Karyotype characteristics and gene COI sequences of Chironomus bonus Shilova et Dzhvarsheishvili, 1974 (Diptera, Chironomidae) from the South Caucasus (Republic of Georgia, Paravani river)

Abstract

The study presents data on the karyotype characteristics and the mitochondrial gene COI sequences of the non-biting midge Chironomus bonus Shilova et sDzhvarsheishvili, 1974 (Diptera, Chironomidae) from the South Caucasus. The species belongs to the Ch. plumosus group of sibling species, one of the most widespread and successful groups in the genus Chironomus Meigen, 1803. The karyotype of the studied population is monomorphic. The morphological and chromosomal characteristics of Ch. bonus from the Caucasus are similar to those previously described for this species (Kiknadze et al. 1991a). In the phylogenetic tree based on the COI gene sequences, one can observe several clear clusters. We named them Palearctic Ch. plumosus, Far Eastern Ch. borokensis-Ch.suwai, and Nearctic Ch. entis-Ch.plumosus clusters. The calculated K2P genetic distances within each cluster have not exceeded the 3% threshold for the genus Chironomus. Contrary to this, the distances between the clusters exceed this range and correspond to separate species. The Ch. bonus sequences belong to the cluster consisting of Ch. plumosus (Linnaeus, 1758) sequences from European populations, and do not form a separate clade of the phylogenetic tree. One can suppose that the origin of the Ch. plumosus group of sibling species dates back to 5.75–3.43 million years ago (Mya), the epochs of Late Miocene (7,3–5,3 Mya) and early Pliocene (5,3–2,58 Mya). On the other hand, Palearctic Ch. plumosus, Far Eastern Ch. borokensis-Ch.suwai, and Nearctic Ch. entis-Ch. plumosus clusters appeared relatively recently in the Middle Pleistocene, 1.288–0.307 Mya. The possible relationship between the climate changes in the Pliocene and the origin of the Ch. plumosus group are discussed