College of Agriculture & Natural Resources

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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

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Subject: search.filters.subject.Nectria

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    Pseudocospeciation of the mycoparasite Cosmospora with their fungal hosts
    (John Wiley & Sons Ltd., 2016-01-03) Herrera, Cesar S.; Hirooka, Yuuri; Chaverri, Priscila
    Species of Cosmospora are parasites of other fungi (mycoparasites), including species belonging to the Xylariales. Based on prior taxonomic work, these fungi were determined to be highly host specific. We suspected that the association of Cosmospora and their hosts could not be a result of random chance, and tested the cospeciation of Cosmospora and the their hosts with contemporary methods (e.g., ParaFit, PACo, and Jane). The cophylogeny of Cosmospora and their hosts was found to be congruent, but only host-parasite links in more recent evolutionary lineages of the host were determined as coevolutionary. Reconciliation reconstructions determined at least five host-switch events early in the evolution of Cosmospora. Additionally, the rates of evolution between Cosmospora and their hosts were unequal. This pattern is more likely to be explained by pseudocospeciation (i.e., host switches followed by cospeciation), which also produces congruent cophylogenies.
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    SYSTEMATICS OF THE GENUS COSMOSPORA (NECTRIACEAE, HYPOCREALES), AND COSPECIATION OF COSMOSPORA SPECIES WITH THEIR ASSOCIATED FUNGAL HOSTS.
    (2014) Herrera, Cesar Samuel; Chaverri, Priscila; Plant Science and Landscape Architecture (PSLA); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Cosmospora (in the broad sense; Nectriaceae, Hypocreales, Ascomycota) are fungi that parasitize other fungi, particularly fungi in the Xylariales (Ascomycota), or scale insects. Morphologically, these fungi are known for having one of the most simplest and smallest sexual fruiting bodies (<300 μm) among the Nectriaceae. The sexual spores are generally warted. The majority of Cosmospora species have acremonium-like or fusarium-like asexual states. The name Cosmospora is derived from the ornamentation in the sexual spores (Gr. cosmos = ornamented + Gr. spora = spore). The main goals of this dissertation were to revise Cosmospora sensu stricto, and to determine the evolutionary relationship between Cosmospora species and their associated fungal hosts. Additionally, Corallomycetella (Nectriaceae, Hypocreales, Ascomycota), a lineage basal to Cosmospora sensu lato, was revised as well. Molecular and classical taxonomic tools were used to revise the genera. A genus was recognized if the clade met the following criteria: 1) the clade was well supported, 2) the clade was associated with a unique asexual state, and 3) the clade was ecologically different. A species was recognized if the clade met the following criteria: 1) the clade was well supported in the majority of single gene trees, 2) the clade was morphologically different, and/or 3) the clade was ecologically different in regards to host. Cosmospora species were observed to be highly host specific. Thus, host was recognized as an important character to delineate species, and the host specificity led us to hypothesize that Cosmospora species and their associated hosts were cospeciation (i.e., their association was not random). Two new genera, nine new combinations, and eleven new species were described in the taxonomic work included in this dissertation. A significant global congruence was determined between the Cosmospora and host phylogenies. However, host-switch events seemed more abundant in the early lineages of the host, while cospeciation events seemed more common in more recent lineages of the host. This phylogenetic signature is consistent with pseudocospeciation, but it could not be confirmed given that divergence estimates could not be estimated.