Concept
The ant–fungus mutualism is a symbiosis seen between certain ant and fungal species, in which ants actively cultivate fungus much like humans farm crops as a food source. There is only evidence of two instances in which this form of agriculture evolved in ants resulting in a dependence on fungi for food. These instances were the attine ants and some ants that are part of the Megalomyrmex genus. In some species, the ants and fungi are dependent on each other for survival. This type of codependency is prevalent among herbivores who rely on plant material for nutrition. The fungus’ ability to convert the plant material into a food source accessible to their host makes them the ideal partner. The leafcutter ant is a well-known example of this symbiosis. Leafcutter ants species can be found in southern South America up to the United States. However, ants are not the only ground-dwelling arthropods which have developed symbioses with fungi. A similar mutualism with fungi is also noted in termites within the subfamily Macrotermitinae which are widely distributed throughout the Old World tropics with the highest diversity in Africa. Fungus-growing ants actively propagate, nurture, and defend Lepiotaceae and other lineages of basidiomycete fungus. In return, the fungus provides nutrients for the ants, which may accumulate in specialized hyphal-tips known as "gongylidia". These growths are synthesized from plant substrates and are rich in lipids and carbohydrates. 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 three castes of female worker ants in Attini colonies which all participate in foraging plant matter to feed the fungal cultivar. The lowest caste, minor, is smallest in size but largest in number and is primarily responsible for maintaining the fungal cultivar for the rest of the colony. The symbiosis between basidiomycete fungi and attine ants involves the fungal pathogen, Escovopsis, and an actinomycetes bacterial symbiont, Pseudonocardia.
