Studying transposable elements in lesser-explored branches of life is essential to understand their distribution and evolutionary dynamics. Over the past years, our investigation into the diversity of LTR‑retrotransposons in crustaceans, mollusks, and annelids has enabled us to establish the classification of LTR-retrotransposons into several clades per superfamily, while also revealing strong differences in their distribution. Copia elements appear rare and relatively homogenous in these three taxa, whereas Gypsy elements are detected in a considerable number of copies and exhibit high diversity. BEL/Pao elements show an intermediate behavior.

To complete our exploration of LTR-retrotransposons spread in metazoans, we characterized them in 263 well-assembled genomes covering most of this realm. Based on the phylogeny of RT/RNaseH domain, we annotated each superfamily of elements to the clade level. Our observations revealed differences between taxa. For instance, no Copia or BEL/Pao elements were detected in turtles' genomes, while serpents exhibited a particularly high number of elements. Although Gypsy elements analysis is ongoing, we have already identified several new clades in Copia and BEL/Pao and characterized the distribution of existing clades in metazoans. These clades exhibit various distributions, and surprisingly, our results indicate a strong influence of environment (marine vs terrestrial) on the Copia clade repartition. This suggests a role of horizontal transfers in the evolutionary dynamics of these elements.