Morphological and Ecological Diversification In the Homobasidiomycetes: A Molecular Phylogenetic Analysis

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9903835Hibbett and Donoghue Homobasidiomycetes include the mushroom-forming fungi and their relatives. About 13,500 species have been described, which is about 23% of all known species of fungi. The fruiting bodies of homobasidiomycetes include conspicuous, developmentally integrated structures such as mushrooms and puffballs, as well as very simple forms such as the crust-like fruiting bodies of "corticioid" fungi. Homobasidiomycetes play major roles in carbon cycling in terrestrial ecosystems; they comprise the majority of wood-decay fungi and ectomycorrhizal fungi (associated with tree roots); and they also include mycoparasites, insect symbionts, lichens, and litter decomposers. Although individual groups of these fungi have been studied intensively, their overall pattern of morphological and ecological evolution has not been determined because to date there has existed no broad well-supported phylogenetic framework for the group. Over the last few years, considerable progress has been made in understanding homobasidiomycete phylogeny through the use of new DNA sequence characters, particularly the genes encoding nuclear and mitochondrial ribosomal RNA (rDNA). This project will expand the database of nuclear and mitochondrial rDNA sequences and add new data from protein-coding genes under study, such as the tubulins or RNA polymerases. Taxon sampling will target problematic groups such as the polyporoid, hymenochaetoid, and cantharelloid groups of fungi, whose relationships remain weakly supported by the existing molecular data. Conventional protocols for phylogenetic analyses will be employed, and in addition the investigators will explore the use of "supertrees" for combining or collating independent phylogenetic trees with overlapping sets of taxa in order to construct a composite phylogenetic hypothesis. The trees will be used to construct phylogenetic classifications and to study historical patterns of evolution in selected morphological and ecological characters. Specific characters to be investigated include: corticioid versus erect fruiting bodies; brown rot versus white rot modes of wood decay; and ectomycorrhizal versus saprotrophic and pathogenic modes of nutrition. A broad framework phylogeny for the homobasidiomycetes will facilitate, for example by identifying sister groups and nearest outgroups, more intensive analyses of morphological and physiological changes in these fungi.