Sky island diversification in the Merodon rufus group (Diptera, Syrphidae)-recent vicariance in south-east Europe

Climatic changes associated with Pleistocene glacial cycles had profound effects on the genetic diversification and distribution of many taxa, especially from environmentally sensitive habitats such as mountain regions. The DNA sequence data (mtCOI and 28S RNA genes) derived from the Merodon rufus group (Diptera: Syrphidae) in central, eastern, and southern Europe was analyzed. Environmental niche modeling (ENM) and coalescent simulations also were performed to describe diversification events previously recognized via morphological analysis and to elucidate its evolutionary mechanism. Results revealed that M. rufus group is composed of four well-supported lineages, three of which belong to new species from Mediterranean mountains, namely M. kozufensis sp. nova, M. olympius sp. nova, and M. orjensis sp. nova. According to the divergence time estimates, lineage diversification most probably occurred during the Pleistocene by the colonization model rather than the fragmentation of a widely distributed common ancestor's range. ENM results showed potential overlap of climatic refugia on the Balkan Peninsula of the M. rufus group and the beech forests, suggesting a possible association with this habitat type. Merodon rufus Meigen, 1838 probably colonized further from these refugia and spread across other parts of Europe during the Holocene.