Dissertation Research: Phylogeny of Helianthus Including New Methods to Detect Reticulate Evolution

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Project summary for general readers Despite the agronomic and research importance of the genus Helianthus (sunflowers), the evolutionary relationships among the species are still largely unresolved. In addition to H. annuus, the cultivated species of sunflower, the genus contains an additional 48 species that are distributed across North America. The annual species are a model system for studying diploid hybrid speciation - speciation caused by normal sexual hybridization between two species - so their relationships have been closely researched. But relationships among the rest of the species, especially the perennials, are not well understood. This lack of resolution is mostly due mostly to recent rapid speciation and hybrid speciation. Resolving these relationships along with testing the existing parental hypotheses of the perennial hybrid sunflowers will be addressed using (1) a comparatively faster evolving marker; (2) tools for reconstructing reticulate evolution (an evolutionary history that has evolved in a net-like fashion, due to hybridization, instead of a tree-like pattern); and (3) multiple nuclear markers. Currently the number of nuclear markers that are accessible for inferring phylogenetic history is very limited. Our goal at the end of this project is to provide the plant systematic community with a set of universal nuclear primers for plants. In conjunction with colleagues in The Department of Computer Sciences, a comparative analysis of two entire plant genomes (Oryza and Arabidopsis) has produced a series of primer pairs that are conserved between these genomes. Using these primer pairs 18 plants are being screened across a wide taxonomic sampling: six species in Helianthus, six in Phalaenopsis (an orchid), and six that span other flowering plant groups. Data collected from these markers will be used with the new algorithms for reconstructing reticulate evolution and together these methods will be tested on the known parentage of the annual hybrid sunflowers. If these methods correctly infer these relationships then they will be applied more broadly to the less-studied perennial sunflowers. Scientific significance: The advancements made by project will be key in the reconstruction of the Tree of Life, both locally and globally. The resolution of sunflowers completes one lineage on the Tree of Life, while these new methods and markers will focus more widely on the accurate construction of the tree. Although the markers being collected will be used specifically for methods under this project, the capability for their use in other flowering plants will be of tremendous benefit. Additionally, the computational efforts used in this research have resulted in a new collaboration between computer scientists and biologists that has greatly enhanced the creativity of future research questions. An immediate educational impact has also been felt: at present, five undergraduates have been trained in valuable molecular techniques that can be applied in their future research.