Bayesian phylogeographic inferences reveal contrasting colonization dynamics among European groundwater isopods

Abstract

The potentially important role of northern microrefugia during postglacial dispersal is challenging the view of southern Europe as a refuge and source area of European biota. In groundwaters, large geographic ranges of presumably good dispersers are increasingly suspected to consist of assemblages of cryptic species with narrow ranges. Moreover, a large species range, even when confirmed by molecular evidence, tells us little about the spatiotemporal dynamics of dispersal. Here, we used phylogenetic inferences, species delineation methods and Bayesian phylogeographic diffusion models to test for the likelihood of postglacial colonization from distant refugia among five morphospecies of Proasellus (Isopoda, Asellidae). All morphospecies except one were monophyletic, but they comprised a total of 15-17 cryptic species. Three cryptic species retained ranges that spanned a distance >650 km, similar to that of the nominal morphospecies. Bayesian diffusion models based on mitochondrial markers revealed considerable spatiotemporal heterogeneity in dispersal rates, suggesting that short-time dispersal windows were instrumental in shaping species ranges. Only one species was found to experience a recent, presumably postglacial, range expansion. The Jura and Alpine foothills probably played a major role in maintaining diversity within Proasellus in northern regions by acting both as diversification hotspots and Pleistocene refugia. Gaining insight into the spatiotemporal heterogeneity of dispersal rates revealed contrasting colonization dynamics among species that were not consistent with a global postglacial colonization of Europe from distant refugia.

Do cryptic species matter in macroecology? Sequencing European groundwater crustaceans yields smaller ranges but does not challenge biodiversity determinants

“…For instance, species delimitation methods that are based on allele sharing (Flot et al ) or on multilocus coalescence (Yang and Rannala ) could change the number of SHs in our dataset by splitting divergent entities that have not yet reached reciprocal monophyly or by lumping entities that are still connected by gene flow (Knowles and Carstens , Leaché et al ). Yet, the three MMs used in the present study provided similar richness estimates, as in previous groundwater studies showing that the variation in the number of SHs among different MMs is typically smaller than between them and morphology‐based taxonomy (Eme et al , Morvan et al ). This matches the result of a recent simulation study showing that single‐locus tree‐based, distance‐based and allele sharing‐based approaches give congruent species hypotheses when dealing with highly variable markers in species of small effective population size and low speciation rate (Dellicour and Flot ).…”

Trophic ecology of groundwater species reveals specialization in a low‐productivity environment

“…Phylogenetic studies confirmed that populations of P. valdensis and P. cavaticus belonged to two distinct monophyletic taxa, the five P. valdensis populations belonging to the same species, while populations of P. cavaticus represented a complex of sibling species (Eme et al . , ; Morvan et al . ).…”

Geomorphic influence on intraspecific genetic differentiation and diversity along hyporheic corridors

“…Using Bayesian phylogeographic inferences, Eme et al. () showed that three species of interstitial groundwater asellids (Pancrustacea, Isopoda) experienced considerable historical range expansion in Northern Europe. However, dispersal occurred in short bursts, indicating that hyporheic corridors facilitated the movement of animals during short‐time environmental windows of increased functional connectivity.…”

“…Eme et al. () suggested that these windows might correspond to periods of intense post‐glacial sediment deposition, thereby implicitly linking dispersal dynamics to climate‐mediated changes in the balance between the transport and supply of sediment. Yet, it remains to be tested whether dispersal is indeed facilitated by increasing sediment deposition.…”