Phylogeny of the Genus Chironomus (Diptera) Inferred from DNA Sequences of Mitochondrial Cytochrome b and Cytochrome oxidase I

Abstract

Two mitochondrial genes, Cytochrome b (Cytb) and Cytochrome c oxidase subunit I (COI), have been used as phylogenetic markers in Chironomids. The nucleotide sequences of 685 bp from Cytb and 596 bp from COI have been determined for 36 Chironomus species from the Palearctic, or Holarctic, and Australasia. The concatenated sequence of 1281 bp from both genes was used to investigate the phylogenetic relationships among these species. The nucleotide sequence alignments were used for construction of phylogenetic trees based on maximum-parsimony and neighbor-joining methods. Both techniques produced similar phylogenies. Monophyly of the genus Chironomus is supported by a bootstrap value of 100% at the basal branch. Six clusters of species have been revealed with high bootstrap values supporting both monophyly of each cluster and the validity of the branching order within each cluster. Four species, C. circumdatus, C. nepeanensis, C. dorsalis, and C. crassiforceps, cannot be placed into any cluster. Cytological phylogenies were constructed using the same set of species, except for C. biwaprimus. These trees showed many similarities to that obtained from the mitochondrial (mt) sequence analysis, but also a number of significant differences. When compared with the tree constructed from the sequence of 23 species available for one of the globin genes, globin 2b (gb2b), there was better support for the mt tree than for the cytological trees. An intron, which varies in its occurrence and position in gb2b, was also investigated and the distribution of the introns supports the phylogenetic history of the genus Chironomus obtained with mt data. The differences observed in the cytological trees seem to be attributable more to the retention of the same chromosome banding sequence across several species, rather than convergent evolutionary events. An important question is the determination of the position of the subgenus Camptochironomus in relation to the representatives of the nominal subgenus Chironomus, since it has been suggested that this is a separate genus. The Camptochironomus species are internal to the trees and have arisen more recently than some of the species of the subgenus Chironomus, indicating that they are not sufficiently differentiated to be considered more than a subgenus.