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.
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.
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.
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.
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.; São Paulo Research Foundation; 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.