Invasion of Drosophila virilis by the Penelope transposable element

The Penelope family of transposable elements (TEs) is broadly distributed in most species of the virilis species group of Drosophila. This element plays a pivotal role in hybrid dysgenesis in Drosophila virilis, in which at least four additional TE families are also activated. Here we present evidence that the Penelope family of elements has recently invaded D. virilis. This evidence includes: (1) a patchy geographical distribution, (2) genomic locations mainly restricted to euchromatic chromosome arms in various geographical strains, and (3) a high level of nucleotide similarity among members of the family. Two samples from a Tashkent (Middle Asia) population of D. virilis provide further support for the invasion hypothesis. The 1968 Tashkent strain is free of Penelope sequences, but all individuals collected from a 1997 population carry at least five Penelope copies. Furthermore, a second TE, Ulysses, has amplified and spread in this population. These results provide evidence for the Penelope invasion of a D. virilis natural population and the mobilization of unrelated resident transposons following the invasion.