Historical adaptation to transposable element invasions in Drosophila is primarily due to insertions in existing piRNA clusters

In Drosophila simulans, piRNA targeting of three recently invading transposable elements (P-element, Shellder, Spoink) comes mostly from pre-existing piRNA clusters, with 22 strains showing highly polymorphic cluster insertions.

• Why it matters: TE invasions can evade sequence-specific silencing, but it is unclear how the piRNA pathway adapts to new TE threats across host populations.
• What they did: The study assembled genomes from 22 D. simulans strains, annotated piRNA-producing loci, and mapped insertions of the invading TEs within those loci to track where TE-targeting piRNAs originate.
• The result: Resistance to each TE appears to evolve largely independently across strains via distinct insertion events, though some loci like flamenco for Shellder are recurrent targets, implying both inherited and de novo piRNA cluster contributions.

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