Evolutionary pathways of the tirant LTR retrotransposon in the Drosophila melanogaster subgroup of species.

Tirant, a LTR retrotransposon with copies scattered over the chromosome arms of Drosophila melanogaster, is in the process of being lost from the chromosome arms of most natural populations of the sister species D. simulans. In an attempt to clarify the dynamics and evolution of tirant, we have studied the regulatory and reverse transcriptase regions in copies of the nine closely related species of the D. melanogaster subgroup. We show that tirant is mainly vertically transmitted in these species, with the exception of a horizontal transfer event from an ancestor of D. melanogaster to D. teissieri. We propose that, in four of the species (D. melanogaster, D. simulans, D. sechellia, and D. mauritiana), the observed patterns of evolution of the regulatory region vary with genome constraints and with the history and biogeography of the species.