A tale of two Skimmers: complex relationships between DNA bar- codes, distributions and taxonomy in European Orthetrum cancellatum and O. coerulescens

We explore the genetic diversity and phylogeography of the dragonflies Orthetrum cancel-latum and O. coerulescens in Europe based on mitochondrial and nuclear DNA. Orthetrum cancella-tum has a clear division between a group comprising Maltese, Italian, and central and northern Euro-pean populations, and a group comprising mainly populations from southwestern and southeastern Europe, as well as some northern European specimens. We propose that the two groups represent two different Glacial refugia, one in the Italian Peninsula and one in the Balkans where the species survived during the Weichsel Glaciation. Orthetrum coerulescens shows a more complex pattern, although it too can be divided into two groups. One group comprise all the specimens we have identified as O. coe-rulescens anceps from their phenotype as well as specimens from Spain, Montenegro, and Pakistan, and some specimens from Italiy, Poland and Bulgaria. The other group comprise all other specimens from central and northern Europe, almost all specimens from Italy and Bulgaria, and all specimens from Malta. We propose that the latter group represents an Italian Glacial refugium from which the species spread to both central Europe, Malta and southern Balkan (Bulgaria) after the end of the Weich-sel Glaciation. As specimens from Spain and Bulgaria, which were identified as O. coerulescens coe-rulescens group with specimens identified as O. coerulescens anceps we conclude that the two subspe-cies mix more or less freely across the Mediterranean and question the validity of two subspecies.

Automated summary

Based on mitochondrial and nuclear DNA, the study explored the genetic diversity and phylogeography of dragonfly populations in Europe, revealing different glacial refugia and potential dispersal routes for the species. The presence of distinct subspecies and their intermixing across regions raises questions about the validity of subspecies classification in the studied dragonfly populations.