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 re lated species Glyptotendipes pallens and Glyptotendipes glaucus is describe d, 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 mo re or less intimate pairing throughout their length. In the chromosomes CD in which an inversion occurs the characteristic loop is formed. The homolog ues of chromosome G are almost completely asynaptic. The localization of ce ntromere heterochromatin was also studied. Centromere heterochromatin as we ll as intercalary heterochromatin could be observed in all chromosomes. By C banding analyses it could be shown that G. pallens has a telomeric chromo some G while in G. glaucus it is acrocentric. According to karyotype simila rity it can be assumed that these two species have quite recently derived f rom a common ancestor since they still share much of their genomic organiza tion. On the Black Sea coast (southeast part of Bulgaria) a natural hybridi zation zone between the sympatric species G. pallens and G. glaucus has bee n detected. The idea that hybridization between the two species might final ly proceed to the formation of a new species by hybrid origin and introgres sion is discussed.