Data from: Spatially explicit models of divergence and genome hitchhiking

Strong barriers to genetic exchange can exist at divergently selected loci, whereas alleles at neutral loci flow more readily between populations, thus impeding divergence and speciation in the face of gene flow. However, ‘divergence hitchhiking’ theory posits that divergent selection can generate large regions of differentiation around selected loci. ‘Genome hitchhiking’ theory suggests that selection can also cause reductions in average genome-wide rates of gene flow, resulting in widespread genomic divergence (rather than divergence only around specific selected loci). Spatial heterogeneity is ubiquitous in nature, yet previous models of genetic barriers to gene flow have explored limited combinations of spatial and selective scenarios. Using simulations of secondary contact of populations, we explore barriers to gene flow in various selective and spatial contexts in continuous, two-dimensional, spatially explicit environments. In general, effects of hitchhiking are strongest in environments with regular spatial patterning of starkly divergent habitat types. When divergent selection is very strong, the absence of intermediate habitat types increases the effects of hitchhiking. However, when selection is moderate or weak, regular (versus random) spatial arrangement of habitat types becomes more important than the presence of intermediate habitats per se. We also document counterintuitive processes arising from the stochastic interplay of selection, gene flow, and drift. Our results indicate that generalization of results from two-deme models requires caution and increase understanding of the genomic and geographic basis of population divergence.分歧选择位点（divergently selected loci）处可能存在极强的遗传交换屏障，而中性位点（neutral loci）的等位基因在种群间更易流动，因此在基因流存在的情况下会阻碍种群分化与物种形成。然而，“分化搭车（divergence hitchhiking）”理论提出，分歧选择可在选定位点周围形成大范围的分化区域。“基因组搭车（Genome hitchhiking）”理论则认为，选择还可降低全基因组范围内的平均基因流速率，进而引发广泛的基因组分化（而非仅局限于特定选定位点周围的分化）。空间异质性（spatial heterogeneity）在自然界中无处不在，但此前的基因流遗传屏障模型仅探索了有限的空间与选择情景组合。本研究通过种群二次接触（secondary contact of populations）的模拟实验，在连续二维空间显性环境（spatially explicit environments）中的多种选择与空间情景下，探究基因流屏障的形成机制。总体而言，在生境类型差异显著且空间格局规整的环境中，搭车效应最为显著。当分歧选择强度极高时，缺乏过渡生境类型会增强搭车效应。但若选择强度处于中等或较弱水平，则生境类型的规整（相较于随机）空间排布，其重要性要高于过渡生境本身的存在与否。本研究还揭示了由选择、基因流与遗传漂变（drift）的随机互作所产生的反直觉过程。研究结果表明，对双局域种群模型（two-deme models）结果的推广需谨慎，同时也加深了我们对种群分化的基因组与地理基础的理解。