Dissertation Research: Two Modes of Speciation in Coreopsis (Asteraceae): A Chloroplast DNA Study

在Coreopsis组中，Coreopsis(菊科)的物种形成既有渐变模式，也有盐生模式。来自这两组不同分类群的叶绿体DNA将被10种限制性内切酶消化，相应的过滤器将用8个克隆的叶绿体DNA片段进行探测。在三个逐渐分化的大花锦鸡儿二倍体形态变种中发现的多样性将被用来确定分类变种之间或其范围的两个主要、不连续的地理部分之间是否存在分歧。将对涉及紫锥菊及其衍生物的盐生物种形成事件进行审查，以确定物种内叶绿体DNA多样性的相对量是否与盐化事件相对应，如果是，那么伴随的种群瓶颈可能有多严重。对cpDNA多样性的初步调查揭示了相当大的种间、种群间和种群内的变异。这项研究的结果将对两种物种形成模式所涉及的遗传过程提供重要的见解，并将证明cpDNA在物种水平以下的多样性分析中的有效性。

Within Coreopsis section Coreopsis (Asteraceae) both gradual and saltational modes of speciation are represented. Chloroplast DNA from both sets of diverging taxa will be digested with ten restriction enzymes, and the corresponding filters will be probed with eight cloned chloroplast DNA fragments. The diversity found within the three gradually diverging diploid morphological varieties of C. grandiflora will be used to determine whether divergence is occurring between the taxonomic varieties or between the two major, discontinuous geographical portions of its range. The presumed saltational speciation event involving C. nuecensoides and its derivative C. nuecensis will be examined to determine whether the relative amounts of chloroplast DNA diversity within the species correspond with a saltational event, and if so, how severe the accompanying population bottleneck may have been. A preliminary survey of cpDNA diversity has revealed considerable interspecific, interpopulational, and intrapopulational variation. The results of this study will give important insights into the genetic processes involved in two modes of speciation, and will demonstrate the usefulness of cpDNA for diversity analyses below the species level.