Phylogenetics and phylogeography of the South Pacific alpine plant Oreomyrrhis: Insights into global alpine biogeography

Alpine vegetation worldwide constitutes the alpine ecosystem, the only terrestrial biome that is distributed across a large latitudinal gradient and reaches a global distribution. Plant groups distributed in multiple alpine systems thus present an excellent system to test biogeographic hypotheses on a global scale. In this dissertation, phylogenetics and phylogeography of Oreomyrrhis are studied to elucidate its controversial phylogenetic relationships within the family Apiaceae and the historical biogeographic mechanisms that generated its disjunct distribution in the southern portion of the Pacific Basin (Mesoamerica, Andes, southern Patagonia, Tierra del Fuego, Falklands, New Zealand, SE Australia, Tasmania, New Guinea, Borneo, and Taiwan).; Analyses of nuclear ITS sequences unambiguously place Oreomyrrhis in the subtribe Scandicinae (tribe Scandiceae) and suggest its intimate relationship with the North American species of the otherwise Eurasian genus Chaerophyllum. Analyses of the combined data set composed of ITS and two chloroplast intergenic spacers (trnS-trnG and atpB-rbcL) further confirm the monophyly of Oreomyrrhis and its sister taxon relationship with the North American Chaerophyllum . This well-established phylogenetic relationship strongly supports synonymizing Oreomyrrhis taxa with Chaerophyllum .; The star-like haplotype network structure in all three data sets (ITS, trnS-trnG, and atpB-rbcL) suggests a scenario of recent population range expansion, an inference consistent with the significant negative value of the Tajima's D. The existence of two widespread interior/ancestral haplotypes in atpB-rbcL data suggests that multiple dispersal events have occurred. Coupled with results of phylogenetic analyses and molecular dating, the South Pacific disjunction of Oreomyrrhis is clearly a result of recent long-distance dispersal, most likely during the late Pliocene to the early Pleistocene. The weakly supported sister-taxon relationship between the SW Pacific clade (New Guinea and Borneo) and the rest of Oreomyrrhis suggests that this region is a possible center of origin for Oreomyrrhis, a proposition also consistent with the distribution of ancestral haplotypes in the network. However, Australia harbors the highest genetic diversity and most ancestral haplotypes, suggesting its possibility also as a center of origin.; These findings corroborate many recent studies, suggesting that long-distance dispersal in recent geological time (Pliocene-Pleistocene) has been the dominant mechanism generating the disjunctions of the South Pacific alpine taxa.