Data from: Panmixia supports divergence with gene flow in Darwin’s small ground finch, Geospiza fuliginosa, on Santa Cruz, Galápagos Islands

The divergence-with-gene-flow model of speciation has a strong theoretical basis with a growing number of plausible examples in nature, but remains hotly debated. Darwin’s finches of the Galápagos Archipelago have played an important role in our understanding of speciation processes. Recent studies suggest that this group may also provide insights into speciation via divergence with gene flow. On the island of Santa Cruz, recent studies found evidence for adaptive divergence in Darwin’s small ground finch, Geospiza fuliginosa, between ecologically contrasting arid and humid zones. Despite the short geographical distance between these zones, strong disruptive selection during low rainfall periods is expected to generate and maintain adaptive divergence. Conversely, during high rainfall periods, when disruptive selection is predicted to be weakened, population divergence in adaptive traits is expected to break down. Because periods of low and high rainfall irregularly alternate, the geographical pattern of adaptive divergence can be assumed to break down and, importantly, regenerate in situ. Here, we use microsatellite allele frequency data to assess the genetic population structure of G. fuliginosa on Santa Cruz. We sample 21 sites and four ecological zones across the island. We reject hypotheses of population substructure linked to ecological and geographical differences among sites in favour of a single panmictic population. Panmixia implies high levels of gene flow within Santa Cruz, which favours selection over genetic drift as a valid process generating phenotypic divergence in G. fuliginosa on Santa Cruz. We discuss how our findings may support classic adaptation, phenotypic plasticity, matching habitat choice or any combination of these three processes.物种形成的基因流伴随分化模型（divergence-with-gene-flow model of speciation）拥有坚实的理论基础，且自然界中涌现出越来越多符合该模型的可信案例，但该模型至今仍存在激烈争议。加拉帕戈斯群岛的达尔文雀（Darwin’s finches of the Galápagos Archipelago）在学界理解物种形成过程的历程中发挥了核心作用。近期研究表明，该类群或许也能为探究存在基因流的物种分化提供新的研究视角。在圣克鲁斯岛（Santa Cruz）上，已有研究在达尔文小地雀（Geospiza fuliginosa）中发现了适应性分化的证据：该分化存在于生态特征迥异的干旱与湿润生境带之间。尽管两类生境带的地理间距极短，但在低降雨时期，强烈的分裂选择（disruptive selection）被认为能够催生并维持这种适应性分化。反之，在高降雨时期，分裂选择的作用会被削弱，此时适应性性状的种群分化也将趋于瓦解。由于低降雨与高降雨周期无规律交替，适应性分化的地理分布模式既可发生瓦解，更重要的是，还能在原地重新形成。本研究利用微卫星等位基因频率数据（microsatellite allele frequency data），对圣克鲁斯岛上的尖嘴地雀（Geospiza fuliginosa）的种群遗传结构展开评估。我们在全岛范围内布设了21个采样位点，覆盖4个生态带。我们拒绝了“种群亚结构与各采样位点的生态、地理差异相关”这一假说，转而支持圣克鲁斯岛上的尖嘴地雀属于单一泛交种群（panmictic population）的结论。泛交（Panmixia）意味着圣克鲁斯岛内部存在高水平的基因流，这表明相较于遗传漂变（genetic drift），选择作用更可能是驱动该岛尖嘴地雀产生表型分化的有效过程。我们还探讨了本研究结果如何能够支持经典适应性、表型可塑性（phenotypic plasticity）以及生境匹配选择（matching habitat choice），或是这三种过程的任意组合。