Dissertation Research: Evolution and Systematics of a Widespread Polyploid Fern Complex, Dryopteris filix-mas

在德克萨斯理工大学Charles Werth教授的指导下，研究生Lilin Xiang正在研究所谓的雄性蕨类植物（Dryopteris filix-mas）在其广泛的北半球分布范围内的起源和多样化。作为一种多倍体植物，雄性蕨类植物被认为结合了来自两个或更多亲本二倍体蕨类物种的染色体，这些染色体杂交产生双染色体后代。怀疑二倍体亲本是欧亚大陆的毛蕨，但也将研究美洲和中国的分类群。一个目标是区分单一起源后的分散，或在分布范围内的多个起源，可能来自不同大陆的不同亲本物种。来自分子生物学的新证据将有助于解决这个问题，包括蛋白质变异的电泳分析（遗传变异的间接测量，主要取样核基因）和叶绿体基因的直接DNA测序。正在收集来自北美、欧洲、土耳其和中国的种群样本，以广泛覆盖这类蕨类植物已知的形态多样性。多倍体，或多组染色体（有时能使不育的杂交植物恢复生育能力）在陆地植物中很普遍，尤其是蕨类植物。如在雄性蕨类，毛蕨，它经常与一个广泛的，几乎杂草的分布，伴随着微小的形态变化。多倍体是一次产生并广泛分布到现在的范围，还是通过在当前分布的各个部分重复杂交事件而产生的，这是一个仅用传统的形态学和解剖学分类特征难以回答的问题。来自同工酶分析和DNA测序的新分子证据，来自广泛的种群样本，包括几个假定的亲本分类群，将有助于解决这个问题。反过来，Dryopteris的案例将增加分析多倍体植物分类群历史生物地理学的严谨研究的数量。

9701318 Werth Graduate student Lilin Xiang, under the direction of Prof. Charles Werth at Texas Tech University, is studying the origin and diversification of the so-called male fern, Dryopteris filix-mas, over its wide northern-hemisphere distributional range. A polyploid plant, the male fern is thought to combine sets of chromosomes from two or possibly more parental diploid fern species that hybridized to produce doubled-chromosome offspring. Suspected diploid parents are Eurasian Dryopteris species, but American and Chinese taxa will also be studied. One goal is to distinguish between a single origin followed by dispersal, or multiple origins over the range of distribution, possibly from different parental species on the different continents. New evidence from molecular biology will help solve the problem, including electrophoretic analysis of protein variation (an indirect measure of genetic variability, sampling mostly nuclear genes) and direct DNA sequencing of a chloroplast gene. Population samples from North America, Europe, Turkey, and China are being gathered to provide extensive coverage of the morphological diversity known in this group of ferns. Polyploidy, or multiple sets of chromosomes (which sometimes restores fertility to otherwise sterile plant hybrids), is widespread in land plants, especially in ferns. As in the male fern, Dryopteris filix-mas, it is often associated with a widespread, almost weedy distribution, accompanied by minor morphological variation. Whether the polyploid arose once and dispersed widely to its present range, or arose through repeated hybridization events in various parts of the current distribution, is a question difficult to answer with only traditional taxonomic characters of morphology and anatomy. New molecular evidence from allozyme analyses and DNA sequencing, drawn from extensive population samples across the range and including several putative parent taxa, will help resolve the matter. In turn, the Dryopteris case will add to the small number of rigorous studies that analyze the historical biogeography of polyploid plant taxa.