Ant–fungus mutualism

Ant–fungus mutualism is a symbiosis seen in certain ant and fungal species, in which ants actively cultivate fungus much like humans farm crops as a food source. In some species, the ants and fungi are dependent on each other for survival. The leafcutter ant is a well-known example of this symbiosis. A mutualism with fungi is also noted in some species of termites in Africa.

Fungus-growing ants actively propagate, nurture and defend the basidiomycete cultivar. In return, the fungus provides nutrients for the ants, which may accumulate in specialized hyphal-tips known as "gongylidia". In some advanced genera the queen ant may take a pellet of the fungus with her when she leaves to start a new colony.

There are five main types of agriculture that fungus-growing ants practice: lower, coral fungi, yeast, generalized higher, and leafcutter agricultural systems. Lower agriculture is the most primitive system and is currently practiced by 80 species in 10 genera. Coral-fungus agriculture is practiced by 34 species by a single derived clade within the genus Apterostigma. The coral fungus farmers underwent a switch of cultivars between 10 and 20 million years ago to a non-leucocoprineacoeous fungus, which makes its choice of cultivar different from all other attines. Yeast agriculture is practiced by 18 species of Cyphomyrmex rimosus. The C. rimosus group is hypothesized to have evolved growing fungus in a yeast form between 5 and 25 million years ago. Generalized higher agriculture is practiced by 63 species in two genera and refers to the condition of highly domesticated fungus. The fungi used in higher agriculture cannot survive without its agriculturalists to tend it and has phenotypic changes that allow for increased ease of ant harvesting. Leafcutter agriculture, which is a more highly derived form of higher agriculture, is practiced by 40 species in two genera and has the most recent evolution, originating between 8 and 12 million years ago. Leaf cutters use living biomass as the substrate to feed their fungi, whereas in all other types of agriculture, the fungus requires dead biomass.

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