Where Do Little Mushrooms Come From?

Here's a little find from Volo Bog this weekend:

Split-Gill (Schizophyllum commune), Volo Bog SNA,
Lake Co, IL 2/9/2014

Now for a disclaimer - I don't know mushrooms all that well. Any identifications here are likely to be wrong. But, even if they're wrong, some are really neat-looking:

Coral Fungus (Artomyces pyxidatus), Illinois Beach SP, Lake Co, IL 5/27/2006

Sickener (Russula emetica), Nicolet NF, Oconto Co, WI 8/11/2013



Turkey-tail (Trametes versicolor), Devil's Lake SP, Sauk Co, WI 8/9/2013

Fungi seem like such weird forms of life -- the parts you see are just reproductive structures, while the majority of the critter is just a mass of thread-like hyphae extending into whatever substrate they're living on. (Soil, dead wood, etc.) Most are haploid (one set of chromosomes) except for a brief period while reproducing, and many have a unique dikaryon* stage in their life-cycles. We designate their sexes as + and - (well, we call them mating strains, but it's the same principle), and there are quite a few species that are completely asexual. Even those that do use sexual reproduction reproduce asexually more than they do sexually.

These complications produce some serious challenges to our ideas about speciation; indeed, they challenge most of our species concepts. Quite a few studies have examined the issue. (1, 2, 3)   Many well-known species are found worldwide, and quite a few more across the entire northern hemisphere. In many cases, this may be the result of our moving creatures of all stripes around the globe -- the chestnut blight fungus that wiped out our American Chestnuts is a good example. In some cases, it may be due to the ease with which fungal spores travel on the wind.

On the other hand, Vilgalys & Sun found that some patterns of biogeography in Pleurotus are best explained by ancient vicariance events. (4) This pattern would suggest that fungal species are very long-lived, without much speciation. But many fungi are very host-specific, a trait that lends itself to ecological speciation through host shifts. This pattern has been observed in some fungi. (5)

These difficulties may well lie not in our concepts of species as in our criteria for applying those species. Cryptic** species are species that are essentially indistinguishable by phenotypic traits, requiring molecular tests to tell them apart. Now that DNA testing is getting cheaper, we can expect to find a lot more of these cryptic species groups; we're already finding them in fungi. (6,7,8) So we're likely to find that at least some of those cosmopolitan fungal species are really species complexes of various ages. Given the economic and medical importance of many fungi, this sort of work could have important implications far beyond mycological esoterica. (5, 8)

*Dikaryon means two nuclei: when sexual reproduction does occur, fertilization involves a two-step process. First the two cells merge, then later (sometimes much later) the nuclei merge. So a dikaryotic cell has two nuclei from two parents, with different genetic material.

**Not cryptid species -- those are species that are known or suspected to exist, but for one reason or another haven't been formally described.

(1) Giraud, T., Refrégier, G., Le Gac, M., de Vienne, D. M., & Hood, M. E. (2008). Speciation in fungi. Fungal Genetics and Biology, 45(6), 791-802.

(2) Taylor, J. W., Jacobson, D. J., Kroken, S., Kasuga, T., Geiser, D. M., Hibbett, D. S., & Fisher, M. C. (2000). Phylogenetic species recognition and species concepts in fungi. Fungal genetics and biology, 31(1), 21-32.

(3) Taylor, J. W., Jacobson, D. J., & Fisher, M. C. (1999). The evolution of asexual fungi: reproduction, speciation and classification. Annual review of phytopathology, 37(1), 197-246.

(4) Vilgalys, R., & Sun, B. L. (1994). Ancient and recent patterns of geographic speciation in the oyster mushroom Pleurotus revealed by phylogenetic analysis of ribosomal DNA sequences. Proceedings of the National Academy of Sciences, 91(10), 4599-4603.

(5) Giraud, T., Gladieux, P., & Gavrilets, S. (2010). Linking the emergence of fungal plant diseases with ecological speciation. Trends in Ecology & Evolution, 25(7), 387-395.

(6) Matute, D. R., McEwen, J. G., Puccia, R., Montes, B. A., San-Blas, G., Bagagli, E., ... & Taylor, J. W. (2006). Cryptic speciation and recombination in the fungus Paracoccidioides brasiliensis as revealed by gene genealogies. Molecular biology and evolution, 23(1), 65-73.

(7) Queloz, V., Grünig, C. R., Berndt, R., Kowalski, T., Sieber, T. N., & Holdenrieder, O. (2011). Cryptic speciation in Hymenoscyphus albidus. Forest Pathology, 41(2), 133-142.

(8) Pringle, A., Baker, D. M., Platt, J. L., Wares, J. P., Latge, J. P., & Taylor, J. W. (2005). Cryptic speciation in the cosmopolitan and clonal human pathogenic fungus Aspergillus fumigatus. Evolution, 59(9), 1886-1899.