Understanding why biotic diversity differs among geographic regions is a fundamental challenge in evolutionary biology and ecology. This research will combine phylogenetic analyses with biogeography and ecology to examine diversification of the bluebell genus, Mertensia, which has its greatest species richness in western North America but also occurs in Asia. The research aims to: (1) produce the first molecular phylogeny for Mertensia; (2) test for the ancestral area of Mertensia; (3) estimate the time of Mertensia?s origin and identify shifts in diversification; and (4) test for effects of geographic and ecological change on diversification rates. Chloroplast DNA sequences will be used to reconstruct a phylogenetic hypothesis of species relationships. A time-calibrated phylogeny will be used to test hypotheses of geographic and ecological change. This research will help explain the ecological and geographical dynamics of plant diversification and have implications for understanding effects of anthropogenic climate change. Results will be published in peer-reviewed journals, presented at scientific meetings, and deposited in online databases. Outreach from this research will be directed toward native plant societies, popular periodicals, and work with the National Girls Collaborative Project, sponsored by the STEM Education Coalition.
This study explored the taxonomy, systematics, and biogeography of Mertensia. Mertensia is a monophyletic genus of herbaceous perennials that comprises 62 species in Asia, Beringia, North America, and circumboreal locales, with a geographic center of diversity in the western United States. The phylogenetic relationships of Mertensia have been uncertain, with placement in various tribes in subfamily Boraginoideae. Moreover, Mertensia has presented considerable taxonomic problems especially centered in broadly circumscribed taxa. Using a phylogenetic approach, we evaluated relationships within Boraginaceae, inferred evolutionary lineages, and addressed problematic taxonomic circumscriptions. We applied DNA sequence data to a broad sampling of Boraginaceae and found strong support for the monophyly of Mertensia and Asperugo as its sister. Mertensia was strongly supported as a member of the tribe Cynoglosseae in Boraginoideae. Phylogenetic reconstructions using eleven chloroplast markers recovered three deep clades in Mertensia that included: (1) Asian taxa, a Beringian subclade, and a circumboreal subclade; (2) the Beringian M. rivularis; and (3) North American taxa. Although we recovered weak support for several deeper nodes in the North American clade, our results provided moderate to strong support for 13 subclades. Notable results include broadly circumscribed taxa (M. ciliata, M. lanceolata, M. oblongifolia, M. viridis) as polyphyletic; we recommend narrow circumscriptions for each of these taxa. Divergence times for Mertensia were estimated with molecular dating methods. Our results derived from the molecular dating analysis of Mertensia recovered signatures of a relatively young lineage that faced rapid diversification over the last 7–10 million years. From biogeographic reconstructions, we inferred the ancestral area to have been Asia or a more widespread distribution encompassing parts of Asia, Beringia, and possibly circumboreal locales. Although its exact place of origin cannot be determined, it seems unlikely that North America, which for Mertensia has greater taxic diversity than Asia, is the ancestral area for the genus. Mertensia likely first appeared in the mid Miocene as a floristic element of boreal, arctic, and alpine habitats and probably remained largely restricted to cool, edaphically moist sites throughout much of its history. Beringia likely played an important role in the early geographic radiation of the genus. Initial range expansion of North American mertensias from Beringia and the Pacific Northwest probably coincided with the onset of extreme cooling and increased topographic diversity in North America during the late Miocene to early Pliocene (7.70–4.22 Ma), followed by the diversification of three deep North American clades (Pacific Northwest clade, Southern Rocky Mountain clade, Central Rocky Mountain clade). Both the Southern Rocky Mountain and Central Rocky Mountain clades used the Rocky Mountains for range expansion from the Pacific Northwest. The Rocky Mountains played an important role in the diversification of these two clades as climatic fluctuations associated with glacial and interglacial cycles of the Pleistocene shifted populations over latitudinal and elevational gradients to shape patterns of distribution and regional diversity observed today. Our results provide important insights into the potential affect of global climate change on Mertensia populations in montane, alpine, and boreal regions of the Northern Hemisphere.
