Data from: Genome-wide differentiation in closely related populations: the roles of selection and geographic isolation

Population divergence in geographic isolation is due to a combination of factors. Natural and sexual selection may be important in shaping patterns of population differentiation, a pattern referred to as ‘Isolation by Adaptation’ (IBA). IBA can be complementary to the well-known pattern of ‘Isolation by Distance’ (IBD), in which the divergence of closely related populations (via any evolutionary process) is associated with geographic isolation. The barn swallow Hirundo rustica complex comprises six closely related subspecies, where divergent sexual selection is associated with phenotypic differentiation among allopatric populations. To investigate the relative contributions of selection and geographic distance to genome-wide differentiation, we compared genotypic and phenotypic variation from 350 barn swallows sampled across eight populations (28 pairwise comparisons) from four different subspecies. We report a draft whole genome sequence for H. rustica, to which we aligned a set of 9,493 single nucleotide polymorphisms (SNPs). Using statistical approaches to control for spatial autocorrelation of phenotypic variables and geographic distance, we find that divergence in traits related to migratory behavior and sexual signaling, as well as geographic distance together, explain over 70% of genome-wide divergence among populations. Controlling for IBD, we find 42% of genome-wide divergence is attributable to IBA through pairwise differences in traits related to migratory behavior and sexual signaling alone. By (i) combining these results with prior studies of how selection shapes morphological differentiation and (ii) accounting for spatial autocorrelation, we infer that morphological adaptation plays a large role in shaping population-level differentiation in this group of closely related populations.

地理隔离下的种群分化由多种因素共同驱动。自然选择与性选择可能在塑造种群分化模式中发挥关键作用，该模式被称为‘适应驱动隔离（Isolation by Adaptation, IBA）’。适应驱动隔离（IBA）可与广为人知的‘距离驱动隔离（Isolation by Distance, IBD）’模式互为补充：后者指亲缘关系较近的种群经任意演化过程产生的分化，与地理隔离程度呈正相关。家燕（Hirundo rustica）复合群包含6个亲缘关系紧密的亚种，其异域种群间的表型分化与性选择分化密切相关。为探究选择与地理距离对全基因组分化的相对贡献，本研究对来自4个亚种、8个种群（共28组两两比对）的350只家燕的基因型与表型变异进行了比较分析。本研究构建了家燕的全基因组草图序列，并以此为参照比对得到9493个单核苷酸多态性（Single Nucleotide Polymorphisms, SNPs）位点。本研究采用控制表型变量与地理距离空间自相关的统计方法，发现与迁徙行为、性信号相关的性状分化结合地理距离，共同解释了种群间70%以上的全基因组分化。在控制距离驱动隔离（IBD）的前提下，仅通过迁徙行为与性信号相关性状的两两差异，即可归因于适应驱动隔离（IBA）的全基因组分化占比达42%。本研究（1）将上述结果与此前关于选择如何塑造形态分化的研究相结合，（2）同时考虑空间自相关效应，由此推断：在该亲缘关系紧密的种群类群中，形态适应对种群水平的分化具有显著塑造作用。