Ecological Roles of Fungal Endophytes
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Endophytic fungi live within tissues of plant hosts without causing symptoms of disease. These fungi are broadly split into the taxonomically and ecologically cohesive Clavicipitaceous endophytes, which infect grasses, and the taxonomically diverse non-Clavicipitaceous endophytes, which are found in nearly all plants and have diverse ecological strategies. My dissertation has two sections: Section A investigates the intersection of Clavicipitaceous endophyte ecology with other ecological theory, including invasion ecology (Chapter II) and community ecology and climate change (Chapter III); Section B investigates the ecology of one group of non-Clavicipitaceous endophytes, the Xylariaceae, using a culture-based study in Ecuador (Chapter IV) and a next-generation sequencing based endophyte survey in Taiwan (Chapter V). Section B is centered on testing the Foraging Ascomycete (FA) hypothesis—the idea that some decomposer fungi may adapt an endophytic lifestyle to escape limitations in primary substrate in both time and space. In Chapter II, I utilized a host-specific Epichloë endophyte present ubiquitously in the European native range of the Pacific Northwest (PNW) invasive grass Brachypodium sylvaticum to test theories of invasion. In Chapter III, I examined the grass Agrostis capillaris in the context of a climate manipulation experiment in prairies in the PNW to elucidate patterns of interaction between multiple symbionts (Epichloë endophytes, dark septate root endophytes, and arbuscular mycorrhizal fungi) within single hosts across climatic variation. In Chapter IV, I began to test the FA hypothesis by examining spatial relationships of Xylaria endophytic fungi in the forest canopy with Xylaria decomposer fungi on the forest floor in a remote Ecuadorian cloud forest. In Chapter V, I build on the results from the previous study, using a novel technique to examine spatial ecology of the Xylariaceae, pairing traditional mycological collection with the preparation of a next-generation sequencing metabarcode library of endophytes over a much greater area. This dissertation includes previously published and unpublished coauthored material.