On microgeographic differentiations of a chromosomal polymorphism in Chironomus plumosus L. from Lake Tystrup‐Bavelse, Denmark (Diptera: Chironomidae)

Abstract

The inversion polymorphisms in larvae of the midge Chironomus plumosus L. from 10 stations in Lake Tystrup‐Bavelse were followed during two years (1977–1979). A comparison of the frequencies of the three homologous genotypes St/St‐St/BII‐BIIBII from different parts of the lake shows that stations with the greatest depths have the highest St/BII‐frequencies during the spring. At the same time these stations exhibit excesses of the mentioned heterokaryotype compared to the Hardy‐Weinberg distribution. The mentioned inversion is in all probability sustained by the superiority of the heterozygote St/BII in the part of the lake called Lake Tystrup. In samples from Lake Bavelse there were almost agreement between the observed and the expected numbers of the three genotypes in question (based on the Hardy‐Weinberg distribution). Differences in the genotype frequencies and in the contrivances of the polymorphisms show that the two parts of Lake Tystrup‐Bavelse have two separate populations, without recognizable gene‐flow. Copyright © 1986, Wiley Blackwell. All rights reserved