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

9310979菲尔布里克和弗里奇洲际植物分离是检验地质历史变化模式的理想系统。开花植物Styrax属提供了一个这样的系统，在加利福尼亚州和地中海地区发现了几个种类的Imbricatae。这一类群加上其他21个具有类似分布模式的活植物类群，被认为是基于形态相似性的“Madrean-Tethyan”联系：即曾广泛存在的、从北美西南部横跨大西洋延伸到早第三纪中亚的干旱生境适应植被带的遗迹。关于这些洲际拆分存在的其他假说声称没有马德里安-特提斯走廊的证据，并坚持认为大西洋两侧的类群只是表面上看起来密切相关，但实际上是从跨越白令或北大西洋大陆桥迁徙的中古祖先独立派生出来的。研究生弗里奇在菲尔布里克博士的指导下进行的这项工作的目标是，通过从形态、DNA和蛋白质数据中产生独立的证据线，使用Styrax作为代表性群体来测试Madrean-Tethyan连续性假说。同工酶和叶绿体DNA变异产生的%%-%%遗传距离度量将估计分类单元的分化时间，而利用形态、叶绿体DNA和核核糖体DNA特征重建的系统发育将检验该类群的单系地位。对数据的分析将提供信息，表明哪种Madrean-Tethyan历史模型可能是正确的，并为继续进行分类学和进化研究提供这些植物的合理分类。***

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. ***