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西南部和墨西哥的半荒漠或裸露条件，长期以来一直困扰着分类学家和生物学家，他们对这些植物的系统发育关系和进化过程感兴趣。为了解决这个问题，印第安纳大学的Gerald Gastony博士和George Yatski evych博士利用分子分析的新生物技术工具，研究了北美具有代表性的菊科蕨类植物属和种的叶绿体DNA遗传变异。因为DNA不像茎、叶和生殖结构那样受到环境影响的改变，所以比较物种之间的核苷酸差异可以揭示所研究物种的谱系亲缘关系。通过用在特定核苷酸位置裂解分子的酶(所谓的限制酶，从细菌发展而来)来消化叶绿体DNA，可以获得大量物种的比较数据。他们的初步数据显示了大量的限制酶位点变异性，表明物种之间存在广泛的突变差异。计算机程序将被用来分析数据，并根据物种共同的DNA特征将物种安排到最可能的进化群体中。这一系统发育将允许对这些蕨类植物在适应恶劣生境的进化中物种形成和特征趋同的过程进行详细的分析。

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.