DISSERTATION RESEARCH: Selenium hyperaccumulation in a rapid radiation of legumes

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Milkvetch (Neo-Astragalus) species from the legume plant family known as selenium hyperaccumulators are restricted to soils rich in the element selenium, where they accumulate the element in their tissues at levels that are toxic to other organisms. This research will determine the number of origins of selenium hyperaccumulation in milkvetch species by reconstructing the group's evolutionary history using DNA sequence data. The project will also sequence genes thought to be involved in selenium hyperaccumulation to determine if they have been subject to natural selection. This research will provide one graduate student and undergraduates with training in molecular, chemical, and bioinformatics techniques and will also supply molecular resources for population genetic studies of poorly known North American Astragalus species.Twenty-five Neo-Astragalus species from two traditional taxonomic groups have been identified as selenium hyperaccumulators; however, it is not known if these groups are monophyletic. The researchers will sample these selenium hyperaccumulators and other species from across the clade and reconstruct a phylogeny using a target-enrichment approach for sequencing low-copy nuclear loci in order to infer the number of times selenium hyperaccumulation has evolved. Analytical chemistry methods will be used to survey selenium accumulation in relevant species, and phylogenetic ancestral state reconstruction will be used to characterize the number of origins of selenium hyperaccumulation from the resulting phylogeny. This approach can quantify the relative contribution of ecologically driven speciation and allopatric speciation in light of the number of origins of the cryptic trait, their phylogenetic position, and geographic ranges of the different species.