The Herpotrichiellaceae (Chaetothyriales) is another example of a major fungal lineage derived from a lichenized ancestor that gave rise to opportunistic pathogens to humans. Fonsecaea pedrosoi is one of the causative agents of chromoblastomycosis (a skin disease), and certain species of Exophiala are pathogens of fish, including salmon.

Clues for further study

Better insight into animal and human diseases caused by fungi may be derived from studying the distinction between fungi that never formed lichen symbioses during their evolution and those that had but later lost the ability to form lichens.

The authors go on to speculate why other important fungal species might be found within this secondarily derived non-lichen-forming category of fungi. When a fungus loses its ability to form a lichen symbiosis, some of the genes involved in that process may be diverted to new functions that inadvertently offer possible benefits or detriments to humans, says Mark Pagel, PhD, co-author and professor at the School of Animal and Microbial Sciences of the University of Reading (UK).

Lichens are obligate mutualistic symbioses between fungi (mycobiont) and green algae or cyanobacteria, or with both types of photobionts. They grow on many different substrates such as rocks, soils or trees, and in dry to aquatic habitats from the tropics to the poles. About one-fifth of all known fungi currently in existence form lichens.

Years ago, scientists thought that lichen-forming fungi were a sideshow, a small closely knit fringe group. This study demonstrates that lichen-forming fungi originated much earlier than previously thought. Therefore, the lichen symbiosis has played a larger than expected role in the evolution of fungi. One of the consequences of this early origin is that several major lineages of non-licheni
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Contact: Greg Borzo
gborzo@fieldmuseum.org
312-665-7106
Field Museum
20-Jun-2001