Multiple horizontal transfer events of a DNA transposon into turtles, fishes, and a frog

Horizontal transfer of transposable elements (HTT) has been reported across many species and the impact of such events on genome structure and function has been well described. However, few studies have focused on reptilian genomes, especially HTT events in Testudines (turtles). Here, as a consequence of investigating the repetitive content of Malaclemys terrapin terrapin (Diamondback turtle) we found a high similarity DNA transposon, annotated in RepBase as hAT-6_XT, shared between other turtle species, ray-finned fishes, and a frog. hAT-6_XT was notably absent in reptilian taxa closely related to turtles, such as crocodiles and birds. Successful invasion of DNA transposons into new genomes requires the conservation of specific residues in the encoded transposase, and through structural analysis, these residues were identified indicating some retention of functional transposition activity. We document six recent independent HTT events of a DNA transposon in turtles, which are known to have a low genomic evolutionary rate and ancient repeats. Malaclemys terrapin terrapin (Diamondback turtle). Malaclemys terrapin pileata (Mississippi diamondback terrapin turtle). Trachemys scripta elegans (Red-eared slider turtle). Chrysemys picta bellii (Western painted turtle). Dermatemys mawii (Hickatee turtle). Sternotherus odoratus (Common musk turtle). Mesoclemmys tuberculata (Tuberculate Toad-headed turtle). Etheostoma spectabile (Orangethroat darter fish). Thalassophryne amazonica (Prehistoric monster fish). Scophthalmus maximus (Turbot fish). Syngnathus acus (Greater pipefish). Scleropages formosus (Asian Arowana fish). Xenopus tropicalis (Western clawed frog).