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。腺链霉菌复合体(十字花科)是一组蛇形的特有种，大多数为稀有或受威胁。这种复合体是底物在种群和类群分化中所起作用的一个特别明显的例子。这些一年生植物生长在加利福尼亚州海岸山脉从Tehama县到San Luis Obispo县的分离种群的蛇形土壤上，被不适合的非蛇形栖息地的中间区域隔开。这种隔离，伴随着近亲交配，可能导致了在每个物种的种群中可以识别出许多不同的表型。该群的系统发育尚不清楚，分类界限也存在争议：从一种的三个变种到13个不同的种已被识别。因此，腺链霉菌复合体不仅需要系统的研究，而且它还提供了一个研究蛇纹石特有物种形成过程的极好的论坛。根据种群间杂交实验，Kruckeberg(1957)表明，复合体种群的干扰程度与它们之间的距离呈负相关。我们建议在Kruckeberg关于距离隔离的经典研究的基础上，使用叶绿体DNA的酶电泳法和限制性内切酶切点分析相结合的方法来研究遗传分化、系统关系和进化过程。具体目标是：(1)评估种群间的等位基因和cpDNA差异，并将遗传差异与地理模式相关联；(2)利用cpDNA限制性酶切位点数据构建复合体的系统发育树，并利用该系统发育树评估古特有和新特有的推定实例、从更广泛的受限分类群中新衍生的受限分类群以及蛇纹石耐性的反复适应；(3)利用等位酶数据估计种群间基因流动的水平；以及(4)比较限制性类群和广布类群的等位酶变异性水平。腺链球菌复合体的干扰性、等位酶和限制酶分析的集成为研究物种形成过程提供了一个几乎无与伦比的场所，并将为该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.