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A different shade of hypha : cytological and molecular phylogenetic evidence for the independent rise of the hyphal habit in the class Monoblepharidomycetes (Chytridiomycota) Dee, Jaclyn Marie


Once the ancestors of fungi stopped moving and instead started reaching out with hyphae, their filamentous growth made possible new variety in form and habitat. Hyphae mediated substrate colonization, absorptive nutrition, mating and reproduction. Although shared across most familiar terrestrial fungal lineages, little was known about where hyphae evolved in early fungi. In chapter one, I review the phylogenetic origins of hyphae and current understanding of the cytology of hyphal tips. Better understanding of fungal phylogeny and hyphal growth near the base of the fungal tree was needed. In Chapter 2, I investigated the phylogeny and cytology in the Class Monoblepharidomycetes (Chytridiomycota), a group of deeply diverging, zoosporic fungi, encompassing a range of body types. Species can be either crescent or rod-shaped unicells or sprawling hyphal growths. I inferred a phylogeny of the fungi based on 28S ribosomal DNA sequence data using maximum likelihood (ML) and Bayesian inference methods. I recovered the monophyly of modern fungal phyla and the topology was comparable to the most taxonomically diverse and gene–rich phylogeny of the fungi to date. I used likelihood methods to trace the origins of hyphae on my likelihood tree, concluding that hyphae arose independently in the Monoblepharidomycetes and at least three other times in the fungi. Next, I searched for evidence of convergent evolution in the cellular organization of hyphal Monoblepharidomycetes using fluorescence and transmission electron microscopy. I showed that the hyphae of Monoblepharidomycetes have a novel form with an unusual microtubule cytoskeleton and without a typical fungal Spitzenkörper. This constitutes the first report on the cytology of hyphae from the Chytridiomycota. In Chapter 3, I discuss the significance of my research and possible future directions including cytological experiments on the Monoblepharidomycetes cytoskeleton.

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