TE invasion fuels molecular adaptation in laboratory populations of Drosophila melanogaster

Transposable elements are mobile genetic parasites that frequently invade
new host genomes through horizontal transfer. Invading TEs often exhibit a
burst of transposition, followed by reduced transposition rates as
repression evolves in the host. We recreated the horizontal transfer of
P-element DNA transposons into a D. melanogaster host and followed the
expansion of TE copies and evolution of host repression in replicate
laboratory populations reared at different temperatures. We observed that
while populations maintained at high temperatures rapidly go extinct after
TE invasion, those maintained at lower temperatures persist, allowing for
TE spread and the evolution of host repression. We also surprisingly
discovered that invaded populations experienced recurrent insertion of
P-elements into a specific long non-coding RNA, lncRNA:CR43651, and that
these insertion alleles are segregating at unusually high frequency in
experimental populations, indicative of positive selection. We propose
that, in addition to driving the evolution of repression, transpositional
bursts of invading TEs can drive molecular adaptation.