Currie, Cameron R*. Evolutionary ecology of ancient agriculture in ants. In: International Meeting on "Population and Evolutionary Biology of Fungal Symbionts", Ascona, Switzerland, 2007. AB-32. Click here to download the presentation on pdf format.

The fungus-growing ant–microbe symbiosis is a paradigmatic example of coevolution between microbial symbionts and their hosts resulting in unique innovations and a high degree of biological complexity.  The ants tend their fungal mutualist (Basidiomycota: mostly Lepiotaceae), providing it with optimal conditions for growth.  In exchange, the fungus serves as the main food source for the ants.  The origin of this mutually beneficial interaction is likely more than 45–65 million years ago, and the subsequent evolutionary history of this ancient mutualism has resulted in complex associations.

In addition to the ants and their fungal crops, the gardens of fungus-growing ants are host to specialized and virulent fungal pathogens in the genus Escovopsis (Ascomycota: Hypocreales).  Extensive molecular phylogenetic analyses of the garden pathogen reveal both an early origin and tightly coevolved relationship with the ants and their fungal mutualist. To deal with the pathogen the ants have evolved a mutualistic association with filamentous bacteria (actinomycetes) that produce antibiotics that suppress the growth of Escovopsis.  The mutualism between fungus-growing ants and their antibiotic-producing actinomycetes also has an early origin. Fungus-growing ants have evolved elaborate modifications to house and maintain their antibiotic-producing mutualist.  These modifications include crypts that house the bacteria, tubercles (integumental protrusions) present within crypts or directly on the cuticle, and previously unknown exocrine glands connected to tubercles through cuticular channels. Recent experimental and molecular ecology work indicating the presence of additional integral symbionts within this symbiosis will be presented, as well as research that supports the idea that the attine ant-microbe symbiosis is an ancient coevolutionary ‘arms race’ between the garden parasite, Escovopsis, on the one hand, and the tripartite mutualism on the other.

Keywords: mutualism, coevolution, cooperation, conflict, parasites

*Institution: University of Wisconsin-Madison

Email: currie@bact.wisc.edu