Increased geographic sampling suggests incomplete lineage sorting and recent introgression between Pyrrhosoma nymphula (Sulzer, 1776) and P. elisabethae Schmidt, 1948 in the Western Palearctic

We analysed COI and ITS sequences from a total of 69 European Pyrrhosoma nymphula (Sulzer, 1776) and three P. elisabethae Schmidt, 1948 to explore species boundaries and phylogeographic patterns in their Western Palearctic distributions. We found that phylogenetic and haplotype network analyses support previous results that the widespread P. nymphula and the endangered P. elisabethae are distinct species, and that P. nymphula in North Africa are distinct from P. nymphula in Europe. However, our results also suggest that neither diversification is complete as we found evidence for introgression of mitochondrial DNA between P. elisabethae and eastern Europe P. nymphula, as well as possible incomplete lineage sorting. Finally, our results indicate that while P. nymphu­la likely recolonized most of Europe from an Iberian Peninsula refugium following the Weichsel Glaciation, separate refugia possibly existed in North Africa, southern Italy, and for P. elisabethae in the southwestern Balkan.