Horizontal transfer and the widespread presence of Galileo transposons in Drosophilidae (Insecta: Diptera)

Galileo is a transposon notoriously involved with inversions in Drosophila buzzatii by ectopic recombination. Although widespread in Drosophila, little is known about this transposon in other lineages of Drosophilidae. Here, the abundance of the canonical Galileo and its evolutionary history in Drosophilidae genomes was estimated and reconstructed across genera within its two subfamilies. Sequences of this transposon were masked in these genomes and their transposase sequences were recovered using BLASTn. Phylogenetic analyses were employed to reconstruct their evolutionary history and compare it to that of host genomes. Galileo was found in nearly all 163 species, however, only 37 harbored nearly complete transposase sequences. In the remaining, Galileo was found highly fragmented. Copies from related species were clustered, however horizontal transfer events were detected between the melanogaster and montium groups of Drosophila, and between the latter and the Lordiphosa genus. The similarity of sequences found in the virilis and willistoni groups of Drosophila was found to be a consequence of lineage sorting. Therefore, the evolution of Galileo is primarily marked by vertical transmission and long-term inactivation, mainly through the deletion of open reading frames. The latter has the potential to lead copies of this transposon to become miniature inverted-repeat transposable elements.