Theoretical Sciences Unit and Evolutionary and Organismal Biology Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560064, India.
Evolution. 2011 Jul;65(7):1945-55. doi: 10.1111/j.1558-5646.2011.01280.x. Epub 2011 Mar 29.
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 loci increases. Our study indicates that an advantage for small populations is likely whenever the fitness landscape contains local maxima. The advantage appears at intermediate time scales, which are long enough for trapping at local fitness maxima to have occurred but too short for peak escape by the creation of multiple mutants.
最近的实验和理论研究表明，在复杂适应度景观上进化的小无性种群可能比大种群具有更高的适应性，因为适应性轨迹的异质性增加了。在这里，我们引入了一类单倍体三基因座适应度景观，可通过精确和定量的方式研究这种情况。我们的主要分析结果表明，选择最大初始适应度增长路径的概率如何随种群规模而增加。这使得大种群更有可能被困在局部适应度峰值处，并意味着在中间时间尺度上小种群具有优势。这种效应起作用的种群规模范围与克隆干扰的开始相吻合。使用随机适应度景观的集合进行的其他研究表明，对于特定的三基因座景观参数选择所获得的结果是稳健的，并且随着基因座数量的增加而持续存在。我们的研究表明，只要适应度景观包含局部最大值，小种群就具有优势。这种优势出现在中间时间尺度上，这些时间尺度足够长，足以发生在局部适应度最大值处的捕获，但不足以通过创建多个突变体来逃脱峰值。
