Divergent cytogenetic evolution in Nearctic and Palearctic populations of sibling species in Chironomus (Camptochironomus) Kieffer

Abstract

Chromosomal polymorphism is described for natural populations of Chironomus pallidivittatus in both the Palearctic and Nearctic regions. The Palearctic populations studied exhibit 24 banding sequences, whereas 10 banding sequences have been recorded from Nearctic C. pallidivittatus. In total, 29 sequences and 37 genotypic combinations have been found. Of the 29 sequences known, only 5 are Holarctic (common to both the Nearctic and Palearctic), 19 are exclusively Palearctic, and 5 are Nearctic. The karyotype of Nearctic C. pallidivittatus is characterized by specific, homozygous Nearctic sequences in arms B and G and fixed Holarctic inversion sequences in the other arms. Only two chromosome arms in C. pallidivittatus, but all seven arms in the sibling species Chironomus tentans, differ between Palearctic and Nearctic forms by the presence of unique, homozygous sequences in the Nearctic karyotype. This indicates a great difference in the cytogenetic histories of these closely related species; much less karyotypic divergence between continents has occurred in C. pallidivittatus than in C. tentans. The cytogenetic distance between Palearctic and Nearctic populations of C. tentans is higher (DN = 1.62) than in C. pallidivittatus (DN = 0.27). Thus, Palearctic and Nearctic C. tentans should be regarded as sibling species, but Palearctic and NearcticC. pallidivittatus are best viewed as strongly divergent races of the same species. A photomap of polytene chromosomes of C. pallidivittatus is presented in which banding sequences are mapped by using C. tentans as a standard.

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

“…The species marked by small letters were obtained from Hankeln et al (1997). logical data are used. On the other hand, karyological analysis is well suited to the comparison of closely related species and populations (e.g., Martin, 1979;Michailova, 1987;Kiknadze et al, 1998). Thus, an integrated approach including morphological, cytological, and molecular-biological techniques is most fruitful for the investigation of chironomid evolution.…”

Population variability in Chironomus (Camptochironomus) species (Diptera, Nematocera) with a Holarctic distribution: evidence of mitochondrial gene flow

“…Recent cytogenetic studies of Holarctic Chironomus species (Kiknadze et al ., 1996, 1998, 2000; Butler et al ., 1999) have revealed markedly different levels of differentiation between Nearctic and Palearctic populations in different species. Some species, such as C. thummi , have essentially the same banding pattern of the polytene chromosomes on both continents (J. Martin, unpublished list of North American Chironomus ‐species, http://www.genetics.unimelb.edu.au /Martin2/NACytfiles/NAChiron.html).…”

“…C. pallidivittatus , another sibling species of C. tentans (s.l. ), has differentiated to a much lesser extent in the two continents (Kiknadze et al ., 1998). There is, however, no evidence whether such differences in the level of differentiation could be attributed to migration at different times or to different rates of cytological evolution in the various species.…”

Cytogenetic characteristics of species of the Chironomus genus (Diptera, Chironomidae) from Lake Łuknajno Biosphere Reserve (northwest Poland)

“…Usually, species identification is studied only based on the external morphology of the specimen (Kownacki 1999). Because the majority of the species do not differ in their external morphology at the larval stage, species identification within this family is based mainly on the karyotype characteristics of the salivary gland chromosomes (Keyl 1962, Wülker and Butler 1983, Michailova 1989, Kiknadze et al 1991, Kiknadze et al 1998. Therefore, it is only possible that similar species can be identified using species-specific cytogenetic markers.…”