the hibbett lab

at Clark University

People Connected to the Hibbett Lab

David Hibbett

Portrait by a Clark student in Introductory Biology.

Bio: I received a bachelors degree from the Botany Department of UMass Amherst in 1985, and a Ph.D. from the Botany Department of Duke University in 1991, under the direction of Rytas Vilgalys. I spent one year (1991-1992) as a Science and Technology Agency of Japan Post-doctoral Fellow at the Tottori Mycological Institute (Tottori, Japan), under the direction of Akihiko Tsuneda. In the Spring semester of 1993, I taught microbiology at Framingham State College (Framingham, Massachusetts). From1993-1999, I was a post-doc then research associate in the laboratory of Michael Donoghue in the Harvard University Herbaria. I joined the faculty of Clark University in Sept., 1999.

Research interests: I have diverse interests in fungal evolutionary biology, with the unifying theme being phylogeny. I am a participant in the NSF-sponsored projects Deep Hypha (a Research Coordination Network of systematic mycologists) and AFTOL (Assembling the Fungal Tree of Life). AFTOL is a collaborative, kingdom-wide phylogenetic study of fungi. My laboratory’s part in AFTOL is to coordinate the sampling of molecular data in the basidiomycetes.

For more details about my research, see my list of Publications, as well as the lab's Current Research page.

Following are brief sketches introducing the main subject areas that interest me:

Phylogeny, diversity, and classification of homobasidiomycetes. The homobasidiomycetes include the mushroom-forming fungi. There are about 16,000 described species in this group, but this is surely a gross underestimate of its actual diversity. Beginning with my dissertation research with Rytas, I have been developing molecular data sets for inferring the higher-level phylogenetic relationships of this group. With my colleague R. Greg Thorn (University of Western Ontario), I proposed a “preliminary phylogenetic outline” for the homobasidiomycetes, based on a synthesis of published and unpublished molecular studies. Greg and I suggested that there are at least eight major clades of homobasidiomycetes. An analysis using four regions of rDNA by Manfred Binder and me found strong support for seven of these clades, but one group, the “polyporoid clade”, remains weakly supported. Recent studies by workers such as Ellen and Karl-Henrik Larsson (University of Gothenburg, Sweden), Ewald Langer (University of Kassel, Germany), and others now suggest that there may be additional clades that Greg and I did not recognize. However, these views are generally based on only one region, the large-subunit nuclear rDNA. Currently, and as part of the AFTOL project, my lab is developing multi-gene datasets to improve our understanding of the phylogenetic relationships of homobasidiomycetes.

Evolution of fruiting body form in homobasidiomycetes. I was initially drawn to the homobasidiomycetes by the incredible diversity of their fruiting bodies, which include gilled mushrooms, coralloid forms, puffballs, polypores, stinkhorns, bird’s nest fungi, and others. Much of my research on evolution of these forms has involved molecular phylogenies, with character-state transformations “mapped”on using parsimony. Recently, I have begun to use binary and multi-state maximum likelihood methods, both to estimate ancestral states and determine if there are trends in the evolution of fruiting body forms. I have been particularly interested in the evolution of “resupinate” forms, which lie flat on their substrates.

In addition to phylogeny-based studies, my work on morphological evolution has  also included comparative developmental morphology and paleomycology. The developmental work was done during my first post-doc, at the Tottori Mycological Institute. I compared the ontogeny of the hymenophore in the gilled mushrooms Lentinus and Panus, which Pegler had lumped into a single genus Lentinus. The ontogenies in the two groups were strikingly different, supporting their classification in different genera. This work not only generated characters for taxonomy, but also provided insight into the nature of shifts in developmental programs that underlie morphological evolution in fungi. My paleomycological studies have been performed in collaboration with David Grimaldi (American Museum of Natural History) and others. Together, we have described three of the four known fossil agarics. One, Archaeomarasmius leggetti, is from Atlantic Coastal Plain amber, and is the oldest fossil agaric (ca. 90-94 mya). The others, Protomycena electra and Aureofungus yaniguaensis, are from Dominican amber and are much younger (15-25 mya). These fossils are strikingly similar to certain extant forms, suggesting that there have been extensive periods of morphological stasis in some clades of homobasidiomycetes.

Evolution of nutritional modes in homobasidiomycetes. Homobasidiomycetes have diverse means for making a living. They function as saprotrophs (decayers), pathogens, ectomycorrhizalsymbionts, arthropod symbionts, and even lichens. I have used phylogenetic trees to study the shifts in these nutritional modes, focusing on the evolution of the ectomycorrhizal habit and transitions between “brown-rot”and “white-rot” modes of wood decay. My analyses of the evolution of ectomycorrhizae suggest that there have been multiple gains and losses of the ectomycorrhizal habit in homobasidiomycetes. This suggests that “mutualisms”are not necessarily stable endpoints in evolution, and that their breakdown can lead not just to parasitism, but to the complete dissolution of the symbiosis. We are presently developing large datasets of homobasidiomycetes to further explore the evolution of mycorrhizae in this group.

In white-rot, cellulose and lignin are both degraded, leaving the substrate bleached and with a stringy consistency, whereas in brown-rot, the lignin is not appreciably degraded, and the decayed substrate is brown, with a friable consistency. Brown rot is the rarer form in homobasidiomycetes and is associated with bipolar mating systems and growth on coniferous substrates. We used parsimony and maximum likelihood methods to infer the pattern of transformations in decay modes, and evaluate the proposed correlations with mating systems and substrate ranges. Our results suggested that the plesiomorphic condition in homobasidiomycetes is to have white rot, and that there have been multiple origins of brown rot. Both the concentrated changes test and maximum likelihood analyses suggest that the evolution of brown rot may have promoted ashift toward exclusive decay of conifer substrates. No correlation was found with mating systems, however.

One avenue for future research in evolution of nutritional modes concerns the evolution of the gene families that encode lignin-degrading peroxidases. For example, we would like to ask if mycorrhiza-formers and brown and white rot groups of saprotrophs differ in their enzymatic arsenals, or if the rate of evolution and strength of selection on these genes are comparable in both groups. We are also interested in unraveling the history of gene duplication and loss in these genes, which could provide tools for rooting some of the problematical nodes in the homobasidiomycetes (such as the root node of the polyporoid clade).

Evolution of aquatic homobasidiomycetes, and relationships to cyphelloid forms. Recently, Manfred Binder and I became interested in the evolution of marine homobasidiomycetes. We studied phylogenetic relationships of Nia vibrissa, which is a minute marine gasteromycete that has appendaged spores. To our surprise, we discovered that Nia is related to certain cyphelloid fungi, which are minute cup-shaped forms. The fungal genetics lab-rat Schizophyllum commune is also in this clade, along with the very odd “beefsteak fungus” Fistulina hepatica,which makes a large pileus with a hymenophore composed of many individually free tubes. We are presently funded by the NSF to continue our work on cyphelloid and aquatic basidiomycetes.