| This dissertation focusses on aspects of the biology of a diverse, microscopic, and challenging lineage of the Ascomycota, the Laboulbeniomycetes. These fungi utilize living arthropods for nutrition and for dispersal, have reduced hyphal systems, and have proved intractable to culture. Here we present the first detailed investigations of the class using molecular methods, specifically 18S and ITS rDNA sequences, which combined with morphological and ecological studies, have enabled us to probe some of the enduring questions regarding the biology of these fungi. A general introduction is followed by two studies on the phenomenon of 'position specificity' that provide compelling evidence for the recognition of alternate phenotypes. In one of our systems (Chitonomyces) precise positions of each phenotype are maintained through mating behaviors of the host beetles.;The remaining chapters explore the results of a first molecular-based phylogeny for the group. The genus Herpomyces, on cockroaches, is the earliest-diverging taxon. Surprisingly, we report evidence of asexual taxa (Chantransiopsis and Tetrameronycha) as sister to the remainder of the Laboulbeniales (excluding Herpomyces). Antheridial characters, features on which the earliest classifications were based, are shown to be homoplastic. On the other hand, features of perithecial development show an overall trend towards reduction, and appear to by phylogenetically informative. Relationships among the so-called 'aquatic genera' are poorly resolved in our analyses. The remainder of the taxa are divided into two major groupings and morphological characters are identified that support their split. Subclades are discussed further in light of information on thallus morphology, development, and host relationships. We present overall conclusions arising from this research and some suggestion for future research directions. Key Words: Ascomycota, Chantransiopsis, Chitonomyces, Hesperomyces, Laboulbeniales, Laboulbeniomycetes, molecular systematics, position specificity, Pyxidiophorales, Tetrameronycha. |
