The role of whole-genome duplication (WGD) in facilitating shifts into novel biomes remains unknown. Focusing on two diverse woody plant groups in New Zealand, Coprosma (Rubiaceae) and Veronica (Plantaginaceae), we investigate how biome occupancy varies with ploidy level, and test the hypothesis that WGD increases the rate of biome shifting. Ploidy levels and biome occupancy (forest, open and alpine) were determined for indigenous species in both clades. The distribution of low-ploidy ( Coprosma : 2 x , Veronica : 6 x ) versus high-ploidy ( Coprosma : 4–10 x , Veronica : 12–18 x ) species across biomes was tested statistically. Estimation of the phylogenetic history of biome occupancy and WGD was performed using time-calibrated phylogenies and the R package BioGeoBEARS. Trait-dependent dispersal models were implemented to determine support for an increased rate of biome shifting among high-ploidy lineages. We find support for a greater than random portion of high-ploidy species occupying multiple biomes. We also find strong support for high-ploidy lineages showing a three- to eightfold increase in the rate of biome shifts. These results suggest that WGD promotes ecological expansion into new biomes.
Metrosideros (Myrtaceae) comprises 58 woody species distributed across Oceania and with three singleton outliers in Philippines, South America and Africa. Centres of species richness occur in New Zealand and New Caledonia. This distribution accords with a proposed Gondwanan origin for the family. While the phylogeography of one component of the genus – subgenus Metrosideros – has received some examination, the rest of the genus has not been resolved. In this study, we improve resolution of the phylogeny of Metrosideros and consider origin, possible vicariant relationships, long‐distance dispersal events and dispersal routes for the genus. A Bayesian phylogeny, with all but one recently described species of Metrosideros, was constructed using concatenated ITS + ETS rDNA from samples we collected and sequenced. Relative to previous work on Metrosideros using ITS alone, here, using ITS plus ETS, we produce a more detailed and robust phylogeny with a near threefold increase in significant nodal support. Putative centres of origin/diversification, vicariant events and dispersals were considered with reference to the phylogeny, present‐day diversity and fossil record of Metrosideros. Metrosideros occurs as five clades, including the former genera Tepualia and Carpolepis. The paraphyletic and now superseded subgenus Mearnsia included elements of four of these clades, whereas subgenus Metrosideros forms a single clade with robust support. Our phylogeography indicates multiple dispersal/vicariant events within the history of the genus, a number of which involved New Zealand. Among other such events, we infer an exceptional 6300 km trans‐equatorial dispersal from Fiji to the Bonin Islands (Japan). Australia and New Zealand, respectively, are the likely landmasses of origin and diversification for Metrosideros. Typical patterns of floral dispersal proceed from large continental landmasses onto increasingly remote islands and with distance from continent species diversity usually declines. However, Metrosideros shows a countervailing pattern since relatively remote islands are the main centres of speciation and dispersal.
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