Phylogenetic Relationships in Cheilanthoid Ferns (Adiantaceae) Based on Chloroplast DNA Restriction Site Variation and rbcL Sequence Data

大量的蕨类植物适应了西南部和墨西哥的半沙漠或其他暴露环境，长期以来一直困扰着对这些植物的系统发育关系和进化过程感兴趣的分类学家和生物学家。利用分子分析的新生物技术工具，为了解决这一问题，美国印第安纳大学的Gerald Gastony和George Yatskievych正在研究北美菊科蕨类属和种的代表性样本叶绿体DNA的遗传变异。因为DNA不像茎、叶和生殖结构那样受环境影响的影响，所以物种间核苷酸差异的比较可以揭示所研究物种的宗谱亲缘关系。通过使用在特定核苷酸位点切割分子的酶（所谓的限制性位点酶，从细菌中发展而来）消化叶绿体DNA，可以获得大量物种的比较数据。他们的初步数据揭示了大量的限制性内切酶位点变异，表明物种之间存在广泛的突变差异。计算机程序将用于分析数据，并根据物种共有的DNA特征，将它们划分为最可能的进化组。这种系统发育将允许详细分析这些蕨类植物在适应恶劣栖息地的进化过程中的物种形成和特征趋同过程。

The large numbers of ferns adapted to semi-desert or otherwise exposed conditions in the Southwest and Mexico have long perplexed taxonomists and biologists interested in the phylogenetic relationships and processes of evolution in these plants. With new biotechnological tools of molecular analysis, Drs. Gerald Gastony and George Yatskievych of Indiana University are studying genetic variation in chloroplast DNA of representative samples of genera and species of Cheilanthoid ferns of North America, to solve this problem. Because DNA is not subject to modifying environmental influences in the way that stems, leaves, and reproductive structures are, the comparison of nucleotide differences among species can reveal genealogical affinities of the species examined. By digesting the chloroplast DNA with enzymes that cleave the molecule at specific nucleotide sites (so-called restriction-site enzymes, developed from bacteria) comparative data from a large number of species can be obtained. Their preliminary data reveal extensive amounts of restriction-enzyme site variability, indicating extensive mutational differences among species. Computer programs will be used to analyze the data and to arrange species into the most probable evolutionary groupings on the basis of their shared DNA characteristics. This phylogeny will then permit detailed analysis of processes of speciation and of character convergence in these ferns in their adaptive evolution to harsh habitats.