Geographic variation in the polytene chromosome banding pattern of the Holarctic midgeChironomus(Camptochironomus)tentans(Fabricius)

Abstract

Polytene chromosomes of Chironomus (Camptochironomus) tentans from Europe, Siberia, and North America were examined to clarify genetic relationships among widely distributed populations of this Holarctic midge. This first extensive cytogenetic analysis of Siberian populations confirms earlier suppositions that C. tentans karyotypes are quite uniform across the Palearctic from western Europe to Yakutia. Greater differences exist among North American populations in Minnesota, Michigan, and Massachusetts, and as a group, these Nearctic populations share so few banding sequences with Palearctic C. tentans that recognition of discrete sibling species on each contintent is warranted. Photomaps of polytene chromosomes for both Palearctic and Nearctic sibling species are presented, and banding sequences are described with standardized notation. In total, 42 inversion sequences were found in the 18 Siberian populations examined, 15 of which were previously undescribed. Of the 19 sequences found in the three American populations studied, only 6 were shared with the Palearctic. Three of the seven chromosome arms in Nearctic C. tentans had no sequences in common with European populations and four shared none with Siberian populations.