GEOGRAPHIC-VARIATION IN THE POLYTENE CHROMOSOME-BANDING PATTERN OF THE HOLARCTIC MIDGE CHIRONOMUS (CAMPTOCHIRONOMUS) TENTANS (FABRICIUS)

Polytene chromosomes of Chironomus (Camptochironomus) tentans from Eur ope, Siberia, and North America were examined to clarify genetic relat ionships among widely distributed populations of this Holarctic midge. This first extensive cytogenetic analysis of Siberian populations con firms earlier suppositions that C. tentans karyotypes are quite unifor m across the Palearctic from western Europe to Yakutia. Greater differ ences exist among North American populations in Minnesota, Michigan, a nd Massachusetts, and as a group, these Nearctic populations share so few banding sequences with Palearctic C. tentans that recognition of d iscrete 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 n otation. In total, 42 inversion sequences were found in the 18 Siberia n populations examined, 15 of which were previously undescribed. Of th e 19 sequences found in the three American populations studied, only 6 were shared with the Palearctic. Three of the seven chromosome arms i n Nearctic C. tentans had no sequences in common with European populat ions and four shared none with Siberian populations.