Dissertation Research: Phylogenetic Patterns and Molecular Divergence among Intercontinentally Disjunct Species of Styrax (Styracaceae)

[9310979] Philbrick和Fritsch洲际植物断裂是检验地质历史变化模型的理想系统。开花植物Styrax属提供了一个这样的系统，在加利福尼亚和地中海地区有几个叠毛蕨系列的物种。这一类群与其他21个现存的植物类群有着相似的分布模式，基于形态相似性，它们被认为是“马德林-特提斯”联系：第三纪早期从北美西南部横跨大西洋延伸到中亚的一个曾经广泛分布的适应栖息地的干旱植被带的遗迹。关于这些洲际断层存在的另一种假说认为，没有证据表明马德林-特提斯走廊的存在，并认为大西洋两岸的分类群只是表现出密切的联系，但实际上是独立于跨白令海峡或北大西洋陆桥迁移的mesic祖先。研究生Fritsch在Philbrick博士的指导下进行的这项工作的目的是通过从形态学、DNA和蛋白质数据中产生独立的证据线，以Styrax为代表群体，测试马德林-特提斯连续性假设。从Styrax种群内和种群间同工酶和叶绿体DNA变异产生的遗传距离测量将估计分类群分化时间，而利用形态学、叶绿体DNA和核糖体DNA特征对叠毛系进行系统发育重建将测试该群体的单系状态。对这些数据的分析将提供信息，表明马德兰-特提斯历史的哪个模型可能是正确的，并为这些植物的分类和进化研究提供一个健全的分类。＊＊＊

9310979 Philbrick and Fritsch Intercontinental plant disjunctions are ideal systems with which to examine models of geohistorical change. The flowering plant genus Styrax provides one such system, with several species of the Series Imbricatae occurring in California and in the Mediterranean region. This group plus 21 other living plant groups sharing a similar distributional pattern have been proposed as "Madrean-Tethyan" links based on morphological similarity: relicts of a once widespread dry habitat-adapted vegetation belt stretching from southwestern North America trans-Atlantically to central Asia in the early Tertiary. Alternative hypotheses for the existence of these intercontinental disjunctions claim no evidence for a Madrean-Tethyan corridor and maintain that taxa on either side of the Atlantic only appear closely related, but have actually been derived independently from mesic ancestors that migrated across either the Bering or the North Atlantic land bridges. The objective of the work by graduate student Fritsch under the direction of Dr. Philbrick is to test the Madrean-Tethyan continuity hypothesis using Styrax as a representative group by producing independent lines of evidence generated from morphological, DNA, and protein data. %%% Genetic distance measures generated from isozyme and chloroplast DNA variation within and among populations of Styrax will estimate taxon divergence times, whereas phylogenetic reconstruction of Series Imbricatae using morphological, chloroplast DNA, and nuclear ribosomal DNA characters will test the monophyletic status of the group. Analysis of the data will provide information indicating which model of Madrean-Tethyan history is likely to be correct as well as provide a sound classification of these plants for continuing taxonomic and evolutionary studies. ***