Dissertation Research: Speciation Processes in Serpentine Endemics: A Molecular Systematic Study of the Streptanthus glanduloses Complex (Cruciferae)

稀有和特有物种为研究物种形成的原理和过程提供了独特的机会。腺链虫（十字花科）是一群特有的蛇形植物，其中大多数是稀有或濒危的。这个复合体代表了基质在种群和分类群分化中所起作用的一个特别显著的例子。这些一年生植物发生在加利福尼亚海岸山脉从特哈马县到圣路易斯奥比斯波县的蛇形土壤中，在不适合的非蛇形栖息地的干预区域中被隔离。这种隔离，伴随着近亲繁殖，可能导致在每个物种的种群中可以识别出许多不同的表型。该组的系统发育未知，分类划分有争议：从一个物种的三个变种到13个不同的物种已被确认。因此，S. glandullosus复合体不仅需要系统的研究，而且还提供了一个研究蛇形动物特有物种形成过程的良好论坛。Kruckeberg（1957）在种群间杂交实验的基础上表明，群体间的互育性与群体间的分离距离呈负相关。我们建议在克鲁克伯格经典的距离分离研究的基础上，结合酶电泳和叶绿体DNA的限制性内切位点分析来研究遗传差异、系统关系和进化过程。具体目标是：(1)评估人群之间的等位酶和cpDNA差异，并将遗传差异与地理模式联系起来；(2)利用cpDNA限制性位点数据构建该复合体的系统发育，并利用系统发育来评估古特有和新特有的推定例子，从更广泛的分类群中衍生出的限制分类群，以及蛇形耐受性的反复适应；(3)利用同酶数据估计种群间基因流动水平；(4)比较限制和广泛类群的等位酶变异水平。对腺芽孢杆菌复合体的互育、同酶和限制性位点的综合分析为研究物种形成过程提供了一个几乎无与伦比的平台，并将为复合体的健全管理提供必要的信息。

Rare and endemic species provide unique opportunities to study the principles and processes of speciation. The Streptanthus glandulosus complex (Cruciferae) is a group of serpentine endemics, most of which are rare or threatened. This complex represents a particularly striking example of the role of substrate in the divergence of populations and taxa. These annual plants occur on serpentine soils in disjunct populations in the Coast Ranges of California from Tehama County to San Luis Obispo County, isolated by intervening regions of unsuitable, non-serpentine habitat. this isolation, accompanied by inbreeding, may have resulted in the many different phenotypes identifiable among populations within each species. The phylogeny of the group is unknown and taxonomic delimitations are disputed: from three varieties of one species to 13 distinct species have been recognized. Thus, the S. glandulosus complex not only requires systematic study but it also offers an excellent forum in which to study speciation processes in serpentine endemics. Based on interpopulational crossing experiments, Kruckeberg (1957) showed a negative correlation between interfertility of populations of the complex and the distance by which they were separated. We propose to build on Kruckeberg's classic studies of isolation by distance using a combination of enzyme electrophoresis and restriction site analysis of chloroplast DNA to examine genetic divergence, systematic relationships, and evolutionary processes. The specific objectives are : (1) assess allozymic and cpDNA divergence among populations and correlate genetic divergence with geographic patterns; (2) construct a phylogeny of the complex using cpDNA restriction site data and use the phylogeny to evaluate putative examples of paleoendemism and neoendemism, recent derivation of restricted taxa from more widespread ones, and recurrent adaptation of serpentine tolerance; (3) estimate levels of interpopulational gene flow using allozymic data; and (4) compare levels of allozyme variability in restricted and widespread taxa. The integration of interfertility, allozymic, and restriction site analyses of the S. glandulosus complex offers an almost unparalleled venus from which to study speciation processes, and will provide the information necessary for sound management of the complex.