Phylogeny, Phylogeography, and Genetic Differentiation in California Calochortus (Liliaceae)

Calochortus植物属（百合科，约60种）在加利福尼亚有一个多样性的中心，在花的形式和栖息地上经历了惊人的多样化。一些物种局限于小区域，25%发生在蛇形土壤上。叶绿体DNA的突变差异分析表明，Calochortus由7个地理上紧密结合的类群组成，密切相关的物种往往具有毗邻的范围。三种主要的花型（例如“猫耳花”、“星形郁金香”）每种都出现了两到六次，蛇形植物的耐受性至少进化了七次。假设这种地理内聚和平行辐射是基因流动受限的产物，在小空间尺度上促进了遗传分化和物种形成；不同的谱系在独立入侵不同地区时可能进化出相似的适应性。为了验证这些想法，Givnish教授和他的学生将分析旧金山湾区的Calochortus物种之间的关系以及它们所占据的地形，使用核DNA变异，研究早期交配障碍作为地理和遗传距离的函数，重建过去的迁移模式，杂交，物种内部和物种之间的基因流动。他们的目标是：(1)重建湾区Calochortus的地理分化历史，并确定局限于蛇形的物种是彼此的近亲，还是从一个或多个广泛的物种独立衍生而来；(2)研究杂交和基因渗入在这个复杂群体中的作用；(3)分析围绕加州中央谷地的“环形物种”复合体内的遗传分化模式，以确定不断扩大和逐渐分化的种群最终相互毗邻的缝合带（突变遗传分化区域）。该研究将通过量化物种内部遗传分化和早期交配障碍的空间尺度，并将其与物种间分化的地理和形态模式联系起来，从而弥合分类学、系统学、群体遗传学和历史生物地理学的传统关注。研究结果将为加利福尼亚其他动植物类群的比较分析提供基础，包括正在进行的对几组植物和两栖动物的研究，以及涉及加利福尼亚山谷橡树的环形物种复群。遗传变异和分化模式的数据将对保护有价值。本项目将培养两名女性博士研究生，方向为分子系统发育学、系统地理学、群体遗传学和植物系统学。吉文尼斯教授将从代表性不足的少数族裔中招募两名本科生，协助数据收集和撰写高级论文。我们将建立一个关于卡罗科鸟进化的网站，为业余博物学家、自然资源保护主义者、专业植物学家和进化生物学家等广大读者提供研究结果和新的见解。

The plant genus Calochortus (Liliaceae family, with ca 60 species) has a center of diversity in California and has undergone striking diversification in flower form and habitat. Several species are restricted to small areas, and 25% occur on serpentine soils. An analysis of mutational differences in chloroplast DNA indicates that Calochortus is composed of seven geographically cohesive groups, with closely related species often having adjoining ranges. Three of the major floral forms ("cat's ears," "star tulips," for example) have arisen two to six times each, and serpentine tolerance has evolved at least seven times. It is hypothesized that such geographic cohesion and parallel radiations are the products of restricted gene flow, which should promote genetic differentiation and speciation at small spatial scales; different lineages may evolve similar adaptations as they invade different areas independently. To test these ideas, Prof. Givnish and his students will analyze the relationship of Calochortus species in the San Francisco Bay Area to each other and to landforms they occupy, using nuclear DNA variation, studies of incipient mating barriers as a function of geographic and genetic distance, and reconstruction of past patterns of migration, hybridization, and gene flow within and among species. Their objectives are to (1) reconstruct the history of geographic differentiation within the Bay Area Calochortus and determine whether the species restricted to serpentine are each other's closest relatives or have instead been derived independently from one or more of the wide-ranging species; (2) examine the role of hybridization and introgression in this complex group; and (3) analyze the pattern of genetic differentiation within a "ring-species" complex that surrounds California's Central Valley, to identify suture zones (areas of abrupt genetic differentiation) where expanding and gradually differentiating populations finally abutted each other.The proposed research will bridge traditional concerns of taxonomy, systematics, population genetics, and historical biogeography by quantifying the spatial scales at which genetic differentiation and incipient mating barriers arise within species, and relating these to the geographic and morphological patterns of divergence among species. Findings will provide the basis for comparative analyses involving other plant and animal groups in California, including ongoing research on several groups of plants and amphibians, and a ring-species complex involving the California valley oak. Data on patterns of genetic variation and differentiation will be of value to conservation. This project will train two female Ph.D. students in molecular phylogenetics, phylogeography, population genetics, and plant systematics. Prof. Givnish will recruit two undergraduates from underrepresented minorities to assist in data collection and develop senior theses. A web site on Calochortus evolution will be developed to bring results and new insights to a broad audience of amateur naturalists, conservationists, and professional botanists and evolutionary biologists.