How diverse are the fungi? Educated guesses are variable, and currently range between 1.5 million and 5.1 million. With all that diversity, and so many examples of fungi that intersect with our lives (for some great stories on this, see the Cornell Mushroom Blog) it is incredible how little attention they have received as the subjects of speciation studies. Why? I could chalk it up to the charismatic macrofauna effect, but c’mon – there is a fungus that turns ants into zombies! And then there’s another fungus that prevents that zombie fungus from spreading out of control! The world is full of charismatic fungi. Alternatively, the reason is that as humans we can more or less picture what an animal species is while this is not necessarily so with the fungi - we typically can’t even picture an entire fungal individual.
Among folks who study how species form, there has been a particular lot of attention focused on the role that adaptation to different resources plays in the fracturing of species. It is now being suggested that fungal plant pathogens are incredible model systems for this area of research, as one of the primary ways new plant fungal pathogen species may emerge is by shifting onto new host plant resources. This is interesting for at least two reasons. First, the large amount of theory and research that exists on speciation may be able to help guide plant pathogen researchers at understanding the internal factors controlling host switches in the fungal pathogens. Second, it points speciation researchers towards a myriad of new study systems on which experiments can be done. Tatiana Giraud and colleagues point out in a 2010 article that plant pathogens are full of characteristics that make them great for studying rapid ecological speciation (their hosts provide strong selection, they have lots of offspring which increases both their survival and mutation rate, they mate entirely within the host, they have only a few genes that control host specificity and they can clone themselves to keep themselves going for long periods between mating with another individual).
How rapid is rapid? In one example, a rust fungal species emerged by hybridization IN 1997 to infect a poplar tree that itself is a hybrid (Newcombe et al 2000). Wow! In another recent example, researchers studied a pathogen that infects green coffee berries, and found that it diverged approximately 2200 yrs ago. Although ages longer than the first example, this is still very recent in the realm of speciation examples, and leads me to wonder what else is going on out there in this fast-paced world of fungal speciation. From the perspective of an insect researcher, where experiments can be done but lab rearing is tricky, this is fascinating stuff. Stay tuned, and especially to the Giraud Lab (Ecologie, Systematique et Evolution, Universite Paris-Sud) for more neat work in this area!
Newcombe, G, Stirling, B., McDonald, S., and Bradshaw, H.D., Jr. (2000) Melampsora x columbiana, a natural hybrid of M. medusae and M. occidentalis. Mycological Research 104(3): 261-274.