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

生物学家声称物种之间的杂交是植物进化中的一个重要现象，然而绝大多数确凿的证据来自对生长在温带气候的草药的研究。因此，我们不知道这种说法如何准确地描述了热带木本植物的进化生物学。为了说明这一观点对热带植物的适用性，我们将研究一组热带树木，因为它们在物种和种群水平上具有杂交倾向。该组，Bursera亚属Bullockia （Bursera科），由40多个物种组成，分布在亚利桑那州到玻利维亚。据称，它包括少数稳定的杂交物种和多个，局部杂交群体。我们将利用核DNA序列和叶绿体限制性位点数据构建物种关系的系统发育或进化假设，以确定该群体中是否确实存在“杂交”物种。我们还将对位于加拉帕戈斯群岛的Bursera物种的潜在杂交群体进行遗传指纹鉴定，以测试杂交性，并阐明这些长寿树木物种之间基因流动的地理成分。这项研究的结果将为我们对热带木本植物杂交的普遍理解提供新的信息，同时它们增加了对Bursera及其所属的热带树木家族的系统认识。这个项目将用一组热带树木来检验一个普遍持有的关于植物进化生物学的观点。这一评估意义重大，因为种间杂交是一种强有力的、相对普遍的进化现象的前提主要是基于温带草本植物的信息，而不一定适用于具有完全不同生活史的热带木本植物。我们将通过测试热带木本植物Bursera （Burseraceae家族）中所谓稳定的杂交物种，来增加我们对种间杂交程度和进化后果的广义理解。我们还将通过测试加拉帕戈斯Bursera孤立的、地质上年轻的种群来提高我们对杂交群体的形成和热带木本植物之间基因流动的理解，以寻找已报道的遗传渗透的证据。此外，本项目所产生的进化关系假说将为Bursera和Burseraceae这一尚未在分子水平上进行研究的科的系统学提供新的信息。这个项目不仅有助于回答关于这个特定群体的进化史的长期问题，比如是否存在稳定的杂交Bursera物种，Bursera是否可以形成种间杂交群体，以及Bursera和它的非洲近亲Commiphora是否同属。

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.