Dissertation Research: Systematics of Spigelia (Loganiaceae): Tropical/Temperate Relationships and the Origin of a Temperate Disjunction

研究生Katherine Gould在德克萨斯大学的导师Billie Turner和Robert Jansen的指导下，正在研究美国loganaceae科的Spigelia属植物，该植物估计有50种，分布在北美洲、中美洲和南美洲。正在从植物标本馆收集的标本和从墨西哥和其他地方的实地考察中提取样本，以便为核DNA变异和叶绿体DNA限制酶变异的深入形态学研究和分子分析提供材料。目标是评估形态学特征，这些特征将为区分属中的物种提供可靠的特征，并通过两个分子数据集推断属内各部分的系统发育，测试它们之间的一致性并将它们整合到组合dna数据库中。一个主要的测试将集中在美国的三个本地物种上，并评估它们是组成一个单一的进化单位（一个分支）还是代表北温带的不同物种。一项辅助测试将评估位于密西西比河两侧、德克萨斯州和佛罗里达州的钉螺之间的关系。现代植物分类研究结合了形态学研究和较新的分子分析。形态学研究评估种群内和种群间营养和生殖性状的变化，以便为鉴定和评估物种状态指定可靠的特征。分子（DNA）数据可以测量物种之间的突变差异，并推断它们之间的系统发育（谱系）关系。以这种系统发育为指导，可以分析物种的地理分布，以检测随时间的迁移路径，并确定是否发生过单次或多次入侵。＊＊＊

9623495 Turner Graduate student Katherine Gould, with direction from advisers Billie Turner and Robert Jansen at University of Texas, is studying the American plant genus Spigelia of the Loganiaceae family, which has an estimated 50 species distributed in North, Central, and South America. Samples are being drawn from herbarium collections and from field expeditions in Mexico and elsewhere, to provide materials for both intensive morphological studies and for molecular analyses of nuclear DNA variation and chloroplast DNA restriction-enzyme variation. The goals are to assess morphological features that will provide reliable characters for distinguishing the species in the genus, and to infer a phylogeny of sections within the genus with the two molecular data sets, testing for concordance between them and integrating them in a combined-DNA database. One major test will focus on the three native species in the U.S. and assess whether these comprise a single evolutionary unit (a clade) or represent separate speciations into the north temperate zone. A subsidiary test will assess relationships between spigelias on opposite sides of the Mississippi River, in Texas and in Florida. %%% Modern taxonomic studies of plants combine morphological studies with newer molecular analyses. The morphological studies evaluate variation in vegetative and reproductive characters within and among populations in order to designate reliable features for identification and assess species status. Molecular (DNA) data allow measurement of mutational differences between species and the inference of phylogenetic (genealogical) relationships among them. With this phylogeny as guide, the geographical distributions of the species can be analyzed to detect migration pathways through time, and to determine whether single or multiple invasions have occurred. ***