DISSERTATION RESEARCH: Molecular Systematics and Evolution in Castilleja and Subtribe Castillejinae (Orobanchaceae).

University Of Washington, Seattle WA

Investigators

Abstract

Understanding the role that hybridization plays in creating plant species, and its impact on understanding evolutionary relationships is of vital importance to understanding the origins of biodiversity. Hybridization, or the interbreeding of different species, often creates a pattern in which the hybrid species displays characteristics intermediate to the two parent species. If hybridization is common within a species group, it can be difficult to distinguish species due to overlap in many of their distinguishing characteristics. Complicating matters, species of recent origin can be difficult to distinguish, because of a similar pattern of overlapping characters. To determine the importance of these different historical processes that result in similar patterns, first requires the reconstruction of patterns of genetic relationship between species (the 'family tree'). The large genus Castilleja (Indian Paintbrush), which is made up of ~180 species distributed chiefly in western North America, is an appropriate model to address these questions. Preliminary results indicate that the Castilleja, in which the majority of the species are perennial, has evolved from a group of closely related annual species. This contradicts the commonly held wisdom that annual plants evolve from perennial ancestors. However, a small radiation of annual paintbrush species in South America has been identified, but little study has been devoted to these plants, and their relationship to other Castilleja species is unknown. Thus, the goals of this research are 3-fold: 1) develop a well-supported, species-level evolutionary tree depicting the relationships among species of Castilleja, 2) determine the importance of a recent species radiation versus hybridization in creating the observed pattern of overlapping characteristics within Castilleja, and 3) investigate the relationship of the South American annual Castilleja species with respect to the remainder of the genus. These objectives will be accomplished by first sampling ~120 Castilleja species from their native ranges, and then comparing several DNA sequences between the sampled species. Using computer algorithms to compare the DNA sequences and extrapolate the evolutionary history of the group, it is possible to test the significance of the evolutionary processes that may have been instrumental to speciation in Castilleja. Results obtained will contribute not only to the understanding of patterns of diversification in species-rich groups, but also towards an understanding of some major processes involved in plant speciation. Completed and ongoing research will be reported at annual scientific meetings of the Botanical Society of America, American Society of Plant Taxonomists, and the Society for Systematic Biology. A website on Castilleja taxonomy and biology will be developed for the greater botanical and scientific community, as well as for the ongoing Tree of Life project. Results from the proposed research will be submitted to scientific journals for publication, and the results of this research will be incorporated into the upcoming treatment of Castilleja for the Flora of North America.