Hold Your Horses: Ants farm too?
Do you know which characteristics differentiate humans from other animals? One thing is for sure, it is not farming. Ants have been cultivating their own fungi farms for millions of years now. There are nearly 240 discovered species that follow this behavior, and they are known as attine, or fungus farming, ants. The most well known is the leafcutter ant.
A farmer ant drawing.
How do ants actually cultivate these farms? Depending on the species, an ant may be classified as a higher or lower attine ant. Higher attine ants farm fungi that are completely dependent on the ants for survival whereas lower attine ants farm fungi that can also be found in the wild. Ants bring material they cannot digest themselves, such as pieces of leaves and decomposing organic matter, to their underground nests. They grow their fungi on a platform of rootlets, tiny branches that form from main roots in the ground. These spaces are kept clean and isolated to prevent weed and harmful fungi from contaminating the crops. Before ants work in their farms, they use the fine hair on their legs as a comb to clean each of their limbs and antennae. They also have a mutualistic relationship with bacteria that produce antibiotics, which are then used as a form of pesticide repellent. When a colony relocates, the queen ant takes a piece of the fungus to regrow in the new nest.
A research team of evolutionary biologists and ecologists constructed a phylogenetic tree for ants and fungi. With this tool, they were able to pinpoint time periods that ants began to farm. These scientists found this agricultural trait may be linked to the dinosaurs! 66 million years ago, an asteroid collided into Earth, lifting tons of debris into the atmosphere. This collision blocked sunlight from reaching the surface, which caused dinosaurs and many other organisms dependent on sunlight to go extinct. Ants and fungi, however, are small organisms that often live underground without sunlight. As photosynthetic plants decayed, fungi grew rapidly. Scientists believe that ants took advantage of this event by learning to farm fungi.
About 27 million years ago, certain species of fungi became fully domesticated. This adaptation occurred during a phase known as global cooling, a period of intense droughts in South America. Ants transported their fungi farms as they reallocated into new habitats. Fungi were removed from their wet habitats and brought into dry environments. As a result, these fungi species grew genetically isolated and dependent on these ants, now known as higher attine ants, for survival. This change in environment, however, also altered the genetic structure of these attine ants. These ants evolved to no longer make arginine, a compound used to make proteins, in their cells. Because fungi provide arginine, attine ants are dependent on them as well. One well-known example of this mutually dependent relationship is the fungi Leucoagaricus gongylophorus species grown by the leafcutter ants.
A leafcutter ant gathering leaf pieces.
Although farming may mark the beginning of human civilization, ants have been farming crops for millions of years. There could be a colony of ants farming in your own backyard!
Media Credits:
[1]: Drawn by author.
[2]: Photo by Rain Forest Alliance.
https://www.rainforest-alliance.org/ja/species/leafcutter-ant/
Further Reading:
Currie, C., Scott, J., Summerbell, R. et al. Fungus-growing ants use antibiotic-producing bacteria to control garden parasites. Nature 398, 701–704 (1999). https://doi.org/10.1038/19519
Dejean, A., Azémar, F., Naskrecki, P., Tindo, M., Rossi, V., Faucher, C., & Gryta, H. (2023). Mutualistic interactions between ants and fungi: A review. Ecology and evolution, 13(8), e10386. https://doi.org/10.1002/ece3.10386
Ted R. Schultz et al., The coevolution of fungus-ant agriculture. Science 386,105-110 (2024). DOI:10.1126/science.adn7179
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