Chromosome Comparisons of Australian Scaptodrosophila Species

SIMPLE SUMMARY: Scaptodrosophila are a diverse group of flies that are widespread in Australia but have received limited research attention. In this study, we characterized the chromosomes of 12 Scaptodrosophila species. We found that the structural changes in their chromosomes are very similar to those seen in Drosophila, a related genus of flies. This includes the amplification of repetitive elements and changes in chromosome length in small (dot) chromosomes and the sex chromosomes. We also found numerous weak points along the arms of polytene chromosomes, which suggest the presence of internal repetitive sequences. Regions producing the nucleolus are at the same chromosome positions in Scaptodrosophila and Drosophila. These chromosomal studies provide a foundation for future genetic studies in Scaptodrosophila flies. ABSTRACT: The Scaptodrosophila represent a diverse group of Diptera closely related to Drosophila. Although they have radiated extensively in Australia, they have been the focus of few studies. Here, we characterized the karyotypes of 12 Scaptodrosophila species from several species groups and showed that they have undergone similar types of karyotypic change to those seen in Drosophila. This includes heterochromatin amplification involved in length changes of the sex and ‘dot’ chromosomes as well as the autosomes, particularly in the coracina group of species. Numerous weak points along the arms of the polytene chromosomes suggest the presence of internal repetitive sequence DNA, but these regions did not C-band in mitotic chromosomes, and their analysis will depend on DNA sequencing. The nucleolar organizing regions (NORs) are at the same chromosome positions in Scaptodrosophila as in Drosophila, and the various mechanisms responsible for changing arm configurations also appear to be the same. These chromosomal studies provide a complementary resource to other investigations of this group, with several species currently being sequenced.