Collaborative Research: Using phylogeny to Investigate the History of Morphological Evolution in Heterosporous Ferns

在陆生植物的进化史上，来自远亲谱系的陆生植物不断入侵水生环境。为了在这些非常不同的物理条件下生存，这些植物被选择来改变它们的营养、繁殖和传播系统。很少有活着的蕨类植物是水生的；大多数是陆生和同孢子（具有单一孢子类型）。例外的是异孢子蕨类，半水生的Marsileaceae和水生的saliniaceae，它们属于单一的进化谱系。现存的五属异孢子蕨类植物很少被研究，但它们的装饰孢子的化石记录相对较好，表明白垩纪的多样化与开花植物的兴起同时代。杜克大学的蕨类植物专家Kathleen Pryer和Harald Schneider与俄克拉荷马大学的古植物学家Richard Lupia合作，研究人员将对所有已知的水生蕨类物种的进化速度和序列进行形态学和分子研究，以了解水生环境的适应历史。所有物种的全面系统发育将从DNA序列比较中构建，并结合形态学研究。利用电子显微镜研究孢子的超微结构特征，探讨孢子壁结构和纹饰的发育特征，以解释和整合该组已知的化石孢子。基于化石记录中出现的相对顺序，已经提出了许多形态趋势，为该群体构建的明确系统发育将允许测试这些关于水蕨类植物特征进化的观点。研究人员将形态学、DNA序列分析、系统发育方法、古植物学和定量分析等领域的互补技能带到研究中。这项研究提供了一个理想的机会来测试关于从白垩纪到最近的现代蕨类植物群的适应性辐射，水生栖息地的殖民化以及发育变化的遗传模型的假设。

Throughout the evolutionary history of land plants there have been repeated invasions of aquatic environments by terrestrial plants from distantly related lineages. In order to survive these very different physical conditions, these plants have been selected to modify their vegetative, reproductive, and dispersal systems. Few living ferns are aquatic; most are terrestrial and homosporous (bearing a single spore type). The exceptions are the heterosporous ferns, the semi-aquatic Marsileaceae and aquatic Salviniaceae, which belong to a single evolutionary lineage. The five extant genera of heterosporous ferns have been little studied, but the fossil record of their ornamented spores is relatively good for these ferns, showing a Cretaceous diversification contemporary with the rise of the flowering plants. In a collaboration between fern specialists Kathleen Pryer and Harald Schneider at Duke University and paleobotanist Richard Lupia at University of Oklahoma, the researchers will integrate morphological and molecular studies on the rates and sequences of evolution of all the known species of water ferns, to understand the history of adaptations to the aquatic environment. A comprehensive phylogeny of all the species will be constructed from DNA sequence comparisons, integrated with morphological studies. Spore ultrastructural characters will be studied with the electron microscope to investigate developmental features of spore wall construction and ornamentation, in order to interpret and integrate fossil spores known for the group. Numerous morphological trends have been proposed on the basis of the relative order of appearance in the fossil record, and the explicit phylogeny constructed for the group will allow testing of these ideas about character evolution in water ferns. The investigators bring complementary skills to the study from fields of morphology, DNA sequence analysis, phylogenetic methods, paleobotany, and quantitative analyses. The study provides an ideal opportunity to test hypotheses about the adaptive radiation of the modern fern flora from the Cretaceous to the Recent, the colonization of aquatic habitats, and genetic models of developmental change.