Genomic Stability in the Galapagos Scalesia Adaptive Radiation: Consistent Transposable Element Accumulation Despite Hybridization and Ecological Niche Shifts

Transposable elements (TEs) have been hypothesized to play a pivotal role in driving diversification by facilitating the emergence of novel phenotypes and the accumulation of divergence between species. The rapid speciation and ecological diversification characteristic of adaptive radiations offer a unique opportunity to examine the link between TE accumulation and speciation, diversification and adaptation. Here, focusing on all 15 species of the genus Scalesia (Asteraceae), a radiation endemic to the Galapagos Islands, we test whether hybridization or shifts in ecological niche are associated with changes in TE accumulation in genomes. Our analyses reveal little to no variation in TE accumulation among Scalesia species nor its hybrid populations. Shifts in ecological niches, linked to climatic variation, did not result in discernible changes in TE accumulation, a surprising finding given the anticipated selective pressure imposed by aridity, a factor often linked to genome size reduction. We found no distinct patterns in the temporal accumulation of TEs, with the exception of a taxon (var. atractyloides) of Scalesia atractyloides. Our findings challenge the assertion that TEs have directly driven diversification, speciation and local adaptation. Instead, TEs may simply be 'along for the ride,' rather than actively contributing to plant diversification. ### Competing Interest Statement The authors have declared no competing interest.