Origin and in situ diversification in Hemidactylus geckos of the Socotra Archipelago

The Socotra Archipelago is an ancient continental fragment of Gondwanan origin and one of the most isolated landforms on Earth and a biodiversity hotspot. Yet the biogeography and evolutionary history of its endemic fauna still remain largely overlooked. We investigate the origin, tempo and mode of diversification in the Hemidactylus geckos of the Socotra Archipelago. Concatenated and multilocus species coalescent analyses of Hemidactylus from Arabia and North Africa indicate that the Hemidactylus from Socotra do not form a monophyletic group and branch as three independent and well-supported clades instead. Both the chronogram inferred using the gene tree approach of BEAST and the age-calibrated multilocus species tree obtained using *BEAST suggest that the origin of Hemidactylus from Socotra may have involved a first vicariance event, that occurred in the Early Miocene, followed by two independent transoceanic dispersal events that occurred more recently, during the Pliocene. Within Socotra, we analyzed patterns of genetic diversity, the phylogeography and the demographic history in all seven non-introduced species of Hemidactylus. Results based on two mitochondrial and two nuclear loci from 144 individuals revealed complex patterns of within-island diversification and high levels of intra-species genetic divergence. The interplay of both historical and ecological factors seems to have a role in the speciation process of this group of geckos. Interestingly, the case of H. forbesii and H. oxyrhinus, which inhabit the island of Abd al Kuri with an area of 133 km², may represent one of the most extreme cases of intra-island speciation in reptiles ever reported.

索科特拉群岛（Socotra Archipelago）是起源于冈瓦纳大陆的古老陆块，同时也是地球上最孤立的地貌之一与全球生物多样性热点地区。然而，该群岛特有动物群的生物地理学特征与演化历史，在很大程度上仍未得到充分研究。本研究针对索科特拉群岛的半叶趾虎属（Hemidactylus）壁虎，探究其起源、多样化速率与演化模式。对采自阿拉伯与北非的半叶趾虎开展的串联序列分析及多位点物种溯祖分析显示，索科特拉群岛的半叶趾虎并非单系群，而是形成三个独立且支持度极高的演化支。基于BEAST基因树法构建的时间校准树，以及使用*BEAST得到的年龄校准多位点物种树均表明，索科特拉群岛半叶趾虎的起源可能涉及一次发生于中新世早期的隔离分化事件，随后在更晚的上新世时期发生了两次独立的跨洋扩散事件。在索科特拉群岛内部，我们对全部7种非引入性半叶趾虎的遗传多样性模式、系统地理学特征与种群历史进行了分析。基于144个个体的2个线粒体基因座与2个核基因座的研究结果显示，岛内多样化模式复杂，且种内遗传分化程度较高。历史与生态因素的共同作用似乎在该类壁虎的物种形成过程中发挥了重要作用。值得注意的是，栖息于面积133平方千米的阿卜杜勒库里岛（Abd al Kuri）的H. forbesii与H. oxyrhinus，可能是爬行动物中已报道的最极端的岛内物种形成案例之一。