Data from: Spatial heterogeneity in the strength of selection against deleterious alleles and the mutation load

According to current estimates of genomic deleterious mutation rates (which are often of the order 0.1 - 1) the mutation load (defined as a reduction in the average fitness of a population due to the presence of deleterious alleles) may be important in many populations. In this paper, I use multilocus simulations to explore the effect of spatial heterogeneity in the strength of selection against deleterious alleles on the mutation load (for example, it has been suggested that stressful environments may increase the strength of selection). These simulations show contrasted results: in some situations, spatial heterogeneity may greatly reduce the mutation load, due to the fact that migrants coming from demes under stronger selection carry relatively few deleterious alleles, and benefit from a strong advantage within demes under weaker selection (where individuals carry many more deleterious alleles); in other situations, however, deleterious alleles accumulate within demes under stronger selection, due to migration pressure from demes under weaker selection, leading to fitness erosion within those demes. This second situation is more frequent when the productivity of the different demes is proportional to their mean fitness. The effect of spatial heterogeneity is greatly reduced, however, when the response to environmental differences is inconsistent across loci.

根据当前对基因组有害突变率（通常处于0.1~1的量级）的估算，突变负荷（定义为有害等位基因存在导致种群平均适合度下降的程度）在诸多种群中具有重要影响。本文采用多位点模拟方法，探究有害等位基因的选择强度空间异质性对突变负荷的影响——例如，已有研究提出胁迫环境可能增强对有害等位基因的选择强度。本次模拟得到了两类截然不同的结果：在部分情境下，空间异质性可大幅降低突变负荷，其机制为来自选择强度更高的同类群的迁移个体携带的有害等位基因相对较少，因而在有害等位基因更为富集的低选择强度同类群中可获得显著的生存优势；而在另一部分情境中，来自低选择强度同类群的迁移压力会导致高选择强度同类群内有害等位基因积累，进而引发这些同类群的适合度侵蚀。当不同同类群的生产力与其平均适合度成正比时，第二种情境更为常见。不过，当不同位点对环境差异的响应存在不一致时，空间异质性的影响会大幅减弱。