Karyotype characteristics and COI gene data of Chironomus degelenus Seisebaev, Bakhtin & Siirin, 2001 (Diptera, Chironomidae) from the Eastern Caucasus (Dagestan) and its relationship with the Nearctic species Chironomus atrella (Townes, 1945)

This study provides new details on the karyotype characteristics, chromosomal polymorphism, and COI gene data of the Dipteran species Chironomus degelenus from the Eastern Caucasus. This is the first record of Ch. degelenus in the Eastern Caucasus (and Russia in General). The Caucasian population of this species shows eight banding sequences and low polymorphism. We discovered a new banding sequence, degC2, in Ch. degelenus . Only arm C showed an inversion polymorphism. There are striking similarities between the polytene chromosome banding patterns of Ch. degelenus and Ch. atrella . Therefore, we propose including Ch. degelenus in the Ch. atrella group of closely related species. Phylogenetic analysis of COI gene sequences reveals two distinct entities referred to as “ Ch. atrella ”, with a higher-than-average K2P distance of 6.2%. This pattern is attributed to “dark taxa”; genetic information in databases from unknown and taxonomically challenging species. We also discuss the potential link between the emergence of the species Ch. degelenus and Ch. atrella and Pliocene climate changes.