Living on the mountains: Patterns and causes of diversification in the springsnail subgenus Pseudamnicola (Corrosella) (Mollusca: Caenogastropoda: Hydrobiidae)

- We analyze modes of speciation and causes of diversification in the hydrobiid subgenus Pseudamnicola (Corrosella).
- Coalescent methods reveal three main speciation events during the upper Miocene to Pleistocene.
- Diversification mechanisms are a result of habitat fragmentation (non-adaptive radiation).
- Formation of Iberian mountain ranges and configuration of the hydrographic system played important roles in speciation.

Hydrobiidae is one of the largest families of freshwater gastropods comprised of approximately 400 genera and 1000 species. Despite this high level of diversity, most hydrobiid species inhabit fragile ecosystems in restricted distribution areas. In this work, we analyze modes of speciation and causes of diversification in the hydrobiid springsnail subgenus Pseudamnicola (Corrosella). Species of this group typically live in nutrient poor springs and streams and are restricted to mountainous regions of the Iberian Peninsula (Spain) and Southern France. Previous morphological and molecular (based only on the cytochrome c oxidase subunit I (COI) gene) studies revealed 11 nominal Corrosella species. In this study, we enhance published molecular results by generating new data from mitochondrial (16S rRNA and COI) and nuclear ribosomal regions (18S and 28S rRNA) from 50 Corrosella populations. As a result of this study we have identified one new species, making a total of twelve recognized species in the subgenus Corrosella. Our phylogenetic results also reveal the existence of three lineages within the subgenus, and the estimation of time divergence indicates the occurrence of three main speciation events during the upper Miocene to Pleistocene. We test the influence of several geographical and ecological variables and observe that diversification patterns are related to habitat fragmentation rather than environmental conditions. This result suggests that the high level of diversity observed within the subgenus may have resulted from a non-adaptive radiation. The formation of the Iberian Peninsula mountain ranges (the Pyrenees in the north and the Betic Cordillera in the south) and the configuration of the Iberian current hydrographic system played important roles in Corrosella speciation. Additionally, during the Miocene the Iberian Peninsula experienced a gradient of increasing temperature and dryness from north to south, which together with a high level of tectonic activity, may have caused the majority of the diversity found in the southern Iberian Peninsula.