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

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 (DipteraChironomidae) 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. Chironomidae

Karyotype and COI gene sequence of Chironomusheteropilicornis Wülker, 1996 (Diptera, Chironomidae) from the Gydan Peninsula, Russia

The karyotype features and gene COI sequence of Chironomusheteropilicornis Wülker, 1996 from the Gydan Peninsula are presented for the first time. Nine banding sequences were determined, eight of them hpiA2, hpiB1, hpiC1, hpiC2, hpiD1, hpiE1, hpiF3 and hpiG1 were previously known from European, Georgian (South Caucasus) and Siberian populations. One new banding sequence for Ch.heteropilicornis, hpiB2, was found. The hpiA2 banding sequence was found in all individuals, and this is its second finding after the Georgian population (Karmokov 2019). The hpiF3 banding sequence was found only in the homozygous state. Additional B-chromosomes are absent. The genetic distances (K2P) between Ch.heteropilicornis COI gene sequence from Gydan Peninsula and Norway are 1.1--1.3%, and Georgia - 1.8%, much lower than the commonly accepted threshold of 3% for species of genus Chironomus Meigen, 1803. The phylogenetic tree for COI gene sequences estimated by Bayesian inference showed geographically determined clusters of Norway and Gydan and a separate lineage of the Georgian population of Ch.heteropilicornis. The analysis of karyotype and COI gene sequences shows that the population of Ch.heteropilicornis from the Gydan Peninsula has an intermediate position within the Ch.pilicornis group between Georgian, Yakutian and Norwegian populations. The position of Ch.pilicornis Fabricius, 1787 from Canada and Greenland on the phylogenetic tree is discussed.

The revision of chromosome III (EF) mapping in Chironomus plumosus (Linnaeus, 1758) group (Diptera, Chironomidae)

A revision of mapping of main and alternative banding sequences in chromosome III (EF) has been made for 14 species of the Chironomus plumosus group. In total, new versions of mapping are presented for 18 banding sequences of arm E and 18 banding sequences of arm F. A new way of tracing the origins of banding sequences in chromosome III of the Ch. plumosus group in comparison with basic banding sequences of the genus Chironomus is suggested. The presented data indicate that h'pluE2 in arm E and p'borF2 in arm F are the closest to banding sequences of Ch. piger Strenzke, 1959 and thus should be considered the most ancient among banding sequences of chromosome III in the Ch. plumosus group. Phylogenetic relationships of banding sequences of chromosome III are discussed.

A revision of chromosome II (CD) mapping in Chironomus plumosus (Linnaeus, 1758) group (Diptera, Chironomidae)

A revision of the main and alternative banding sequences in chromosome II (CD) has been made for all 14 species of the Chironomus plumosus (Linnaeus, 1758)group. A new version of mapping has been suggested for 10 out of 18 banding sequences of arm C and 12 out of 22 banding sequences of arm D. Mapping of 7 banding sequences has been done for the first time according to the Keyl-Devai system. Phylogenetic relationships of banding sequences of chromosome II have been discussed.

Utility of DNA taxonomy and barcoding for the inference of larval community structure in morphologically cryptic Chironomus (Diptera) species

Biodiversity studies require species level analyses for the accurate assessment of community structures. However, while specialized taxonomic knowledge is only rarely available for routine identifications, DNA taxonomy and DNA barcoding could provide the taxonomic basis for ecological inferences. In this study, we assessed the community structure of sediment dwelling, morphologically cryptic Chironomus larvae in the Rhine-valley plain/Germany, comparing larval type classification, cytotaxonomy, DNA taxonomy and barcoding. While larval type classification performed poorly, cytotaxonomy and DNA-based methods yielded comparable results: detrended correspondence analysis and permutation analyses indicated that the assemblages are not randomly but competitively structured. However, DNA taxonomy identified an additional species that could not be resolved by the traditional method. We argue that DNA-based identification methods such as DNA barcoding can be a valuable tool to increase accuracy, objectivity and comparability of the taxonomic assessment in biodiversity and community ecology studies.

