Cytogenetic divergence of genomes in Chironomus plumosus group (Diptera: Chironomidae)

The phylogenetic relationships and karyotype differentiation of 14 sibling species of Chironomus plumosus group were studied using comparative analysis of polytene chromosome banding sequences. Revision of banding sequence pools has been made for all species. Main and alternative banding sequences of 6 chromosomal arms (A, B, C, D, E, and F) of each species were used for the analysis. In total 133 banding sequences were analysed. Phylogenetic trees for each arm were constructed on the basis of break point numbers obtained from the pairwise comparison of banding sequences in the arm. Analysis of divergence of banding sequences in individual chromosomal arms has shown that different arms make an uneven contribution to differentiation of the Ch. plumosus group. Considering the level of divergence and the input of each chromosomal arm into karyotype differentiation of the Ch. plumosus group, the arms could be arranged as: E < F < A ≤ B < D (≤ G) ≤ C. To analyse the phylogenetic relationships of species of Ch. plumosus group integral phylogenetic NJ trees were constructed on the basis of combined data on separate chromosomal arms. It was shown that Chironomus sp. K, Ch. agilis, and Ch. sp. prope agilis are the most divergent species in the Ch. plumosus group. Among the other species Ch. entis, Ch. muratensis, Ch. nudiventris, and Chironomus sp. J also show high level of divergence, as they form separate subcluster. To evaluate how the number of arms used for tree construction influences its topology, 3-arm (A, E, F), 5-arm (A, C, D, E, F) and 6-arm (A, B, C, D, E, F) trees were constructed. The study shows that the combination of data on 5 out of 7 chromosomal arms (about 70% of the genome) provides rather reliable results. Key word: Chironomus, Ch. plumosus group, divergence, evolution, chromosome, karyotype, banding sequence, phylogenetic tree.