Zoologisches Forschungsmuseum Alexander Koenig, Bonn, Germany.
PLoS One. 2012;7(4):e34339. doi: 10.1371/journal.pone.0034339. Epub 2012 Apr 6.
Island radiations have played a major role in shaping our current understanding of allopatric, sympatric and parapatric speciation. However, the fact that species divergence correlates with island size emphasizes the importance of geographic isolation (allopatry) in speciation. Based on molecular and morphological data, we investigated the diversification of the land snail genus Theba on the two Canary Islands of Lanzarote and Fuerteventura. Due to the geological history of both islands, this study system provides ideal conditions to investigate the interplay of biogeography, dispersal ability and differentiation in generating species diversity. Our analyses demonstrated extensive cryptic diversification of Theba on these islands, probably driven mainly by non-adaptive allopatric differentiation and secondary gene flow. In a few cases, we observed a complete absence of gene flow among sympatrically distributed forms suggesting an advanced stage of speciation. On the Jandía peninsula genome scans suggested genotype-environment associations and potentially adaptive diversification of two closely related Theba species to different ecological environments. We found support for the idea that genetic differentiation was enhanced by divergent selection in different environments. The diversification of Theba on both islands is therefore best explained by a mixture of non-adaptive and adaptive speciation, promoted by ecological and geomorphological factors.
岛屿辐射在塑造我们目前对异域、同域和邻域物种形成的理解方面发挥了重要作用。然而，物种分化与岛屿大小相关这一事实强调了地理隔离（异域）在物种形成中的重要性。基于分子和形态学数据，我们调查了兰萨罗特岛和富埃特文图拉岛这两个加那利群岛上的陆地蜗牛属 Theba 的多样化情况。由于两个岛屿的地质历史，这个研究系统为调查生物地理学、扩散能力和分化在产生物种多样性方面的相互作用提供了理想的条件。我们的分析表明，Theba 在这些岛屿上存在广泛的隐生多样化，可能主要是由非适应性异域分化和次级基因流驱动的。在少数情况下，我们观察到同域分布形式之间完全没有基因流，这表明已经进入了物种形成的高级阶段。在亚速尔半岛的基因组扫描中，我们发现两种密切相关的 Theba 物种对不同生态环境的基因型-环境关联和潜在适应性多样化。我们发现，遗传分化是由不同环境中的分歧选择增强的观点得到了支持。因此，Theba 在两个岛屿上的多样化最好通过非适应性和适应性物种形成的混合来解释，这是由生态和地貌因素推动的。
