Recent research has revealed that ant colonies started cultivating fungi following an asteroid impact on Earth 66 million years ago. While this catastrophe led to a global mass extinction, it also established favorable conditions for fungi to flourish. Enterprising ants took the initiative to farm these fungi, forming an evolutionary bond that grew closer approximately 27 million years ago and persists today.
Although humans began agriculture thousands of years ago, the practice of farming has existed among various species for millions of years. Several animal groups have been cultivating their own food long before humans came into existence.
A recent study indicates that ant colonies began fungus farming as a result of an asteroid collision with Earth 66 million years ago. This event caused a worldwide mass extinction but simultaneously created optimal circumstances for fungi to prosper. Creative ants started to cultivate the fungi, leading to an evolutionary alliance that became increasingly intertwined 27 million years ago, and this relationship continues to evolve.
In an article published on October 3 in the journal Science, researchers from the Smithsonian’s National Museum of Natural History examined genetic data from a wide variety of fungi and ant species to develop detailed evolutionary diagrams. By contrasting these diagrams, the scientists managed to construct a timeline depicting the evolution of ant agriculture, identifying the moment when ants began to cultivate fungi.
“Ants have been engaged in agriculture and fungus farming far longer than humans have been around,” stated Ted Schultz, an entomologist and curator of ants at the museum, who spearheaded the study. “We could certainly learn from the agricultural achievements of these ants over the past 66 million years.”
About 250 species of ants in the Americas and the Caribbean practice fungus farming. Researchers categorize these ants into four different agricultural systems based on their farming methods. Among them, leafcutter ants represent those using the more advanced technique known as higher agriculture. These ants clip fresh plant material to nourish their fungi, which in turn produces a food source known as gongylidia. This nourishment supports complex leafcutter ant colonies that can consist of millions of individuals.
Having spent 35 years dedicated to investigating the evolutionary ties between ants and fungi, Schultz has undertaken over 30 expeditions across Central and South America to study this relationship in its natural setting. He has also reared leafcutter ants and other types of fungus-farming ants in the lab at the museum. Throughout his career, Schultz and his colleagues have amassed thousands of genetic samples of ants and fungi from tropical regions.
This collection of samples was essential for the new study.
“To effectively identify patterns and reconstruct how this relationship has evolved over time, a large number of ant and fungal cultivar samples are needed,” Schultz explained.
The research team utilized these samples to sequence genetic data for 475 fungi species (288 of which are farmed by ants) and 276 ant species (208 of which practice fungus cultivation)—the most extensive genetic dataset of fungus-farming ants ever compiled. This enabled the researchers to develop evolutionary diagrams for both groups. By contrasting wild fungal species with their domesticated counterparts, they could determine when ants began to use specific types of fungi.
The findings indicated that ants and fungi have been interconnected for approximately 66 million years, coinciding with the time of the asteroid impact at the close of the Cretaceous period. This massive collision filled the atmosphere with dust and debris, preventing sunlight from reaching the earth and halting photosynthesis for years. The ensuing mass extinction led to the disappearance of around half of all plant species on the planet at that time.
However, this disaster turned out to be advantageous for fungi, which thrived by decomposing the abundant dead plant material on the forest floor.
“While extinction events can spell disaster for many organisms, they can be beneficial for others,” Schultz remarked. “During the end of the Cretaceous, dinosaurs struggled, but fungi thrived.”
Many of the fungi that flourished during this time probably fed on decaying leaves and debris, bringing them into close proximity with ants. These insects found a reliable food source in the abundant fungi, continuing to depend on these resilient organisms as life began to recover from the extinction event.
The study also uncovered that nearly another 40 million years passed before ants evolved higher agriculture. The researchers traced the origins of this sophisticated agricultural method back to around 27 million years ago. A rapidly cooling climate altered environments worldwide during this era. In South America, drier regions such as woody savannas and grasslands fragmented extensive wet tropical forests. As ants began moving fungi from moist forests into these arid areas, they isolated the fungi from their wild relatives. This isolation forced the fungi to completely depend on ants for survival in the dry climate, paving the way for the higher agriculture system used by leafcutter ants today.
“The ants domesticated these fungi similarly to how humans have domesticated crops,” Schultz noted. “What’s remarkable now is that we can pinpoint when ants first started cultivating these advanced fungi.”
The new paper was co-authored by several collaborators from the National Museum of Natural History, including Jeffrey Sosa-Calvo, Matthew Kweskin, Michael Lloyd, Ana Ješovnik, and Scott E. Solomon. Researchers from various institutions contributed to the study, including the University of Utah, the Royal Botanic Gardens, Kew, the University of California at Berkeley, and the U.S. Department of Agriculture, among others.
This research received support from organizations such as the U.S. National Science Foundation, the Smithsonian Institution, the University of Maryland, and several Brazilian research institutions.
