When a huge asteroid wiped out the dinosaurs, the ants started growing fungi

Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news of fascinating discoveries, scientific advances and more.

CNN
—

You’ve probably seen leafcutter ants carrying bits of plants, perhaps in a nature documentary, at a science museum or on… “Circle of Life” song. At the beginning of the 1994 Disney animated film The Lion King.

These ants do not eat leaves, but rather bring them back to their nests to feed a garden of fungi that produce food for the ants.

Researchers have now used DNA analysis to reveal how long the ants have been cultivating the fungus, which has now been described in a file Study published Thursday In Science magazine. It turns out that these insects were some of the world’s youngest farmers 66 million years ago, thanks in part to an asteroid that struck Earth and set off a chain of events that led to the extinction of the dinosaurs.

Fungi are a kingdom of life more closely related to animals than to plants, and many of them consume decaying plant matter. Some fungi form the fruiting bodies we know as mushrooms as part of their reproductive cycles, but they also produce a branching network of filamentous structures called Threads. Exactly 150 years ago, scientists first discovered that leafcutter ants were growing fungal gardens inside their nests, feeding off pieces of fungi from the leaves and in turn eating the tips of the fungal networks.

“Ants farm just like humans,” said the study’s lead author. Dr. Ted R. Schultzresearch entomologist and curator hymen At the Smithsonian National Museum of Natural History in Washington, DC. “They have small brains, and yet they manage to carry out this complex set of behaviors.”

A better understanding of the ant-rearing practices that have benefited insects and fungi throughout the ages could one day help humans develop more efficient agricultural methods, according to Schultz.

Schultz has been studying fungus-farming ants, including leaf cutters, for more than 35 years to try to figure out how this unusual behavior evolved.

To trace the evolution of this relationship between ants and fungi, Schultz and his colleagues built complex family trees. Using DNA from 475 species of fungi, including 288 species known to be cultivated by ants, the researchers pieced together how all these organisms are related to each other. The study team did the same with 276 species of ants, including 208 species of fungus growers.

Family trees are based on how similar or different the genomes of different species are, and the lengths of tree branches are determined by the amount of genetic variation there is from one species to another. These genetic differences are often related to time, as more diversity requires more time to evolve. By combining each family tree with rare fossils of fungi and ants, respectively, scientists were able to ascertain how long ago ants and fungi branched off into the families and species living today.

The researchers found that the ancestors of modern ant-grown fungi began evolving 66 million years ago, the same time a massive asteroid collided with what is now the Yucatan Peninsula in Chicxulub, Mexico. The dust cloud resulting from the impact blocked sunlight, causing significant death to plants and animals, including dinosaurs (except birds). But it seems that this destruction and decay was a golden opportunity for fungi that decompose dead plants.

“There is already evidence that fungi spread briefly immediately after the end of the Cretaceous-Paleogene,” Schultz said.

The ancestors of modern leaf cutters and other fungi-farming ants also diversified around this time, and they appear to have evolved alongside fungi over the years to the point that some ants “domesticated” species of fungi that today are found only in ant nests.

Dr. Corey MorrowThe professor of entomology and evolutionary biology at Cornell University in upstate New York agreed with Schultz’s hypothesis that the asteroid impact led to the evolution of fungal cultivation in ants.

“It’s one of those things they can never prove unless we get a time machine, but they connect what was happening with the fungi and the ants to what was happening globally,” said Morrow, who was not involved in the study. “You can almost see this connection between two people.”

This shared evolutionary history appears to have benefited both ants and fungi in what is called mutualism. The ants get food, the fungi get housing and food, as well as the ants’ careful care and the opportunity to spread when insects invade new areas.

“When the daughter queen prepares to leave her mother’s nest and start her own, she takes a bit of her mother’s mushrooms into her mouth,” Schultz said.

Ants and fungi help each other, but they may be able to help human farmers, too.

“Humans have been farming for 12,000 years,” Schultz said. “Ants for 66 million years.”

Ants use beneficial bacteria to keep their fungal crops healthy from disease and appear to have more success than human farmers often do with their crops.

“We are constantly dealing with antibiotic resistance and trying to find new antibiotics to overcome that,” Schultz said. “If we could figure out how they were doing it, I don’t see how that couldn’t enrich and improve the practice of human agriculture.”

Kate Golembiewski He is a freelance science writer based in Chicago with interests in zoology, thermodynamics, and death.