Evolution of postgonites in frit flies (Diptera, Chloropidae, Meromyza)

Evolutionary trends of the morphometric characteristics of postgonites (structures important for copulation) and variability of the mtDNA COI gene region were analyzed for 27 species of the genus Meromyza Mg. The total area, the area and height of the protuberance, and the length ratio of the main part and the protuberance were analyzed for the anterior process of the postgonite. The height and way of attachment were analyzed for the posterior process of the postgonite. Based on the mtDNA COI locus, eight clusters were distinguished in Network; they formed three groups differing in the area of the anterior process and the way of attachment of the posterior process. The size characteristics of the male sexual appendages of the ancestral forms within the genus Meromyza show an evolutionary trend toward an increase in the postgonite area, while within the clusters there is a trend toward a decrease in this area relative to the species most resembling the hypothetical ancestor. The ancestral forms were characterized by a small area of the postgonite and a short and narrow protuberance of its anterior process. An increase in this area may have led to reduction of the statistical significance of differences in the protuberance and to the appearance of a flap on the lateral part of the postgonite. The functional significance of the postgonite elements and the flap is discussed. Based on the studied morphometric characteristics, the species M. maculata and M. cognata can be placed in the known clusters, even though their COI sequences have not been determined.