WASHINGTON — The asteroid that wiped out the dinosaurs also brought opportunities for new life. Scientists have found that after the asteroid wiped out many plants, ants started farming fungi to help them survive and get the food they needed in tough times.
The meteor impact 66 million years ago created a low-light environment that allowed fungi that fed on organic matter to survive, as many plants and animals died. Additionally, the dust in the skies made it difficult for plants to undergo photosynthesis — converting light energy to make food. With the spread of fungus, researchers found it allowed fungus-farming ants to thrive in these dark times . The findings preview the start of the mutualistic relationship shared between several fungi species and ants.
“The origin of fungus-farming ants was relatively well understood, but a more precise timeline for these microorganisms was lacking. 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,” says study co-author André Rodrigues, a professor at the Institute of Biosciences of São Paulo State University (IB-UNESP) in Brazil, in a media release. The study is published in the journal Science
Researchers studied the genetic remains of 475 fungal species cultivated by ants from all over the Americas. They narrowed their focus on ultra-conserved elements of the fungal genomes. These regions stay in the genome through the evolution of a group, genetic evidence that links back to the most ancient ancestors
“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,” says study co-author Pepijn Wilhelmus Kooij, a researcher at IB-UNESP supported by FAPESP.
The genetic evidence on fungal species allowed researchers to track two distinct fungal lineages from the same ancestor of present-day leafcutter ants 66 million years ago. The study also showed the emergence of the ancestor of coral fungi, which was cultivated by ants 21 million years ago.
Colony of the species Atta colombica, unearthed in Gamboa, Panama. In the center of the photo, much larger than the workers, is the queen (Credit: Pepijn W. Kooij/IB-UNESP)
In the current study, researchers suggest the ancestor of the leafcutter ants lived close to fungi. The fungi may have been inside any colonies or occasionally collected for food.
Mutualism — a relationship in which both parties benefit — was forced on several fungi species and the ancestor of leafcutter ants. Researchers explain that the asteroid impact made the relationship necessary for survival, with the fungi needing ants for food and reproduction. Ants also used fungi as a significant food source
Nowadays, four different ant groups cultivate four types of fungi. Some insects even influence how the fungi grow so they can produce certain 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 explains.
The authors suggest that cultivating fungi was likely a way for ants to adapt to a nutritional shortage ants faced after the asteroid's impact. Fungi, in turn, found it more helpful when cultivated by ants, creating a mutualistic relationship. The process goes with the fungus breaking down organic matter ants carried over. Afterward, ants eat the products made from the fungus that would not be found in other food sources at the time.
Another major event affected the future of fungus-farming ants. Ants previously lived in humid forests. However, 27 million years ago environmental changes changed the terrain to more savanna-like territories. These dry and vast areas led to more places for fungus-farming ants to roam and eventually diversify into today's leafcutter ants
The diversification of ants also provided an opportunity for fungi to diversify. This made them better at making food for the ants and decomposing organic matter. The way fungi evolved to decompose organic matter efficiently is now being studied as a potential way to decompose other materials like plastics.
Paper Summary
Methodology
The researchers used a method called “phylogenomic analysis” to study the relationship between ants and the fungi they farm. They collected DNA from more than 2000 genes across 475 types of fungi and 276 species of ants. By comparing these genes, they created evolutionary trees (like family trees) that show how ants and fungi have evolved together over millions of years.
They also used fossil records to help figure out when different ant and fungus species first appeared. These trees revealed that ants started farming fungi about 66 million years ago, after a big asteroid impact wiped out many species, but helped fungi thrive.
Key Results
The study found that ants have been farming fungi for about 66 million years. At first, ants just happened to grow fungi by accident, but over time, some fungi became completely dependent on ants for survival, meaning they can't live without them. The researchers discovered that there are different types of ant farming: some ants grow fungi that act more like yeast, while others grow large fungal gardens.
The biggest discovery was that a specific kind of fungus started to rely entirely on ants around 27 million years ago, as ants spread into drier areas. This created a very strong relationship between ants and fungi, where both need each other to survive.
Study Limitations
One limitation of this study is that while the researchers mapped out the evolutionary history of ants and fungi, there are still many species of fungi that haven't been studied yet. This means there could be more to learn about how diverse these farming systems are.
Another challenge is the difficulty in knowing exactly when some species evolved, because the fossil record isn't always complete, and DNA evidence only tells part of the story. Also, the study focused mostly on the fungi that ants farm, but less is known about the other types of organisms in these ecosystems that could also play important roles.
Discussion & Takeaways
The key takeaway from this study is that the relationship between ants and the fungi they farm is very old and complex. This coevolution—where two species influence each other's evolution—has been shaped by big events in Earth's history, like asteroid impacts and climate changes.
The research shows how fungus-farming ants have become experts at agriculture, even more specialized than humans in some ways, since some fungi can no longer survive without their ant farmers. This study helps us understand more about how species evolve together and how important symbiotic relationships (where two species live closely together and depend on each other) are in nature.
Funding & Disclosures
The research was supported by the U.S. National Science Foundation; the Smithsonian; the University of Maryland; Louisiana State Board of Regents; Sistema Nacional de Investigación; Cosmos Club Foundation; Explorer's Club in Washington, D.C.; , D.C.; São Paulo Research Fo; Brazilian Council of Research and Scientific Development; Brazilian Federal Agency for Support and Evaluation of Graduate Education; the Royal Botanic Gardens, Kew; and the Carl Zeiss Foundation.
About Jocelyn Solis-Moreira
Jocelyn is a New York-based science journalist whose work has appeared in Discover Magazine, Health, and Live Science, among other publications. She holds a Master's of Science in Psychology with a concentration in behavioral neuroscience and a Bachelor's of Science in integrative neuroscience from Binghamton University. Jocelyn has reported on several medical and science topics ranging from coronavirus news to the latest findings in women's health.
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