Spoink, a LTR retrotransposon, invaded D. melanogaster populations in the 1990s.

During the last few centuries D. melanogaster populations were invaded by several transposable elements, the most recent of which was thought to be the P-element between 1950 and 1980. Here we describe a novel TE, which we named Spoink, that has invaded D. melanogaster. It is a 5216nt LTR retrotransposon of the Ty3/gypsy superfamily. Relying on strains sampled at different times during the last century we show that Spoink invaded worldwide D. melanogaster populations after the P-element between 1983 and 1993. This invasion was likely triggered by a horizontal transfer from the D. willistoni group, much as the P-element. Spoink is probably silenced by the piRNA pathway in natural populations and about 1/3 of the examined strains have an insertion into a canonical piRNA cluster such as 42AB. Given the degree of genetic investigation of D. melanogaster it is perhaps surprising that Spoink was able to invade unnoticed. Author summary: Horizontal transfer of transposable elements (TE) is a major factor driving genome evolution. Yet well documented cases of such horizontal transfer events are rare. Most evidence is indirect, relying on sequence similarity of TEs between species. Based on strains sampled during the last decades we provide direct evidence that the retrotransposon Spoink was absent in worldwide D. melanogaster populations before 1983 but present in populations after 1993. We suggest that the Spoink invasion was triggered by a horizontal transfer from a Drosophila species of the willistoni group. [ABSTRACT FROM AUTHOR]