A scenario for the hobo transposable element invasion, deduced from the structure of natural populations of Drosophila melanogaster using tandem TPE repeats

Temporal surveys of hobo transposable elements in natural populations revea l a historical pattern suggesting a recent world-wide invasion of D. melano gaster by these transposons. perhaps following a recent horizontal transfer . To clarify the dynamics of hobo elements in natural populations, and thus to provide further data for our understanding of the hobo invasion, TPE ta ndem repeats, observed in the polymorphic S region of the element, were use d as molecular markers. The number of TPE repeats was studied in 101 curren t populations from around the world, and in 63 strains collected in the pas t. This revealed a geographical distribution which seems to have been stabl e since the beginning of the 1960s. This distribution is compatible with a number of hypotheses for the dynamics of hobo elements. We propose a scenar io based on an invasion in two stages: first, a complete invasion by elemen ts with three TPE repeats, followed by the beginning of a new invasion invo lving hobo elements with five or seven repeats.