Abstract
The family Russulaceae is an iconic family of mushroom-forming
Basidiomycetes both because of its importance as an edible mushroom in many
parts of the world and its high species diversity in both temperate and tropical
forested biomes. While much mycological research has been focused on this
group, recent systematic and ecological research has failed to develop a
comprehensive or cohesive organization by which to understand the evolutionary
relationships, patterns of diversification, or functional importance of the group.
Recently, interest in ectomycorrhizal fungi (EmF), of which Russulaceae is a key
lineage, has greatly increased due to the recognition of the importance of EmF in
carbon sequestration in the face of global climate change. By specifically taking a
lineage-based approach to the study of Russulaceae, this work is an attempt to
elucidate the biological importance of this group as a model for understanding
important biological patterns in EmF. To this end, this dissertation work seeks to
address five key questions; 1) What are the major systematic relationships in the
Russula, Russulaceae, and their placement within Russulales; 2) What are the
biogeographic and host patterns in Russula?; 3) What factors have contributed to
the high diversification of Russula?; 4) What are the functional differences
between major groups within Russulaceae? 5) To what extent have members of
Russulaceae retained the ability to decompose soil organic matter?
To address these main questions, my research has combined the
collection and study of sporocarps with molecular phylogenetics and
contemporary evolutionary analytics. These efforts have led to the first multigene
phylogeny of the genus Russula with a clade-based classification system
proposed. By applying ancestral area reconstruction methodologies and
diversification analyses using state speciation-extinction (SSE) models, I have
inferred a temperate origin associated with angiosperms for Russula. In support
of the reversed latitudinal diversity gradient pattern of EmF, I have provided
support for a higher net diversification rate in temperate species of Russula that
is not a result of migration. Here I present an early molecular systematic revision
of the Roseinae clade and provide support for at least 5 new species. Finally, in a
comparative genomic analysis I show that Russulaceae is widely diverse in gene
content, indicating diverse functional roles.