The agricultural pathology of ant fungus gardens
Although attine ants derived from a single ancestor (2, 3), extant species impact of parasites on human-cultivated monocultures is used as partial evidence in .. The mutualism between fungus-growing ants and their fungi is parasitized by a. Long before humans started farming, in fact long before humans even existed, the The leafcutter ants, or attine ants, include the genus Atta and they eat a The ants and their fungi form a true symbiosis, with both partners benefiting from the. Mar 25, It turns out ants, like humans, are true farmers. to the most recently evolved and best-known fungus-growing ant species--"leaf-cutter ants.
Ant–fungus mutualism - Wikipedia
Until recently it was hard to classify the fungi that are used by leafcutting ants because the fungi rarely produced spores. Recent work studying the DNA of both the ants and the fungi has shown that different colonies of the same ant often grow different species of fungi, despite the fact that each individual colony only farms a single species of fungus.
There is also some evidence that ants occasionally "steal" a fungus from a neighboring colony. Although most of the fungi grown by the attine ants are unique to the ant colonies, there are two exceptions: This suggests that the fungi were collected by the ants recently.
In one case in Florida a species of ant which was introduced in the s now grows a local Florida fungus in its nest. Presumably the original South American fungus that the ant arrived with died out in Florida, so the ant was forced to find a local replacement. The species Cyatta abscondita is considered the most recent ancestor of all leaf-cutting ants. They fall roughly into three major groups, only G1 having evolved gongylidia.
Some G2 species grow long hyphae that form a protective cover over the nest. Those in G3 are paraphyleticthe most heteregenous, and form the most loose relationships with their cultivators.
The fungi were earlier thought to be propagated by ants purely through clonal vegetative means.
How Ants Became the World’s Best Fungus Farmers | Science | Smithsonian
However considerable genetic variation in the fungi suggests that this may not be the case. While the observed vertical transmission of fungal cultivars  and strong host-symbiont specificity   might suggest a tight coevolutionary relationship, recent phylogenetic analyses suggest this is not the case. Multiple domestications of the same fungus, fungal escape from domestication, or cultivar switching could lead to the observed diffuse coevolutionary pattern.
To resolve the conflict between the theoretical prediction that parasites should exist in the clonal attine fungicultural systems and the widespread yet untested belief that ants maintain their gardens free of parasites, we conducted an extensive examination of fungal parasitism of gardens of attine ants. To assess the diversity and abundance of nonmutualistic filamentous fungi in attine ant gardens, we surveyed gardens tended by diverse attine lineages in central Panama from to In total, the gardens of colonies from 8 attine genera, representing the known phylogenetic diversity of the attines, were sampled for fungal parasites.
Nests were excavated as carefully as possible to ensure minimal disruption to the garden.
Colonies were collected and subsequently maintained in sterile plastic containers with multichamber systems: The ants were permitted to stabilize their garden for 3—5 days after collection before samples were taken. In20 pieces per garden were isolated, and 10 or 12 pieces per garden were isolated in and Pieces were selected from throughout the garden and were placed on potato dextrose agar medium with antibacterial antibiotics Penicillin-G and Streptomycin sulfate under aseptic conditions.
The pieces were monitored daily for the growth of nonmutualistic filamentous fungi; if arising from the inocula, these then were isolated into pure culture.
Ants were not given forage material before isolations, minimizing the possibility of obtaining fungi present only as inoculum from recently added garden substrate. Because the microbes isolated from attine gardens may represent inactive propagules which may overgrow the mutualist only on nutrient agar rather than in situ microbial activity, the long-term and consistent presence of nonmutualistic fungi in attine fungal gardens was examined.How fungus-farming ants might help us develop new antibiotics
Representative species of different attines were maintained in the laboratory in the Botany Department of the University of Toronto to resample for persistent, nonmutualistic fungi including 10 colonies each of Apterostigma cf. Colonies were maintained in the laboratory for a month period. After initial sampling in the field, each colony was resampled every 4—8 weeks. Substrate material provided in the laboratory to ants as forage was confirmed to be free from the common nonmutualistic fungi obtained in the initial field sampling.
Air-sampling of spores of these fungi was conducted near ant colonies in Gamboa by using a standard Biotest-Reuter centrifugal air-sampler Biotest AG, Breieich, Germany.
To reduce the possibility of infections spreading between colonies in the laboratory, instruments were sterilized before each new colony was fed or cleaned. Also, moat, mineral-oil, and physical barriers were used to prevent the ingress spread of mites, which potentially could vector fungal propagules between nests.
Reisolation of a fungus in the laboratory over an extended period of time was interpreted as evidence of chronic presence and growth within a garden. Pathogenicity and Virulence of Garden Contaminants. To determine whether Escovopsis, the most commonly isolated nonmutualistic fungus in the above-mentioned sampling see Resultsis a parasite of attine gardens, the virulence of fungi in this genus was investigated by i monitoring for colonies that have been over-grown by the fungus in the laboratory and field; ii excluding large garden fragments from tending ants to determine whether, in the absence of the garden-tending, Escovopsis erupts and manages to over-grow the fragment; and iii directly inoculating colonies with Escovopsis and monitoring these intentionally infected gardens.
We infected fungal gardens with Escovopsis in the laboratory by using young colonies of A. Incipient colonies were collected in Gamboa, Republic of Panama, 6—8 weeks after the mating flight and were confirmed to be free from Escovopsis.