Format: ORAL

Nora Walden1, Christiane Kiefer1, Marcus A. Koch1

1 Department of Biodiversity and Plant Systematics, Centre for Organismal Studies, University of Heidelberg, Heidelberg, Germany

The Arabideae represent the largest Brassicaceae tribe with ~550 species in 18 genera, among them eponymous Arabis and the large genus Draba with over 400 species. Polyploidy is prevalent in the tribe, with ploidy levels up to hexadecaploid, and hybridization is hypothesized to be common. Previous phylogenetic studies have identified larger clades consistently, but failed to provide resolution at the species level, in part likely due to the presence of paralogs remaining from past whole-genome duplications (WGDs) and hybridizations. We have developed a concept and workflow to infer polyploidization status from target enrichment data and reconstruct the evolutionary history of the taxa of interest using evolutionary placement of paralogs into a diploid reference tree. This method allows us to use information from paralogs despite multiple rounds of WGD and hybridization. Our results provide a solid backbone phylogeny for the Arabideae and pinpoint the ancestral lineages involved in past hybridizations. Within Draba, we found strong evidence that one of three main evolutionary lineages originated from hybridization between the other two lineages, with subsequent hybridizations giving rise to further subclades. In total we identified 68% of our samples as ancient polyploids and clustered them in over 40 clades with different patterns of paralog placement, suggesting independent or additional WGDs and hybridization events. Our study highlights the need for novel approaches to phylogenomics in clades with complex evolutionary histories.