Karyotype characteristics and chromosomal polymorphism of Chironomus “annularius” sensu Strenzke (1959) (Diptera, Chironomidae) from the Caucasus region

Abstract

The study presents data on the karyotype characteristics and features of chromosomal polymorphism of Chironomus “annularius” sensu Strenzke (1959) (Diptera, Chironomidae) from three populations of the Caucasus region (South and Central Caucasus, and Eastern Ciscaucasia). We found 17 banding sequences in the Caucasian populations. We observed inversion polymorphism in almost all chromosome arms except for arm G. The genetic distances between all the studied populations of Ch. “annularius” were calculated using Nei criteria (1972). In spite of relative geographic proximity, the genetic distances between populations of the Caucasus are quite large, and they do not form a single cluster of Caucasian populations. The population of the South Caucasus goes to the European cluster, the population of the Central Caucasus goes to the Asian cluster and the population of Eastern Ciscaucasia does not belong to any of the outlined clusters. Principal component analysis (PCA) shows a similar picture. Two of the Caucasian populations do not follow Hardy-Weinberg expectation, there being a marked deficiency of heterozygotes in arms A, B and C, arguably, due to negative selection of heterozygotes or founder effect. All the obtained data are indicative of the complex genetic structure of Caucasian populations of Ch. “annularius” and total complexity microevolution processes occurring in the Caucasus region.

Karyotypes and COI Gene Sequences of Chironomus annularius Sensu Lato (Diptera, Chironomidae) from Russia, Mongolia, and Armenia

“…Based on the results of cytogenetic analysis, we found that all banding sequences of all studied larvae belong to the chromosome banding pool of C. "annularius" [2,6,10,13]. We found through banding sequences and zygotic combinations that A1.1, A2.2, B1.1, B1.2., C1.1, D1.1, D1.2, D2.2, E1.1, E1.2, E2.2, F2.2, and G1.1 previously were observed in almost all of the studied Palearctic populations except the Nearctic [6,10]. The banding sequence combinations h'annA2 p'annA3 from Yaroslavl and p'annB4.4 from Armenia and Mongolia were previously found only in the South Caucasian (Georgian) population [6].…”

“…In C. "annularius" from Lake Khubsugul in North Mongolia, the Nearctic banding sequence h'annG3 was found in a homozygous state [17]. Recently, the karyotype and chromosomal polymorphism of C. "annularius" were studied in detail in South Caucasian populations, and the banding pool was enriched with new sequences [6]. Researchers of the cytogenetic structure of populations of C. "annularius" noted a high level of chromosomal polymorphism and the presence of endemic sequences in arms A, B, and D, which can affect the phenotypic variability of individuals from different populations [11,13,18].…”

“…One zygotic combination was found in Irkutsk: annA1. All of the banding sequences were described earlier [6][7][8]10]. Some of them were previously found only in the Nearctic populations of C. "annularius", and have some differences from the Palearctic karyotypes.…”

“…Due to several discrepancies between the published descriptions, it was recommended to indicate the source used for identification by applying a name format analogous to, for example, Chironomus «annularius» sensu Strenzke (1959) [1]. The species has a Holarctic distribution [2,[5][6][7], with the type locality situated in West Germany [2,5]. The reliable "species" records known from Russia are the following: Yaroslavl, Saratov, Chelyabinsk, Novosibirsk, Irkutsk Oblast's, Ural, Western Siberia, Altai, Tyva, and Sakha (Yakutia) Republics; Kyrgyzstan (Issyk-Kul Lake); Kazakhstan; Mongolia; North America: USA and Canada [5][6][7].…”

“…The species has a Holarctic distribution [2,[5][6][7], with the type locality situated in West Germany [2,5]. The reliable "species" records known from Russia are the following: Yaroslavl, Saratov, Chelyabinsk, Novosibirsk, Irkutsk Oblast's, Ural, Western Siberia, Altai, Tyva, and Sakha (Yakutia) Republics; Kyrgyzstan (Issyk-Kul Lake); Kazakhstan; Mongolia; North America: USA and Canada [5][6][7].…”