DISSERTATION RESEARCH: The Evolutionary Significance of Gametophyte Morphology in Epiphytic Ferns

在白垩纪，开花植物迅速多样化，并迅速成为地球上的主要植物群。它们的崛起使其他几种植物谱系灭绝或严重减少了它们的多样性。蕨类植物是这种模式的唯一例外。蕨类植物并没有被边缘化或灭绝，而是在森林的林下植被和新出现的树冠中蓬勃发展。蕨类植物和石松植物在陆地植物中是独一无二的，它们有两个独立的生命周期阶段（单倍体配子体和二倍体孢子体），这两个阶段都必须适应显花植物兴起所创造的新环境条件。许多热带的附生蕨类配子体进化出比陆地同类更多的叶子，这使它们能够活得更长，繁殖时不产生孢子。在竞争激烈的林冠环境中，这些都是非常有益的特征，实际上可能使蕨类植物在这些栖息地中迅速多样化。配子体的独立性增加意味着，如果条件不利，蕨类植物可以推迟孢子体的产生。因此，在几个附生物种中，我们观察到一种空间分离世代的模式，其中配子体可以在比孢子体更广泛的条件下生长。其中几种具有长寿配子体的蕨类植物生长在夏威夷，那里的蕨类植物仍然研究不足。这个项目将调查这些蕨类植物在夏威夷的生态，特别是有利于独立配子体种群进化的环境条件。温度，光照水平和降水量都将被测量，以了解控制孢子体和配子体生产的生态动力学。来自佛罗里达大学和位于马诺阿的夏威夷大学的一名研究生和几名本科生将接受不同领域和实验室方法的培训。这项研究将在夏威夷的库劳和威克斯堡山脉的五个站以200、400、800和1,000米的间隔调查孢子体和独立配子体植物区系。在每个地点，研究人员将收集位于小径外的10 × 10平方米的附生孢子体，测量叶片的大小，并保存组织用于标本馆收集和DNA提取。将使用Onset流浪汉数据记录仪测量温度和光照水平，并使用标准翻斗式雨量计记录降水量。环境条件将在一年内进行测量。这项研究的结果将使研究人员能够确定哪些条件会阻止蕨类植物产生孢子体，并为夏威夷群岛蕨类植物的多样性和进化提供新的见解。

During the Cretaceous, flowering plants diversified rapidly and quickly became the dominant group of plants on the planet. Their rise pushed several other plant lineages to extinction or severely reduced their diversity. Ferns are the only exception to this pattern. Rather than being marginalized or driven to extinction, ferns actually thrived and diversified in both the forest understory and the newly available canopy. Ferns and lycophytes are unique among land plants in having two independent stages of the life cycle (haploid gametophyte and diploid sporophyte), both of which had to adapt to the new environmental conditions created by the rise of flowering plants. Many tropical, epiphytic fern gametophytes evolved to produce more leaves than their terrestrial counterparts, which enable them to live longer and to reproduce without producing spores. These are highly beneficial traits in the competitive canopy environment that may actually have enabled ferns to diversify rapidly in these habitats. The increased independence of the gametophyte means that ferns can postpone the production of sporophytes if conditions are unfavorable. As a result, in several epiphytic species we observe a pattern of spatially separated generations, in which the gametophyte can grow in a much broader range of conditions than its sporophyte. Several of these fern species with long-lived gametophytes grow in Hawaii, where ferns remain understudied. This project will investigate the ecology of these ferns in Hawaii, particularly the environmental conditions that favor the evolution of independent gametophyte populations. Temperature, light levels, and precipitation will all be measured in order to understand the ecological dynamics that govern sporophyte and gametophyte production. One graduate student and several undergraduates from the University of Florida and University of Hawaii at Manoa will be trained in diverse field and laboratory methods. Results from the study will be broadly disseminated via popular science articles.This research will survey sporophyte and independent gametophyte floras at five stations in the Koolau and Waianae Mountain ranges of Hawaii at 200, 400, 800, and 1,000 m intervals. At each site, researchers will collect epiphytic sporophytes in 10 X 10 m square plots located off the trail, measure the size of fronds, and preserve tissue for herbarium collections and DNA extraction. Temperature and light levels will be measured using Onset HOBO data loggers, and precipitation will be recorded with standard tipping bucket rain gauges. Environmental conditions will be measured over the course of one year. The results of this study will allow researchers to determine what conditions prevent sporophyte production in ferns, and provide new insights into the diversity and evolution of ferns on the Hawaiian Islands.