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：地理分异（vicariance）或通过扩散实现的定殖（colonization through dispersal）。区分这类不同的异域成种机制颇具挑战性，亦是生物地理学研究的核心难题之一。本研究旨在探究一种特有岛栖蜥蜴的异域隔离究竟源自地理分异还是扩散定殖。我们以栖息于希腊群岛主岛及周边小型岩礁岛的表型多样物种——斯基罗斯壁蜥蜴（Podarcis gaigeae）的孤立岩礁岛种群与亚种（subspecies）为研究对象，估算了其分化过程中的基因流（gene flow）规模与方向。我们采用隔离迁移模型（isolation-with-migration models），对岩礁岛-主岛种群对之间的种群分化时间、种群规模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呈显著相关，这一相关性强有力地支持了地理分异情景：岩礁岛种群依次与主岛产生隔离。我们未发现P. g. gaigeae亚种内存在显著基因流的证据。然而，从主岛向岩礁岛种群的基因流估算值会随岩礁岛面积增大而升高，随岩礁岛与主岛间距离增加而降低。我们还发现存在基因流从P. g. weigandi亚种流向P. g. gaigeae亚种的证据，但反向则未观察到此类基因交流。亚种间持续存在的基因流表明，即便在海洋构成强扩散障碍的地理异域情景中，伴随一定基因流的种群分化依然具备可行性。