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

纵观陆地植物的进化史，来自远亲谱系的陆生植物曾多次入侵水生环境。为了在这些完全不同的物理条件下生存，这些植物被选中来改变它们的营养、繁殖和传播系统。很少有活着的蕨类植物是水生的；大多数是陆生的和同孔的(带有单一的孢子类型)。异孢蕨类、半水生马尾蕨科和水生紫花蕨科是例外，它们属于一个进化谱系。现存的五个异孔蕨类植物属的研究很少，但其观赏孢子的化石记录对这些蕨类植物来说是相对较好的，显示出随着开花植物的崛起而出现的白垩纪多样性。在杜克大学的蕨类专家凯瑟琳·普莱尔和哈拉尔德·施奈德以及俄克拉荷马大学的古植物学家理查德·卢皮亚的合作下，研究人员将整合对所有已知水生蕨类物种进化速度和序列的形态和分子研究，以了解对水环境的适应历史。通过DNA序列比较，结合形态研究，将构建所有物种的全面系统发育图。用电子显微镜研究孢子的超微结构特征，研究孢子壁结构和纹饰的发育特征，以解释和整合该群的化石孢子。根据化石记录中出现的相对顺序，已经提出了许多形态趋势，为该组构建的明确的系统发育将使这些关于水生蕨类特征进化的想法得到检验。研究人员从形态学、DNA序列分析、系统发育方法、古植物学和定量分析等领域为这项研究带来了互补的技能。这项研究为检验从白垩纪到现代的现代蕨类植物区系的适应性辐射、水生生境的定居和发育变化的遗传模式的假说提供了一个理想的机会。

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.