Fungus-growing ants

Fungus-growing ants (subtribe Attina) comprise all the known fungus-growing ant species participating in ant-fungus mutualism. They are known for cutting grasses and leaves, carrying them to their colonies' nests, and growing fungi on them which they later feed on. Their farming habits typically have large effects on their surrounding ecosystem. Many species farm large areas surrounding their colony and leave walking trails that compress the soil and no longer grow plants. Attine colonies commonly have millions of individuals, though some species only house a few hundred. They are the sister group to the subtribe Dacetina. Leafcutter ants, including Atta and Acromyrmex, make up two of the genera. Their cultivars mostly come from the fungal tribe Leucocoprineae of family Agaricaceae. Attine gut microbiota is often not diverse due to their primarily monotonous diets, leaving them at a higher risk than other beings at certain illnesses. They are especially at risk of death if their colony's fungus garden is affected by disease, as it is most often the only food source used for developing larvae. Many species of ants, including several Megalomyrmex, invade fungus-growing ant colonies and either steal from and destroy these fungus gardens, or they live in the nest and take food from the species. Fungus-growing ants are only found in the Western Hemisphere. Some species stretch as far north as the pine barrens in New Jersey, USA (Trachymyrmex septentrionalis) and as far south as the cold-deserts in Argentina (several species of Acromyrmex). This New World ant clade is thought to have originated about 60 million years ago in the South American rainforest. This is disputed, though, as it appears that they likely evolved in a drier habitat while still learning to domesticate their crops. Early ancestors of Attine ants were probably insect predators. It is likely that they began foraging for leaf sections, but then converted their primary food source to the fungus these leaf cuts grew. Higher attines, like Acromyrmex and Atta are believed to have evolved in Central and Northern America about 20 MYA, starting with Trachymyrmex cornetzi. While the fungal cultivars of the 'lower' attine ants can survive outside an ant colony, those of 'higher' attine ants are obligate mutualists, meaning they cannot exist without one another. Generalized fungus farming in ants appears to have evolved about 55-60 million years ago, but early 25 MYA ants seemed to have domesticated a single fungal lineage with gongylidia to feed colonies. This evolution of using gongylidia appears to have developed in the dry habitats of South America, away from the rainforests where fungus-farming evolved. About 10 million years later, leaf-cutting ants likely arose as active herbivores and began industrial-scaled farming. The fungus the ants grew, their cultivars eventually became reproductively isolated and co-evolved with the ants. These fungi gradually began decomposing more nutritious material like fresh plants. Shortly after Attine ants began keeping their fungus gardens in dense aggregations, their farms likely began suffering from a specialized genus of Escovopsis mycopathogens. The ants evolved cuticular cultures of Actinobacteria that suppress Escovopsis and possibly other bacteria. These cuticular cultures are both antibiotics and antifungals. The mature worker ants wear these cultures on their chest plates and sometimes on their surrounding thorax and legs as a biofilm.