Data from: How species evolve collectively: implications of gene flow and selection for the spread of advantageous alleles

The traditional view that species are held together through gene flow has been challenged by observations that migration is too restricted among populations of many species to prevent local divergence. However, only very low levels of gene flow are necessary to permit the spread of highly advantageous alleles, providing an alternative means by which low-migration species might be held together. We re-evaluate these arguments given the recent and wide availability of indirect estimates of gene flow. Our literature review of Fst values for a broad range of taxa suggests that gene flow in many taxa is considerably greater than suspected from earlier studies and often is sufficiently high to homogenize even neutral alleles. However, there are numerous species from essentially all organismal groups that lack sufficient gene flow to prevent divergence. Crude estimates on the strength of selection on phenotypic traits and effect sizes of quantitative trait loci (QTL) suggest that selection coefficients for leading QTL underlying phenotypic traits may be high enough to permit their rapid spread across populations. Thus, species may evolve collectively at major loci through the spread of favourable alleles, while simultaneously differentiating at other loci due to drift and local selection.传统观点认为物种通过基因流（gene flow）实现种群维系，但诸多观测结果对此提出了挑战：许多物种种群间的基因交流过于受限，无法阻止局部种群分化。然而，仅需极低水平的基因流即可助力高度有利等位基因（allele）的扩散，这为低迁移物种种群的维系提供了另一途径。 鉴于当前基因流间接估算技术已广泛普及，我们重新评估了上述论点。我们针对广泛类群（taxa）的Fst值开展的文献综述显示，许多类群的基因流水平远高于早期研究的推测，且往往足够高，甚至可使中性等位基因实现同质化。然而，几乎所有生物类群中均存在大量物种，其基因流水平不足以阻止种群分化。 针对表型性状的选择强度及数量性状位点（quantitative trait locus, QTL）效应量的粗略估算表明，调控表型性状的关键QTL的选择系数可能足够高，足以使其在种群间快速扩散。因此，物种可通过有利等位基因的扩散在核心位点实现协同进化，同时又可因遗传漂变和局部选择在其他位点发生种群分化。