When mtDNA COI is misleading: congruent signal of ITS2 molecular marker and morphology for North European Melanostoma Schiner, 1860 (Diptera, Syrphidae)

The northern European taxa of genus Melanostoma Schiner, 1860 (Syrphidae, Diptera) are revised. A long-standing question concerning the number of Melanostoma taxa occurring in northern Europe prompted us to contrast and compare their morphological and molecular variability. Particular uncertainty concerned the putative existence of a sibling species of Melanostoma mellinum, and the identity of the taxon Melanostoma dubium in northern Europe due to existence of morphologically similar dark forms of M. mellinum in the northern parts of its distributional range. Partial sequences of two DNA markers, the mitochondrial protein-coding gene cytochrome c oxidase subunit I (COI-3') and the nuclear second internal transcribed spacer (ITS2) were analysed separately under parsimony. The obtained COI-3' gene fragment showed taxon-specific haplotypes and haplotypes that were shared among the taxa. The ITS2 sequences presented genotypes unique to each species, and congruence with our independently established taxonomic entities. Based on congruent signal of the ITS2 sequences and study of morphological characters we establish the presence of four taxa in northern Europe: Melanostoma mellium (= M. dubium nec auctt., syn. n.), M. certum sp. n. (= M. dubium auctt.), M. mellarium stat. n. (= M. mellinum auctt. partim) and M. scalare. Lectotype designations were made for Musca mellina, Syrphus mellarius and Melanostoma mellinum var. melanatus. The following synonymies were established: Melanostoma mellarium = Melanostoma melanatum syn. n.; Melanostoma mellinum = Scaeva dubia syn. n., Melanostoma tschernovi syn. n., and Melanostoma clausseni syn. n. Morphological circumscriptions of the taxa and an identification key are presented.