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

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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.