Dissertation Research: The Evolution and Diversification of Bursera subgenus Bullockia (Burseraceae).

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Common Summary for non-specialists: (217 words)Biologists have claimed that hybridization between species is an important evolutionary phenomenon in plants, yet the vast majority of corroborating evidence derives from research using herbs growing in temperate climates. As a consequence, we do not know how accurately this assertion describes the evolutionary biology of tropical woody plants. To address the applicability of this idea to tropical plants, we will examine a group of tropical trees touted for its propensity to hybridize at the species and population level. The group, Bursera subgenus Bullockia (family Burseraceae), consists of over 40 species that range from Arizona to Bolivia. It is purported to include a handful of stabilized hybrid species and multiple, localized hybrid swarms. We will construct phylogenies or evolutionary hypotheses of relationships of the species using nuclear DNA sequences and chloroplast restriction site data to determine whether "hybrid" species indeed exist in this group. We will also genetically fingerprint a potential hybrid swarm of Bursera species located in the Galapagos to test for hybridity and to elucidate the geographic component of gene flow between species of these long-lived trees. The results of this study will contribute new information to our generalized understanding of hybridization in tropical, woody plants while they augment the systematic knowledge of Bursera and the exclusively tropical family of trees to which it belongs.Significance summary: (197 words)This project will examine a commonly held belief in plant evolutionary biology using a group of tropical trees. This assessment is significant because the premise that interspecific hybridization is a potent, relatively common evolutionary phenomenon is based primarily on information from temperate, herbaceous plants and need not necessarily apply to tropical woody plants, which have radically different life histories. We will increase our generalized understanding of the extent and evolutionary consequences of interspecific hybridization by testing purported stabilized hybrid species in a tropical, woody plant genus, Bursera (family Burseraceae). We will also improve our understanding of the formation of hybrid swarms and gene flow between tropical, woody plants by testing the isolated, geologically young populations of Galapagos Bursera for reported evidence of introgression. Additionally, the hypotheses of evolutionary relationships generated by this project will contribute new information to the systematics of Bursera and the Burseraceae, a family mostly unstudied at the molecular level. This project will help answer not only longstanding questions about the evolutionary history of this particular group such as whether stabilized hybrid Bursera species exist and whether Bursera can form interspecific hybrid swarms but also whether Bursera and Commiphora, its African relative, are congeneric.