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）可通过两种不同机制形成：地理分异（vicariance）或扩散定殖（colonization through dispersal）。区分这类异域成种机制是生物地理学研究的重大挑战之一。本研究旨在探讨一种特有岛蜥的异域隔离究竟源于地理分异还是扩散定殖。研究对象为栖息于希腊群岛主岛及周边小岛的表型多样的特有物种——斯基罗斯壁蜥（Podarcis gaigeae），我们估算了该物种孤立小岛种群与亚种在分化过程中的基因流规模与方向。我们采用隔离与迁移模型（isolation-with-migration models），对小岛-主陆种群对的种群分化时间、种群大小及种群间基因流进行了估算。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，该相关性强烈支持地理分异情景：小岛种群依次与主岛产生隔离。我们未发现斯基罗斯壁蜥指名亚种（P. g. gaigeae）内部存在显著基因流的证据。不过，主陆向小岛种群的基因流估计值随小岛面积增大呈正相关，随小岛与主陆间距离增加呈负相关。此外，我们发现基因流从亚种P. g. weigandi流向亚种P. g. gaigeae的证据，但未发现反向基因流。亚种间仍存在的基因流表明，即便在海洋构成极强扩散障碍的地理异域情景中，伴随一定基因流的分化过程仍具备可行性。