Inherited and somatic cytogenetic variability in Palearctic populations of Chironomus riparius Meigen 1804 (Diptera, Chironomidae)

Inter- and intracytogenetic variability was analyzed in 13 natural Palearctic populations of Chironomus riparius Meigen 1804 (syn. Chironomus thummi) by examining hereditary and somatic aberrations (mainly inversions) of the salivary gland polytene chromosomes. In total, 77 different types of inherited inversion sequences and 184 different types of somatic inversions were found. The median percent frequency of inherited inversions was 1.4% and karyotypic divergence between populations was very low. Most hereditary inversions were endemic and always in a heterozygous state. Only six inversion sequences, each of them shared by two very distant populations, may be considered a relic of very ancient ancestral inversions. Unlike inherited inversions, occurrence of somatic aberrations seems to increase with the overall rise in the level of heavy metal pollution of the sediments from which larvae were sampled. In contrast with what occurs in populations of other chironomid species, populations of C. riparius do not seem to undergo a process of cytogenetic differentiation.

Inversion polymorphism in a Connecticut RiverAxarusspecies (Diptera: Chironomidae): biometric effects of a triple inversion heterozygote

The authors sampled three spatially isolated populations of a chironomid midge in the genus Axarus living in the Connecticut River both early and late in the larval life cycle of one generation. Larvae were scored for both length and inversion frequency using the polytene chromosomes from salivary gland cells. We found polymorphism for four paracentric inversions. Inversion C1–6exhibits a geographic cline, increasing in frequency with increasing latitude but remaining stable over time. Also stable over time were two other paracentric inversions designated A1–5and F13–20, which were present at similar frequencies in all populations. None of these inversions was associated with larval length. A complex triple inversion designated G2–7was significantly correlated with decreased larval length and also exhibited a significant increase in frequency (within one cohort) in the two more northerly populations. We propose that this increase is due to size-selective predation eliminating larger larvae.

Phylogeny of the genus Chironomus (Diptera) inferred from DNA sequences of mitochondrial cytochrome b and cytochrome oxidase I

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.

Intercontinental karyotypic differentiation of Chironomus entis Shobanov, a Holarctic member of the C. plumosus group (Diptera, Chironomidae)

Analysis of banding sequences of polytene chromosomes in Palearctic (Russian) and Nearctic (North American) Chironomus entis shows strong karyotype divergence between populations on the two continents. Four out of seven chromosomal arms in the North American C. entis karyotype are characterized by sequences found only in the Nearctic. In total, 44 banding sequences are now known for this species across the Holarctic, including 22 exclusively Palearctic, 6 Holarctic, and 16 exclusively Nearctic sequences. The degree of cytogenetic differentiation between Palearctic and Nearctic C. entis populations is an order of magnitude greater than differentiation among populations within either continent, but is only one third as great as the cytogenetic distance between the sibling species C. entis and C. plumosus. C. entis is the only sibling species of C. plumosus uncovered during cytological identification of Chironomus species from more than 50 North American lakes, indicating that the plumosus sibling-species group is much smaller in the Nearctic than in the Palearctic, where a dozen sibling species are known. Cytogenetic distance values calculated between Nearctic and Palearctic representatives of both C. entis and its sibling species C. plumosus are similar, but result from different patterns of karyotype divergence. New World C. entis is distinguished from Old World populations by the 16 uniquely Nearctic sequences, four of which occur in the homozygous state. In contrast, North American C. plumosus has fewer uniquely Nearctic sequences, and only one that occurs as a homozygote. However, four chromosomal arms in C. plumosus that are polymorphic in the Palearctic show fixation, or near fixation, of Holarctic sequences in the Nearctic C. plumosus karyotype. Thus, both the fixation of Holarctic sequences, and the occurrence or fixation of distinctly Nearctic sequences, contribute significantly to karyotype divergence. Patterns of karyotype divergence in Palearctic and Nearctic populations of different Holarctic chironomid species are discussed relative to intercontinental cytogenetic differentiation in other dipterans.