THE CHEMICAL ECOLOGY OF LICHEN MYCOPARASITES - A REVIEW

Lichenicolous fungi colonize lichens to form a variety of biotrophic a ssociations, and while some 300 genera and 1000 species have been reco gnized, almost nothing is known about their biology. The lichenicolous habit is an unusual one because lichens produce a variety of antibiot ic secondary metabolites that are assumed to protect them from parasit ic attack. This may explain why lichens are rarely parasitized in natu re while nonlichen-forming Ascomycetes are frequently and extensively parasitized. Recent field and laboratory studies of lichen parasites f rom a number of fungal groups indicate that chemistry is indeed involv ed in these interactions. These results indicate that (i) lichenicolou s taxa are better able to degrade lichens than related nonlichenicolou s taxa, (ii) lichen parasites are generally tolerant of lichen seconda ry metabolites, (iii) this tolerance seems to be based in part on the ability of cell wall degrading enzymes of parasites to remain active i n the presence of these lichen secondary metabolites, and (iv) the hos t preferences of some lichen parasites reflect these tolerances. There fore, it appears likely that lichenicolous fungi, which have presumabl y had lengthy coevolutionary histories with lichens, have evolved a un ique mode of nutrition that is based in part on an ability to tolerate lichen defense compounds.