Extensive polyploidization but no obvious role for whole genome duplication in a plant radiation. Diploid radiation despite massive polyploidization

Diversity is not equally distributed across the Tree of Life. Certain groups exhibit an enormous diversity compared to other, often closely related groups: they radiate. Among characters considered as key traits promoting radiations is whole genome duplication (WGD). In particular paleo-WGDs have been demonstrated to occur around the onset of radiations, supposedly co-occurring with events of stress imposed by the environment. In contrast to paleo-WGDs, evidence for increased diversification rates of neopolyploids compared to diploids is controversial in the literature. We chose the southern African clade of the plant genus Oxalis (SoA Oxalis: 230 spp.) to study the role of WGDs on diversification rate shifts. Our analyses were based on a phylogenomic hypothesis using the Hyb-Seq approach (122 spp., 1.1 Mb nuclear DNA per accession, >1,100 loci, near-complete plastomes), which has the potential to resolve phylogenies of radiating groups better than traditional methods. We first estimated the frequency of WGDs in SoA Oxalis, then tested if WGDs are overrepresented in particular clades, and finally tested if WGD corresponds with an increase or decrease in net diversification rate. We found an exceptionally high frequency of polyploids in SoA Oxalis, and diploids showed significantly higher net diversification rates compared to polyploids. Remarkably, WGDs play no obvious role in this plant radiation.