Taxonomic and molecular systematic studies of the Harpellales (Trichomycetes) toward understanding the diversity, evolution and dispersal of gut fungi.

摘要

The class Trichomycetes, gut fungi, are unique, understudied, obligate symbionts of various Arthropoda. The number of taxa of gut fungi underestimates their actual diversity. The Harpellales, one of three fungal orders, was the focus of the dissertation. Harpellales, possessing asexual trichospores and sexual biconical zygospores, include the Harpellaceae and Legeriomycetaceae, and are unbranched or branched, respectively. It is the only order with culturable species, but most genera are unculturable. Previous molecular studies have included only culturable species. The goals of the dissertation were to (1) collect and identify taxa to study morphological characters of taxonomic importance; (2) develop molecular systematic approaches to infer the phylogeny using rDNA sequence data; and (3) use molecular methods to identify ovarian cyst stages. Surveys led to the discovery of new species of Harpellales: Furculomyces septentrionalis, Legerioides tumidus, Orphella avalonensis, Harpellomyces abruptus, and Stachylina litoralis. The publication of L. tumidus, a new genus from isopods, marked the first report of a harpellid from a non-insect host. Another new host order, Trichoptera, was identified from several locations in North America. All surveys yielded range extensions for known taxa. Cladistic analyses of rRNA gene sequences demonstrated that Orphella is not circumscribed within an otherwise monophyletic group of Harpellales. The molecular data do not support the current two family system of classification. The two largest genera, Smittium and Stachylina are not monophyletic and there is no evolutionary pattern among trichospore shape and size as well as zygospore type. The sequence data for ovarian cysts establish that this stage is part of the Harpellales life cycle and demonstrate their utility to identify species of gut fungi, either before or after germ tube production. The greatest accomplishment that this study may purport is that by utilizing the PCR techniques and methodological approaches developed herein, it was possible to generate sequence data from microscopic amounts of gut fungi dissected from and including mixed host gut contents. This should promote future studies with unculturable taxa of the Harpellales, not available for this investigation, and with other molecular markers, to infer the phylogeny of these gut endobionts.