The Evolutionary History of New Zealand Deschampsia Is Marked by Long-Distance Dispersal, Endemism, and Hybridization

SIMPLE SUMMARY: The evolution of the flora of New Zealand has been the subject of many debates, including trans-oceanic dispersal and vicariance. Deschampsia, which is a grass genus distributed in cold–temperate regions of both hemispheres, includes the cosmopolitan D. cespitosa and several endemic species in New Zealand. We applied Restriction Site Associated DNA sequencing, plastid genome, and morphological data to study the evolution of Deschampsia in New Zealand. Native New Zealand D. cespitosa was found in a northern hemisphere clade together with samples of Europe, Canada, Russia, China, Korea, whereas the three endemics were found in a southern hemisphere clade, together with D. antarctica of Argentina and Antarctica. We hypothesize that the endemics diverged from a common ancestor with D. cespitosa in the late Miocene or Pliocene. Hybridization between D. cespitosa and the endemic D. chapmanii was confirmed. Our study qualifies as a model of thorough analyses for a non-model group and provides evidence for the evolutionary history of this widespread genus in New Zealand. ABSTRACT: The contrasting evolutionary histories of endemic versus related cosmopolitan species provide avenues to understand the spatial drivers and limitations of biodiversity. Here, we investigated the evolutionary history of three New Zealand endemic Deschampsia species, and how they are related to cosmopolitan D. cespitosa. We used RADseq to test species delimitations, infer a dated species tree, and investigate gene flow patterns between the New Zealand endemics and the D. cespitosa populations of New Zealand, Australia and Korea. Whole plastid DNA analysis was performed on a larger worldwide sampling. Morphometrics of selected characters were applied to New Zealand sampling. Our RADseq review of over 55 Mbp showed the endemics as genetically well-defined from each other. Their last common ancestor with D. cespitosa lived during the last ten MY. The New Zealand D. cespitosa appears in a clade with Australian and Korean samples. Whole plastid DNA analysis revealed the endemics as members of a southern hemisphere clade, excluding the extant D. cespitosa of New Zealand. Both data provided strong evidence for hybridization between D. cespitosa and D. chapmanii. Our findings provide evidence for at least two migration events of the genus Deschampsia to New Zealand and hybridization between D. cespitosa and endemic taxa.