Cytogenetics of the genus Dundocoris Hoberlandt (Heteroptera, Aradidae, Carventinae) where chromosome fusion played the dominant role in karyotype evolution

More than 260 individuals belonging to 17 taxa (species and subspecies) of the genus Dundocoris from South Africa were cytogenetically investigated. Of the 17 taxa, six have a chromosome number of 2n(male) = 28XY, six have 2n(male) = 26XY and one each has 2n(male) = 27 X1X2Y, 20XY, 14XY, 9XY(1)Y(2) and 7XY(1)Y(2) respectively. The autosomal karyotypes of all the taxa with 28XY are very similar while the largest autosome of the 26XY taxa varies greatly in size. It is concluded that 2n(6) = 28XY is the ancestral chromosome number of Dundocoris and that it shares this ancestral number with genera like Miteronotus and Trichocarventus. The other chromosome numbers originated from chromosome fusions and 23 fusions, of which four were between autosomes and sex chromosomes, probably took place in the karyotype evolution of the investigated taxa. These are the first recorded cases in the Heteroptera where autosome-sex chromosome fusions gave rise to multiple sex chromosome systems. In D. flavilineatus ndabeniensis an autosome-Y-chromosome fusion presumably gave rise to the 27 X1X2Y karyotype, while an autosome-X-chromosome fusion led to the 9XY1Y2 karyotype of D. nodulicarinus novenus. In D. nodulicarinus septeni. a peculiar 7XY(1)Y(2) karyotype originated from two further fusions between an autosomal pair and the X- and Y-chromosomes respectively. Contrary to the general perception that chromosome fragmentations play a major role in chromosome number variation in Heteroptera, only chromosome fusions occurred in the karyotype evolution of Dundocoris. It was also observed that the sizes of the sex chromosomes often vary significantly between species or conspecific populations. The karyotypes of all 17 Dundocoris taxa from South Africa are described and illustrated by photomicrographs and idiograms and their evolution and relationships are discussed.