The Evolution of Holarctic Grass Flies of the Genus Meromyza Mg. (Diptera, Chloropidae) in the Neogene

An analysis of the history of diversification of grass flies of the genus Meromyza in the Northern Hemisphere during the Neogene period was carried out. A chronogram based on the gene locus of mtDNA CO1 (770 bp) of 29 dominant species of Meromyza flies was constructed in the BEAST program. The formation time of the common hypothetical ancestor of Meromyza flies is 13.9 Ma. The genus Meromyza originated in Europe, with the further formation of Dauro-Mongolian and North American secondary centers of speciation. Based on molecular data and male postgonite morphology, 5 clusters were identified, and the time of their diversification and distribution was determined. Species of the “variegata” cluster, distributed throughout Europe, have postgonites of average size, Euro-Asian species have smaller postgonites, and species from the “saltatrix” and “pratorum” clusters spread in Asia, have the larger ones. Three Meromyza species are spread throughout the northern hemisphere, including North America. Grass flies reached the territory of North America via Berengia no later than 5–6 Ma. In each cluster, species of grass flies close to the ancestral haplotype are polyphagous, and develop on host plants from various subtribes. It has been shown that the decrease in average annual temperatures during the Neogene period is correlated with an increase in the species diversity of grass flies. The abrupt change in temperature during the Quaternary period led to an outbreak of speciation within 2.5 Ma–400 thousand years ago.