Horizontal transfer of Vingi non-LTR retrotransposons in Darwinula stevensoni

Ostracods are microscopic, bi-valved crustaceans with the best fossil record of living arthropods. The non-marine ostracod Darwinula stevensoni is furthermore one of the last remaining examples of an ancient asexual, and likely abandoned sexual reproduction >20 million years ago. Despite the limited genetic diversity of D. stevensoni, its cosmopolitan distribution in different aquatic habitats indicates this species can survive asexually in the long-term. To unravel the novel adaptations that made this possible, the UNTANGLE project is deeply investigating the D. stevensoni genome. Now, four families of the Vingi non-LTR retrotransposons within the D. stevensoni genome were found to be highly identical to those from other species. This suggests Vingi was horizontally transferred between these species, which include turtles, lamprey, and deep-sea tube worms. Vingi consensus sequences were generated for D. stevensoni using Oxford Nanopore and Illumina assemblies, and mapped to >10,000 Metazoan genomes. High-quality mappings will be used to generate species-specific consensus sequences, upon which phylogenetic trees can be based and compared to those of other transposons, as well as with the host phylogenies. HTT will be visible as discorrespondence across phylogenetic trees. In a deeper exploration, the divergence between Vingi copies from each host and their consensus will also be used for the relative aging of their HTT events.

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