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

在白垩纪，开花植物迅速多样化，并迅速成为地球上植物的主导群体。它们的崛起迫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。蕨类植物非但没有被边缘化或灭绝，反而在森林下层和新出现的树冠层中茁壮成长并多样化。蕨类植物和石松植物在陆地植物中是独特的，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），它们都必须适应开花植物兴起所带来的新环境条件。许多热带附生蕨类配子体进化出比陆生蕨类配子体更多的叶子，这使它们能够活得更长，并且在不产生孢子的情况下繁殖。在竞争激烈的树冠环境中，这些是非常有益的特征，实际上可能使蕨类植物在这些栖息地中迅速多样化。配子体独立性的增加意味着蕨类植物在条件不利的情况下可以推迟孢子体的产生。因此，在一些附生物种中，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。这些具有长寿配子体的蕨类植物中有几种生长在夏威夷，那里的蕨类植物仍未得到充分研究。该项目将调查夏威夷这些蕨类植物的生态学，特别是有利于独立配子体种群进化的环境条件。为了了解控制孢子体和配子体生产的生态动力学，温度、光照水平和降水都将被测量。来自佛罗里达大学和夏威夷大学马诺阿分校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。研究结果将通过科普文章广泛传播。本研究将在夏威夷Koolau和Waianae山脉的5个站点分别以200、400、800和1000 m的间隔调查孢子体和独立配子体的植物区系。在每个地点，研究人员将在小路旁的10 × 10平方米的地块上收集附生孢子体，测量叶子的大小，并保存组织用于植物标本室收集和DNA提取。温度和光照水平将使用HOBO数据记录仪进行测量，降水将使用标准的倾卸桶雨量计进行记录。环境状况将在一年的时间内进行测量。这项研究的结果将使研究人员能够确定是什么条件阻止了蕨类植物孢子体的产生，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.