Phylogenetic Study of Homosporous Ferns Based on Chloroplast and Nuclear Gene Sequences and Morphology

9307068在确定同种孢子蕨类的自然进化谱系和将这些谱系划分为属和科方面的困难通常归因于收敛和平行进化对传统上用于蕨类分类的形态特征的影响。在很大程度上适应半沙漠条件或其他季节性干燥栖息地的钩毛状蕨类植物就是最好的例子。来自叶绿体基因组的分子数据不受作用于形态的与生境相关的选择性作用力的影响，并开始产生对蕨类植物进化和系统发育的基本见解。然而，最近对开花植物的研究发现，杂交、渐渗或谱系分类可能导致仅基于细胞质遗传的叶绿体基因组进行系统发育重建的重大错误。这引起了人们对蕨类植物的关注，因为异源多倍体杂交的高发生率和蕨类植物的高基本染色体数表明，现代蕨类植物可能是古老的多倍体，其祖先的网状进化一直是重要的。Gastony博士的项目将利用叶绿体DNA的分支分析分子数据(红细胞L基因的核苷酸序列)作为同种孢子蕨类的模型研究，以提供对唇状蕨类植物亲缘关系和系统发育的基本新见解。同样重要的是，该项目将使用来自核基因组(核糖体DNA的核苷酸序列)的分子数据来与叶绿体DNA的结果和传统的形态特征进行比较。综合的形态和分子数据将在全球范围内构成修改后的唇状蕨类植物分类及其系统发育关系重建的基础。

9307068 Gastony Difficulties in identifying natural evolutionary lineages in homosporous ferns and in circumscribing these lineages as genera and families are often attributed to the effects of convergent and parallel evolution on the morphological characters traditionally used in fern taxonomy. The cheilanthoid ferns, largely adapted to semi desert conditions or to other seasonally dry habitats, are the foremost examples of this. Molecular data from the chloroplast genome are unaffected by habitat related selective forces acting on morphology and are beginning to yield fundamental insights into fern evolution and phylogeny. However, recent studies on flowering plants have found some instances in which hybridization, introgression, or lineage sorting may lead to significant error in phylogenetic reconstructions based solely on the cytoplasmically inherited chloroplast genome. This raises concern for ferns because the high incidence of allopolyploid hybrids and high basic chromosome numbers in ferns suggest that modern ferns may be paleopolyploids in whose ancestry reticulate evolution has been important. Dr. Gastony's project will serve as a model study for homosporous ferns by using cladistically analyzed molecular data from chloroplast DNA (nucleotide sequences of the rbc L gene) to provide fundamental new insights into cheilanthoid fern relationships and phylogeny. Importantly also, the project will use molecular data f rom the nuclear genome (nucleotide sequences of ribosomal DNA) to compare with chloroplast DNA results and with traditional morphological characters. %%% The combined morphological and molecular data will form the basis of a revised classification of cheilanthoid ferns and of a robust reconstruction of their phylogenetic relationships, on a worldwide basis.