Research
Fungal research at the University of Tennessee involves two thrusts: 1) examining fungal biodiversity and biogeography; 2) examining patterns of fungal evolution.
The next time you look up the name of a mushroom, look at the name of the person(s) which follows it. Fries? Persoon? Quelet? Kuhner and Romagnesi? Bresadola? All Europeans. The same principle holds when one of the non-American picture books are used to identify an American mushroom collection.
I can remember many conversations with Hesler, Smith and others about whether some American fungus was the same species as that named from Europe. But "theirs" was a little bigger, more yellow, with marginate gills, and on and on. Folklore had it that our Pacific Northwest fungi were more similar to the Europeans than either were to the eastern North American flora.
Compounding the problem is the variation which we can expect of every species WITHIN some geographical area. How much variation should be allowed in a species; is it governed by genes or influenced by climate, temperate and the like, or both.
There are two fundamental ways of determining whether fungi from different geographical regions are the same species. The first is so fundamental that it undergirds all others: carefully examine the fungus itself - the mushroom, the culture, whatever - and compare representatives from all geographical distributions. That's called morphotaxonomy; comparison of sensory characteristics, from color and size, to microscopic measurement and taste (see technicalities: morphotaxonomy).
The second approach requires more work. Required are cultures established from single basidiospores, and paired to ascertain whether geographically separated collections recognize each other and can successfully mate. Such experiments rest on some basic tasks: Basidiospores must be obtained from fruitbodies collected in the field. Spores must germinate under laboratory conditions, and resulting mycelia must participate in mating experiments.
With morphotaxonomy, we understand, "if fungi look different, they ARE different". With a biological species approach, we also comprehend "if they recognize each other and successfully mate, they are the same species," regardless of what they look like.
But these days, there are ways to get even more information about "how species work." One uses the property of all mushroom species to produce various enzymes.These enzymes act for the fungus just as they do for us: enzymes help chemical reactions in the digestion of food or the building of storage materials. But these enzymes are not always identical, and often we see evident differences between mushroom collections by comparing their enzymes via electrophoresis. Electrophoretic differences reflect differences in the underlying genes encoding an enzyme.
Another popular strategy involves DNA. If you were attentive to the O.J. Simpson criminal case, you had your fill of DNA, but you may remember that a person's (or a mushroom's) DNA is far more unique than a fingerprint. So we can manipulate, cut, and decode DNA to gather information about mushroom species, geographically separated populations, or even individuals.
Mycology at the University of Tennessee comprises of two faculty labs. One is supervised by Ron Petersen, the other by Karen Hughes. Together, they combine classic morphological taxonomy, sexual compatibility matings, enzymology, and molecular biology (= DNA).
You will read more (below) about various projects in our labs, some using enzymes, some using DNA as supplements to morphology and compatibility, but the general thrust is the same: we want not only to know more about the identification of "species" (however that term is defined), but more about how species BEHAVE and how species ORIGINATE.
Marasmius
A case in point might help. Scott Gordon (Ph.D., 1995) worked with three species of mushrooms in the genus Marasmius. We had collected and cultured isolates of these species from most of eastern North America and from northern Europe, so we had breeding stock as well as fresh and dried fruitbodies with which to work.
One of Scott's pets was Marasmius scorodonius. It was impossible to distinguish between the collections from North America and Europe, and in fact, even the computer could not sort them geographically when supplied with appropriate morphological data. Additionally, all collections were sexually compatible with all other collections. But when laccase electrophoretic patterns were examined, the North American and European collections were mutually exclusive. It was as though there was a different "enzyme species" on each continent. Conclusion: even though all collections belong to one species, the populations are reproductively isolated and intercontinental populations of M. scorodonius do not interbred IN NATURE. If they never interbreed, then it is only a matter of time until they evolve into two separate morphological and/or biological species.
Marasmius androsaceus is a second example. Again, neither the eye nor the computer could distinguish between the collections from North America versus Europe based on morphology. But sexual compatibility matings clearly showed that one potentially interbreeding group was distributed from northeastern North America through Northern Europe, while another interbreeding group (inter-sterile with the first) seemed limited to the southern Appalachian Mountains. It is little wonder, then, that the two "cryptic species" had very different laccase enzyme patterns. Scott is currently an Assistant Professor at the University of Southern Indiana, Evansville.
Pholiota
Coleman McCleneghan (Ph.D. 1996) looked at the taxonomic complexes surrounding Pholiota spumosa and P. alnicola. The previous best minds had described several species in each complex, but when Coleman mated isolates of collections showing the full spectrum of variation on which the several species had been based, sexual compatibility indicated only a single species from one group, and two from the other. Enzymes pointed in the same direction. Conclusion: while it can be valid to recognize the morphological variants, and even to give them names, this situation does not reflect BIOLOGY, only man-made artificial taxonomy. Coleman is now an Assistant Professor at Appalachian State University in Boone, North Carolina where she continues her work with Pholiota and with Appalachian fungi.
Xeromphalina
Jim Johnson (Ph.D. 1997) examined species within Xeromphalina, a small wood-rotting fungus using morphology and intercompatibility studies. Mating studies revealed an unexpected or cryptic species, closely related to Xeromphalina camponella and differing only by spore size. This cryptic species is present in both North America and Europe and is currently sympatric with X. camponella. Phylogenies for species within the genus were determined from the nuclear ribosomal ITS area and showed the cryptic species as a separate evolutionary branch. Jim is currently a Postdoctoral Fellow at Duke University working with Rytas Vilgalys.
Flammulina
Our latest major project deals with Flammulina, the edible known as Enoki-take. The project brings together Petersen on mating studies, Hughes and Andy Methven on molecular systematics, Scott Redhead on morphology and Nadya Psurtseva on cultural and physiological studies. Preliminary results were reported in Montreal in August, 1997 (See Recent Papers for abstracts). We have identified several morphologically unique and reproductively isolated new species within this genus. Manuscripts are in progress to name these species, to characterize their distributions and habitats and to report their phylogenetic relationships. For two species with an intercontinental distribution, we are investigating the question of intercontinental gene flow using molecular markers.
Future Studies
We have initiated studies with Lentinula boryana isolates from Mexico and the U.S. gulf coast and are using mating studies and Restriction Fragment Length Polymorphisms (RFLPs) to examine population structure and barriers to interbreeding (Petersen and Hughes). We are initiating a large study with Lentinellus as part of PEET-supported studies (Petersen, Methven and Hughes). Student projects include: population structure in Clavicorona pyxidata (Ed Lickey), Psathyrella in the Southern Appalachians (David Sime), population structure in Panellus stypticus and the phylogenetic relationships between Panellus, Tectella and Dictyopannus (Jian-Kang Jin).