Data from: A framework for estimating the fixation time of an advantageous allele in stepping-stone models

Determining how population subdivision increases the fixation time of an advantageous allele is an important problem in evolutionary genetics as this influences many processes. Here, I lay out a framework for calculating the fixation time of a positively selected allele in a subdivided population, as a function of the number of demes present, the migration rate between them, and the manner in which they are connected. Using this framework it becomes clear that a beneficial allele's fixation time is significantly reduced through migration continuously introducing copies of the allele into a newly-colonised subpopulation, increasing its frequency within these demes. The effect that migration has on allele frequency needs to be explicitly taken into account to produce a realistic estimate of fixation time. This behaviour is most prominent when demes are arranged on a two-dimensional torus, in comparison to populations where demes are arranged in a circle. This is because each subpopulation is connected to several neighbours over a torus, so that there are multiple paths that an allele can take in order to fix. As a consequence, some demes experience a greater influx and efflux of migrants than others. Analytical results are found to be very accurate when compared to stochastic simulations, and are generally robust if there are a large number of demes, or if the allele is weakly selected for.

探究种群细分（population subdivision）如何延长有利等位基因（advantageous allele）的固定时间（fixation time），是进化遗传学领域的重要课题——该过程对诸多演化进程均具有关键影响。本文构建了一套用于计算细分种群中受正向选择等位基因固定时间的理论框架，将固定时间表示为现有同类群（demes）数量、同类群间迁移率以及同类群连接方式的函数。借助该框架可明确：迁移会持续将有利等位基因的拷贝引入新定殖的亚种群，提升这些同类群内的等位基因频率，进而显著缩短有利等位基因的固定时间。若要获得符合实际的固定时间估算结果，必须明确考量迁移对等位基因频率的影响。相较于同类群呈环形排布的种群，当同类群以二维环面（two-dimensional torus）形式排布时，上述效应表现得最为显著。这是由于在环面结构中，每个亚种群都与多个邻近同类群相连，因此等位基因可通过多条路径完成固定。由此，部分同类群的迁移个体流入与流出量高于其余同类群。经与随机模拟（stochastic simulations）对比验证，本文所得解析结果准确度极高；且当同类群数量较多，或等位基因受弱正向选择时，该解析结果整体具备稳健性。