Dinosaur extinction led to the emergence of ‘ant agriculture’

The catastrophic event that wiped out the dinosaurs some 66 million years ago wasn’t all doom and gloom – it also set the stage for a remarkable mutualistic relationship between certain ants and fungi. 

The meteor impact that led to mass extinctions created an environment ripe for fungi that thrive on organic matter, which was in abundance as plants and animals perished. 

This opened the door for the ancestor of modern leafcutter ants to begin cultivating fungi, according to a new study published in the journal Science.

Origin of ant agriculture

“The origin of fungus-farming ants was relatively well understood, but a more precise timeline for these microorganisms was lacking,” explained André Rodrigues, a professor at the Institute of Biosciences at São Paulo State University (IB-UNESP). 

“The work provides the smallest margin of error to date for the emergence of these fungal strains, which were previously thought to be more recent.”

Rodrigues coordinates the project “Collaborative research: Dimensions US-São Paulo: integrating phylogeny, genetics, and chemical ecology to unravel the tangled bank of the multipartite fungus-farming ant symbiosis,” supported by the São Paulo Research Foundation (FAPESP) collaboration with the U.S. National Science Foundation (NSF). 

Evolutionary line of fungi

The research team made their breakthrough by analyzing ultraconserved elements (UCEs) in the genomes of 475 fungal species cultivated by ants. UCEs are genetic regions that remain stable across species, allowing scientists to trace evolutionary paths.

“In this case, we were interested in the regions close to these elements. They show the most recent differences between species and allow us to trace a fairly accurate evolutionary line,” explained co-author Pepijn Wilhelmus Kooij, a researcher at IB-UNESP.

Fungi farmed by ants

This method enabled the researchers to establish that two distinct fungal lineages, now cultivated by today’s leafcutter ants (known as Attini), emerged almost simultaneously 66 million years ago. 

This discovery provides a clearer timeline for the development of this remarkable mutualism – where ants and fungi depend on each other for survival – occurring tens of millions of years before human agriculture.

The study also identified a second group of fungi, known as coral fungi, which began to be cultivated by ants around 21 million years ago. These fungi form structures resembling tiny coral colonies and represent a fascinating diversification of this ancient relationship.

Ant agriculture expanded under pressure

The research supports the idea that the fungi were already somewhat adapted for mutualism before ant agriculture began. 

“It is likely that the ancestor of the leafcutter ant group lived in close proximity to fungi, possibly feeding on them or their byproducts,” Rodrigues said. 

However, the intense environmental pressure from the meteor impact may have transformed this casual relationship into a full-blown mutual dependency, where the fungi relied on ants for survival and reproduction, while the ants depended on the fungi as a primary food source.

Ants influence the growth of fungi

Today, four different groups of ants cultivate four types of fungi. Some ants even influence the growth of the fungi to ensure they receive specific nutrients. 

“When we cultivate them in the lab, the fungi take the expected form of hyphae. However, inside the colony, one of these hyphae types becomes swollen and forms structures similar to grape clusters, rich in sugars. We still don’t know how the ants do this,” Kooij said.

Nutritional crisis after meteor impact 

Mauricio Bacci Junior, a professor at IB-UNESP and co-author of the paper, noted that the origin of this fungus-farming practice was likely an adaptation to a nutritional crisis faced by the ants after the meteor impact. 

“With the abundance of fungi and fewer food options, ants that already had some relationship with fungi found them to be useful when cultivated,” he explained. 

The fungi decompose organic matter brought by the ants, which in turn consume the substances produced by the fungi that they cannot obtain from other sources. “It’s as if the fungus were the insect’s external stomach,” Bacci said.

Dynamic evolutionary partnership 

After the ants began farming fungi, another evolutionary shift occurred around 27 million years ago with the expansion of the Cerrado, a savanna-like biome. 

The expansion opened more arid areas, which provided a second selective pressure and led to the diversification of leafcutter ants. This adaptation also likely spurred the fungi to evolve and become more efficient at both producing food for the ants and decomposing organic matter.

Today, enzymes produced by the fungi cultivated by ants are being studied for their biotechnological potential. These enzymes not only break down organic material but are also being researched for their ability to degrade other substances, including plastics.

The study sheds new light on the complex and ancient relationship between ants and fungi, revealing a dynamic evolutionary partnership that has existed for millions of years.

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