Radiating on Oceanic Islands: Patterns and Processes of Speciation in the Land Snail Genus Theba (Risso 1826)

Zoologisches Forschungsmuseum Alexander Koenig, Bonn, Germany.
PLoS ONE (Impact Factor: 3.23). 09/2012; 7(4):e34339. DOI: 10.1371/journal.pone.0034339
Source: PubMed


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.

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Available from: Rainer Hutterer, Oct 03, 2015
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    • "In this study, the effect of environmental heterogeneity per se was consistent across spider mobility groups, which agrees with empirical studies that show the robustness of this pattern across scales, taxa and ecological systems (Triantis et al., 2003; Borges & Hortal, 2009; Marini et al., 2010). Environmental heterogeneity provides the opportunity for speciation and, consequently, an increase in the number of species (Greve et al., 2012; Steinbauer et al., 2012). Additionally , higher environmental heterogeneity might provide the necessary habitat conditions even for specialized species (Ricklefs & Lovette, 1999). "
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