Data from: Vicariance divergence and gene flow among islet populations of an endemic lizard

Allopatry and allopatric speciation can arise through two different mechanisms: vicariance or colonization through dispersal. Distinguishing between these different allopatric mechanisms is difficult and one of the major challenges in biogeographical research. Here, we address whether allopatric isolation in an endemic island lizard is the result of vicariance or dispersal. We estimated the amount and direction of gene flow during the divergence of isolated islet populations and subspecies of the endemic Skyros wall lizard Podarcis gaigeae, a phenotypically variable species which inhabits a major island and small islets in the Greek archipelago. We applied isolation-with-migration models to estimate population divergence times, population sizes and gene flow between islet–mainland population pairs. Divergence times were significantly correlated with independently estimated geological divergence times. This correlation strongly supports a vicariance scenario where islet populations have sequentially become isolated from the major island. We did not find evidence for significant gene flow within P. g. gaigeae. However, gene flow estimates from the mainland to the islet populations was positively affected by islet area and negatively by distance between the islet and mainland. We also found evidence for gene flow from one subspecies (P. g. weigandi) into another (P. g. gaigeae), but not in the other direction. Ongoing gene flow between the subspecies suggests that even in this geographically allopatric scenario with the sea posing a strong barrier to dispersal, divergence with some gene flow is still feasible.异域分布（allopatry）与异域成种（allopatric speciation）可通过两种截然不同的机制形成：分隔分化（vicariance）或通过扩散实现的定殖（colonization through dispersal）。区分这些不同的异域分布机制难度颇高，亦是生物地理学研究的核心挑战之一。本研究旨在探究一种特有岛蜥的异域隔离究竟源自分隔分化还是扩散定殖。我们针对栖息于希腊群岛主岛及周边小型小岛、表型多样的特有物种——斯基罗斯壁蜥（Podarcis gaigeae）的小岛种群与亚种，估算了其分化过程中的基因流规模与方向。我们应用隔离与迁移（isolation-with-migration）模型，对小岛-主岛种群对之间的种群分化时间、种群大小及基因流水平进行了估算。研究结果显示，种群分化时间与独立估算得到的地质分化时间显著相关，这一相关性强烈支持分隔分化情景：即小岛种群依次与主岛产生地理隔离。我们未发现P. g. gaigeae种内存在显著基因流的证据。不过，从主岛流向小岛种群的基因流水平会随小岛面积增大呈正向变化，随小岛与主岛间距离增加呈负向变化。我们还观测到基因流从一个亚种（P. g. weigandi）流向另一亚种（P. g. gaigeae）的证据，但未发现反向的基因流事件。亚种间仍存在持续的基因流，这表明即便在海洋构成强烈扩散屏障的地理异域情景中，伴随一定基因流的物种分化过程依然具备可行性。