恰好与克隆干扰（clonal interference）的发生阶段相吻合。借助随机适应度景观集合开展的补充研究表明，针对特定三座位景观参数设置得到的研究结果具备稳健性，且随着位点数量（l...，原文未完整给出）增加时该结论依然成立。