Biogeography and evolution of flowering plants in the American West: Gaillardia (Asteraceae) and Synthyris (Plantaginaceae).

摘要

This study explores the biogeography of flowering plants in the American West. We examine the biogeography of both the low elevation, largely xeric-adapted Gaillardia (Asteraceae) that radiated out of the Chihuahuan Desert and two clades of the cool-adapted Synthyris (Plantaginaceae) that diversified in mountain environments. We examine evolutionary processes concerning range shifts and consider how climate changes have influenced the distribution of organisms in the American West.; We used phylogeny reconstructions based on DNA sequences from nuclear ribosomal internal and external transcribed spacers and plastid trnT-trnF regions to infer sister group relationships and identify the geographic origin and avenues of range expansion in North American Gaillardia . Phylogenetic analyses recovered three previously hypothesized sections and well supported clades associated with particular geographic regions. Dispersal-Vicariance Analysis reconstructed a Chihuahuan Desert origin and major range expansions eastward into central Texas and along the Gulf Coast, northwest into Arizona and the Intermountain region, and northward onto the Great Plains and along the Rocky Mountains.; We used phylogeography to infer modes of speciation and migration patterns in two clades of Synthyris. The Southern Rocky Mountain clade of S. sect. Besseya is distributed in the Southern Rocky Mountains and S. sect. Dissecta is centered in the Northern Rocky Mountains with Olympic Mountains disjuncts. Both clades have species currently restricted to high elevation interglacial refugia. We used plastid DNA trnT-trnL and psbA-trnH intergenic spacer sequences to infer haplotypes for phylogeographic analyses. Haplotype distributions in both clades were consistent with broad scale gene flow in their ancestral lineages with subsequent random capture of haplotypes in widespread populations. Disjunctions in both sections were likely caused by fragmentation of formerly widespread populations. Genetic signatures were consistent with widespread migration in the southern clade especially in the lower elevation species, whereas we found evidence of more isolation in S. sect. Dissecta. In both clades we found evidence consistent with speciation following peripheral isolation, and in the southern clade we find evidence consistent with a hypothesis of allopolyploid speciation. We infer that Pleistocene glaciations played an important role in species origins and shaping extant distributions in alpine Synthyris.