Karyotype structure and polymorphism peculiarities of Chironomus nuditarsis Keyl, 1961 (Diptera, Chironomidae) from natural populations of North Caucasus

The study presents data on the karyotype characteristics and features of chromosomal polymorphism of Chironomus nuditarsis Keyl, 1961 (Diptera, Chironomidae) from seven natural populations of Caucasus (Northwest, Central and East Caucasus). We found 16 banding sequences in the Caucasian populations. We observed inversion polymorphism almost in all chromosome arms except for arms C and E. The genetic distances between all the studied populations of Ch. nuditarsis were calculated using Nei criteria (1972). In spite of relative geographic proximity, the genetic distances between populations of the Caucasus are quite big, and they do not form a single cluster of Caucasian populations. The population of the Northwest Caucasus goes to European cluster; the populations of Central and East Caucasus form their own separate clusters. The principal component analysis (PCA) shows the similar picture. We suggest that such a clear separation of Caucasian populations in distinct clusters is a result of differences of collection sites in terms of geography and climate (complex diverse terrain and microclimate conditions). Four of the Caucasian populations do not follow Hardy-Weinberg expectation. In two populations, there being a marked deficiency of heterozygotes in arms B, F and G. In two other populations, there being a marked excess of heterozygotes in arms B and G. One can suggest that observed pictures could be a reflection of multi-directional selection of heterozygotes in different populations. The populations of Ch. nuditarsis from different parts of the Caucasus possibly diverged from each other at the level of subspecies. All the obtained data are indicative of the complex genetic structure of Caucasian populations of Ch. nuditarsis and total complexity of microevolution processes occurring in the Caucasus region.