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

9701318 Werth研究生向丽琳在德克萨斯理工大学Charles Werth教授的指导下，研究了所谓的雄性蕨类--鳞毛蕨属在其广泛的北半球分布范围内的起源和多样性。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植物的染色体组，这些二倍体蕨类植物杂交产生了双染色体后代。可疑的二倍体父母是欧亚鳞毛虫物种，但美国和中国的分类群也将被研究。一个目标是区分单一来源然后扩散，或在分布范围内的多个来源，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，主要是对核基因进行采样)和叶绿体基因的直接DNA测序。来自北美、欧洲、土耳其和中国的种群样本正在被收集，以提供在这组蕨类植物中已知的形态多样性的广泛覆盖。多倍体，或多组染色体(有时会使原本不育的植物恢复生育能力)，在陆地植物中普遍存在，特别是在蕨类植物中。与雄性蕨类植物鳞毛蕨属一样，它通常与广泛的、几乎杂草的分布有关，并伴随着微小的形态变异。多倍体是一次性产生并广泛扩散到目前的范围，还是通过在当前分布的不同部分反复杂交而产生的，仅用传统的形态和解剖学特征很难回答这个问题。来自等位酶分析和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，将有助于解决这一问题。反过来，鳞毛蕨属的案例将增加分析多倍体植物分类群历史生物地理学的少数严格研究的基础上。

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.