Distribution and evolution of mobile elements in the virilis species groupof Drosophila

The distributions of Penelope and Ulysses, two transposable elements that c an induce hybrid dysgenesis, were studied in several species groups of Dros ophila. No significant hybridization to Penelope and Ulysses probes was det ected by Southern blot analyses of species outside the virilis group. In co ntrast, both element families have had a long residence in all species of t he virilis species group, as indicated by their strong presence in the hete rochromatic chromocenter. Except for D. kanekoi, D. lummei, and some strain s of D. virilis, species of the group carry full-sized, and at least potent ially functional, copies of both element families. Consistent with the occu rrence of recent transposition, Penelope and Ulysses elements are located a t different chromosomal sites in different geographical strains of the same species. A total of 79 Penelope and 47 Ulysses euchromatic insertion sites were localized to chromosomal subsections in species of the virilis group. Highly significant deviations from independence of the distributions of Pe nelope and Ulysses and previously established inversion breakpoints were do cumented, suggesting that these transposable elements may have played an im portant role in genomic reorganization and evolution of the virilis species group, which is especially rich in karyotypic variation.