Reconstructing the evolution of agarics from nuclear gene sequences and basidiospore ultrastructure.

Traditional classifications of agaric fungi involve gross morphology of their fruit bodies and meiospore print-colour. However, the phylogeny of these fungi and the evolution of their morphological and ecological traits are poorly understood. Phylogenetic analyses have already demonstrated that characters used in traditional classifications of basidiomycetes may be heavily affected by homoplasy, and that non-gilled taxa evolved within the agarics several times. By integrating molecular phylogenetic analyses including domains D1-D3 and D7-D8 of nucLSU rDNA and domains A-C of the RPB1 gene with morphological and chemical data from representative species of 88 genera, we were able to resolve higher groups of agarics. We found that the species with thick-walled and pigmented basidiospores constitute a derived group, and hypothesize that this specific combination of characters represents an evolutionary advantage by increasing the tolerance of the basidiospores to dehydration and solar radiation and so opened up new ecological niches, e.g. the colonization of dung substrates by enabling basidiospores to survive gut passages through herbivores. Our results confirm the validity of basidiospore morphology as a phylogenetic marker in the agarics.