Symbiotic fungi – Department of Biology - University of Copenhagen

Fungus-growing ants and termites do not rear just any fungus. When fungus farming independently evolved in the New World ants and the Old World termites ca. 30-50 million years ago, the ancestors of the extant fungus-farmers each domesticated a different and very specific lineage of Basidiomycetes. All fungus-growing termites still farm species of the same lineage (the genus Termitomyces), whereas the fungus-growing ants have remained associated with the Leucocoprini lineage, except for a single secondary switch to a tricholomataceous fungal symbiont.

The fungi of the higher attine ants are specially adapted to feed the ants by producing gongylidia, which grow as clusters called staphylae and are comparable to fungal organs. Derived adaptations of this kind imply that these fungi no longer have free-living close relatives. However, the lower attine ants often rear fungi that are still closely related to free-living species. The attine fungal symbionts are attacked by a specialized fungal parasite that has coevolved with its host. To help control these pests, the ants have domesticated Actinobacteria that they grow on their own body to produce antibiotics. The Termitomyces symbionts of fungus-growing termites do not seem to have virulent co-evolved diseases, but fungal "weeds" of the genus Pseudoxylaria are common, but normally suppressed by the farming termites. Termitomyces also produces specialized organs to feed the termite farmers, the so-called nodules that carry asexual spores that allow the termites to inoculate new fungus garden substrate that they deposit as fecal material.

The phylogenies of the symbionts of both the fungus-growing ants and termites are known. They correspond reasonably well with the genus-level phylogenies of their farming social insect hosts, but there have been some horizontal exchanges of symbionts over evolutionary time across genera. It is interesting that both groups show such similar degrees of intermediate symbiont specificity because the fungus-growing ants acquire their fungal symbiont vertically (so that much higher specificity should have occurred if this process is perfect), whereas most fungus-growing termites acquire their fungal symbionts horizontally (so that specificity could potentially have been absent, except for geographic patterning). Other interesting parallels between the two independent social insect farming systems are that colonies of the same population normally rear a variety of genetically different symbionts, but always only a single clone per colony.

Questions asked

  • How can within-genus horizontal symbiont transmission in fungus-growing ants be relatively common when exchange of symbionts in mature colonies is very difficult because of active (mycelial incompatibility) defences of the resident fungus?
  • How is monoculture fungus farming enforced and maintained?
  • What are the recognition mechanisms that govern the colony-specific associations between the farming social insects and their fungal symbionts?
  • To what extent has enzymatic complementarity between fungal symbionts and the insect digestive systems and bacteria microbiomes evolved, and what is the genetic background of such co-evolution?
  • How do symbiotic fungi use the farming ants to vector enzymes to the new parts of gardens where they are most needed?
  • Does the domestication of fungi generally lead to polyploidy, similar to many of our human crop plants?
  • Why did only few crop diseases of fungus gardens evolve?

Research themes

Termite Fungiculture; Fungus growing ants 

Research tools

Chemical analyses; Genetic analyses; GenomicsLaboratory coloniesMicroscopy; Fieldwork