Cytogenetic analysis of a hybrid, Glyptotendipes pallens Mg. x Glyptotendipes glaucus Mg. (Diptera, Chironomidae):: evolutionary considerations

The karyotype of experimentally obtained hybrids between the two closely related species Glyptotendipes pallens and Glyptotendipes glaucus is described, Hybridization was successful in one direction only (G. pallens female x G. glaucus male) The polytene chromosomes AB and EF of the hybrid show a more or less intimate pairing throughout their length. In the chromosomes CD in which an inversion occurs the characteristic loop is formed. The homologues of chromosome G are almost completely asynaptic. The localization of centromere heterochromatin was also studied. Centromere heterochromatin as well as intercalary heterochromatin could be observed in all chromosomes. By C banding analyses it could be shown that G. pallens has a telomeric chromosome G while in G. glaucus it is acrocentric. According to karyotype similarity it can be assumed that these two species have quite recently derived from a common ancestor since they still share much of their genomic organization. On the Black Sea coast (southeast part of Bulgaria) a natural hybridization zone between the sympatric species G. pallens and G. glaucus has been detected. The idea that hybridization between the two species might finally proceed to the formation of a new species by hybrid origin and introgression is discussed.