Ophiocordyceps unilateralis: A keystone species for unraveling ecosystem functioning and biodiversity of fungi in tropical forests?

Ophiocordyceps unilateralis (Ascomycota: Hypocreales) is a specialized parasite that infects, manipulates and kills formicine ants, predominantly in tropical forest ecosystems. We have reported previously, based on a preliminary study in remnant Atlantic Forest in Minas Gerais (Brazil), that O. unilateralis represents a species complex. On each of the four species of infected carpenter ant (Camponotus) collected, the fungus-characterized macroscopically by a single stalk arising from the dorsal neck region on which the sexual structures (stromatal plates) are borne laterally-can readily be distinguished both microscopically and functionally. Here, we describe and discuss the biology, life cycle and infection strategies of O. unilateralis s.l. and hypothesize that there may be hundreds of species within the complex parasitizing formicine ants worldwide. We then address the diversity within related hypocrealean fungi, with particular reference to symbionts (mutualists through to parasites), and argue that the widely-quoted total of extant fungi (1.5 million species) may be grossly underestimated.