Genomes of historical specimens reveal multiple invasions of LTR retrotransposons in <i>Drosophila melanogaster</i> during the 19th century.

Abstract

Transposable element invasions have a profound impact on the evolution of genomes and phenotypes. It is thus an important open question how often such TE invasions occur. To address this question, we utilize the genomes of historical specimens, sampled about 200 y ago. We found that the LTR retrotransposons Blood, Opus, and 412 spread in <i>Drosophila melanogaster</i> in the 19th century. These invasions constitute second waves, as degraded fragments were found for all three TEs. The composition of Opus and 412, but not of Blood, shows a pronounced geographic heterogeneity, likely due to founder effects during the invasions. Finally, we identified species from the <i>Drosophila simulans</i> complex as the likely origin of the TEs. We show that in total, seven TE families invaded <i>D. melanogaster</i> during the last 200y, thereby increasing the genome size by up to 1.2Mbp. We suggest that this high rate of TE invasions was likely triggered by human activity. Based on the analysis of strains and specimens sampled at different times, we provide a detailed timeline of TE invasions, making <i>D. melanogaster</i> the first organism where the invasion history of TEs during the last two centuries could be inferred.