Parallel ddRAD and Genome Skimming Analyses Reveal a Radiative and Reticulate Evolutionary History of the Temperate Bamboos.

Rapid evolutionary radiations are among the most challenging phylogenetic problems, wherein different types of data (e.g., morphology, molecular) or genetic markers (e.g., nuclear, organelle) often yield inconsistent results. The tribe Arundinarieae i.e., the temperate bamboos, is a clade of tetraploid originated 22 million years ago and subsequently radiated in East Asia. Previous studies of Arundinarieae have found conflicting relationships and/or low support. Here, we obtain nuclear markers from ddRAD data for 213 Arundinarieae taxa and parallel sampling of chloroplast genomes from genome-skimming for 147 taxa. We first assess the feasibility of using ddRAD-seq data for phylogenetic estimates of paleopolyploid and rapidly radiated lineages, optimize clustering thresholds and analysis workflow for orthology identification. Reference-based ddRAD data assembly approaches perform well and yield strongly supported relationships that are generally concordant with morphology-based taxonomy. We recover five major lineages, two of which are notable (the pachymorph and leptomorph lineages), in that they correspond with distinct rhizome morphologies. By contrast, the phylogeny from chloroplast genomes differed significantly. Based on multiple lines of evidence, the ddRAD tree is favored as the best species tree estimation for temperate bamboos. Using a time-calibrated ddRAD tree we find that Arundinarieae diversified rapidly around the mid-Miocene corresponding with intensification of the East Asian monsoon and the evolution of key innovations including the leptomorph rhizomes. Our results provide a highly resolved phylogeny of Arundinarieae, shed new light on the radiation and reticulate evolutionary history of this tribe, and provide an empirical example for the study of recalcitrant plant radiations.