Atypical landscape of transposable elements in the large genome of Aedes aegypti

Transposable elements (TEs) contribute significantly to variation in genome size among eukaryotic species, but the factors influencing TE accumulation and diversification are only partially understood. Most of our current knowledge about TE organization, dynamics and evolution derives from investigations in model organisms with a relatively small genome size such as Drosophila melanogaster or Arabidopsis thaliana. Whether the observed patterns hold true in larger genomes remains to be determined. The Diptera order is an ideal taxon to address this question, because it includes a forty-year model of TE biology (D. melanogaster) as well as mosquito species with significantly larger genomes. Here, we use a comparative genomics approach to characterize the genomic forces that have shaped the TE content of the Aedes aegypti genome (1.3 Gb) relative to the Anopheles coluzzii genome (300 Mb) and the D. melanogaster genome (180 Mb). Leveraging a newly developed high-quality TE library for Ae. aegypti, our results reveal a contrasted pattern of TE organization in Ae. aegypti compared to An. coluzzii and D. melanogaster. Our analyses suggest that the substantial TE fraction observed in the Ae. aegypti genome reflect both a high rate of TE transposition and a low rate of TE elimination. Together, our results indicate that TE organization and evolutionary dynamics in the large genome of Ae. aegypti are distinct from those of other dipterans with smaller genomes.