Leafcutter ants and their fungus gardens
Wait, leafcutter ants have gardens? That's right! Ants are one of the only four animals that have evolved agricultural systems (along with humans, bark beetles, and termites). In fact, ant agriculture originated around 50 million years ago, long before human agriculture even developed! (1)
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Leafcutter ants cultivate and grow fungus gardens from Leucoagaricus species, a type of basidiomycetes fungi (2). The ants provide the fungus with freshly cut leaves and plant material, and the fungus provides the ants with food. Together they form a symbiotic relationship, where both are dependent on the other to survive.
Schultz, T. R., & Brady, S. G. (2008). Major evolutionary transitions in ant agriculture. Proceedings of the National Academy of Sciences, 105(14), 5435–5440. https://doi.org/10.1073/pnas.0711024105
Aylward, F. O., Currie, C. R., & Suen, G. (2012). The Evolutionary Innovation of Nutritional Symbioses in Leaf-Cutter Ants. Insects, 3(1), 41–61. https://doi.org/10.3390/insects3010041
Escovopsis is a fungal pathogen that attacks the ant's fungal gardens. It has been around for as long as the ants and their fungal gardens and has been co-evolving alongside them in an evolutionary arms race ever since. This means that ants have been evolving mechanisms to get rid of Escovopsis from their fungal gardens while Escovopsis has been evolving ways around those mechanisms to persist.
How do leafcutter ants deal with Escovopsis and other pathogens?
Leafcutter ants have evolved many different mechanisms in order to prevent
Escovopsis from damaging their fungal gardens. One of the most important ways ants deal with Escovopsis is through their hygienic behaviors.
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Wait a minute- ants have hygienic behaviors? They sure do! Ants are very clean and organized little critters. They are eusocial insects and have their own roles within the ant colony based on a caste system, which is determined by ant size:
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the maxima (7-9mm)
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foragers​
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go out and find the leaves
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the soldiers (>9mm)
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​help defend the colony
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the minima (1.6-3mm)
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​garden workers
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care for the fungus garden
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the media (4-6mm)
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​general workers
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cut and prepare the leaves
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Weber, N. A. (1972). The Fungus-culturing Behavior of Ants. Integrative and Comparative Biology, 12(3), 577-587. https://doi.org/10.1093/icb/12.3.577
Worker Ants
Soldier Ants
Queen Ant
The caste system allows ants to split up all the work they have to do, allowing for better efficiency. Each of these jobs is essential for the survival of the ant colony. The minima workers spend most of their time in the fungus garden, caring for the fungal cultivar. As such, they are responsible for cleaning and grooming the fungus to protect against pathogens and other unwanted organisms.
Image modified from Sarefo & Gamekeeper, 2008.
However, while the minima ants are around the fungus garden the most, it is the maxima ants that demonstrate the most hygienic and grooming behaviors (4). This is because they need to leave the ant colony to go out and forage to do their jobs. Upon returning, it is very important for them to clean themselves off to prevent from spreading outside pathogens to their fungus garden. Additionally, some of the smaller ants may even ride on top of these foraging ants to help with the cleaning process to further prevent any possible pathogens from entering the colony.
Richard, F.-J., & Errard, C. (2009). Hygienic behavior, liquid-foraging, and trophallaxis in the leaf-cutting ants, Acromyrmex subterraneus and Acromyrmex octospinosus. Journal of Insect Science, 9(1), 63. https://doi.org/10.1673/031.009.6301
Photo of a small ant helping clean off a leaf being brought back to the colony by a larger foraging ant
Literature Cited
1. Schultz, T. R., & Brady, S. G. (2008). Major evolutionary transitions in ant agriculture. Proceedings of the National
Academy of Sciences, 105(14), 5435–5440. https://doi.org/10.1073/pnas.0711024105
2. Aylward, F. O., Currie, C. R., & Suen, G. (2012). The Evolutionary Innovation of Nutritional Symbioses in Leaf-
Cutter Ants. Insects, 3(1), 41–61. https://doi.org/10.3390/insects3010041
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3. Weber, N. A. (1972). The Fungus-culturing Behavior of Ants. Integrative and Comparative Biology, 12(3), 577-
587. https://doi.org/10.1093/icb/12.3.577
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4. Richard, F.-J., & Errard, C. (2009). Hygienic behavior, liquid-foraging, and trophallaxis in the leaf-cutting ants,
Acromyrmex subterraneus and Acromyrmex octospinosus. Journal of Insect Science, 9(1), 63. https://doi.org/10.1673/031.009.6301
Photos
1. Mukherjee, S. (2023, May 16). Symbiosis - Definition, Types, Examples, and Diagram. Science Facts.
https://www.sciencefacts.net/symbiosis.html
2. Custodio, B.C., Rodrigues, A. (2019). Escovopsis kreiselii specialization to its native hosts in the fungiculture of
the lower attine ant Mycetophylax morschi. Antonie van Leeuwenhoek 112, 305–317. https://doi.org/10.1007/s10482-018-1158-x
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3. Sarefo. Modified by Gamekeeper. (2008, June 8). Atta.cephalotes.gamut. Wikipedia.
https://en.m.wikipedia.org/wiki/File:Atta.cephalotes.gamut.selection.jpg
4. Bertner P. (2010, Sep 12). Leafcutter ant (Atta sp.) minor and major. Flickr.
https://www.flickr.com/photos/rainforests/4984679487
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