Abstract
Molecular phylogenies of extant species are considered effective tools to infer mechanisms of speciation. Here, we benefit from this utility to investigate the evolutionary history of an organismal group linked to different aquatic ecosystems, the microgastropod genus Pseudamnicola (family Hydrobiidae). Previous studies have found around 45 species of the nominal subgenus P. (Pseudamnicola), most of them in coastal stream localities of several Mediterranean islands and mainland territories, whereas only 12 species of the other subgenus, P. (Corrosella), have been collected from springs and headwaters of mountainous regions of the Iberian Peninsula and south of France. As springs often act as isolated habitats affecting dispersion and constraining gene flow, we supposed that the temporal history and mode of diversification of species from both subgenera should differ and therefore be reflected in their phylogenetic patterns. To assess this hypothesis, we performed a molecular phylogeny based on mitochondrial and nuclear DNA sequences and later conducted an independent analysis to examine the potential effect of certain geographic and ecological variables in the genetic divergences of the subgenera. Additionally, we estimated the ancestral area of diversification of both groups. Published anatomical revisions and our molecular analyses suggest that the genus Pseudamnicola should be divided into three genera: the two previous subgenera plus a new one described here. As postulated, the evolution of the spring organisms was strongly related to habitat fragmentation and isolation, whereas dispersal followed by divergence seem to have been the most common speciation processes for euryhaline species inhabiting coastal streams and low river stages in which waters remain connected. On the contrary, rather than habitat fragmentation or dispersion, environmental conditions have played a larger role during the deep divergent split leading to the three genera.
Highlights
The current species diversity is a result of the interaction of several evolutionary and ecological processes which generate and define each species
Since springs often act as isolated habitats affecting dispersion and constraining gene flow, we supposed that the temporal history and mode of diversification of species from both subgenera should differ and be reflected in their phylogenetic patterns
The evolution of the spring organisms was strongly related to habitat fragmentation and isolation, whereas dispersal followed by divergence seem to have been the most common speciation processes for euryhaline species inhabiting coastal streams and low river stages in which waters remain connected
Summary
The current species diversity is a result of the interaction of several evolutionary and ecological processes which generate and define each species. Lineages divergence in allopatry is considered the most frequent scenario for speciation (Endler 1977; Coyne & Orr 2004), modulated by population dispersion and the presence of geographical barriers that maintain isolated the split populations Freshwater gastropods, which are typically habitat specialist, gather those properties of limited dispersal capabilities and narrow‐ranged distributions, and tend to be strongly affected by variation in their habitat. For this reason they represent an ideal model to investigate speciation processes associated with isolating mechanisms (e.g., Mavárez et al 2002; Albrecht et al 2007; Rintelen et al.2012; Schreiber et al 2012; Delicado et al 2013). One potential candidate taxon that may provide valuable information about evolutionary processes in different environments is the microgastropod family Hydrobiidae Stimpson, 1965
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