You've probably seen leafcutter ants carrying pieces of plants perhaps in a nature documentary, in a science museum, or in the song “Endless Cycle” at the beginning of the 1994 Disney animated film “The Lion King.”
These ants don't eat the leaves — instead, they take them back to their nests to feed a fungus garden, which produces food for the ants.
Researchers have now used DNA analysis to find out how long ants have been cultivating fungi, as described in a study published this Thursday (3) in Science magazine . These insects were found to be some of the world's smallest farmers 66 million years ago, thanks in part to the asteroid that hit Earth and set off a chain of events that led to the extinction of the dinosaurs.
Fungi belong to a kingdom of life more closely related to animals than plants, and many of them consume decaying plant matter. Some microorganisms produce fruiting bodies that we know as mushrooms, part of their reproductive cycles, but they also produce a network of branching structures called hyphae.
Exactly 150 years ago, scientists first discovered that leafcutter ants cultivated fungal gardens inside their nests, feeding them pieces of leaves and, in return, eating the tips of the fungal webs.
“These insects practice agriculture just like humans,” said the study's lead author, Dr. Ted R. Schultz, research entomologist and curator of hymenoptera at the Smithsonian's National Museum of Natural History in Washington, DC. “They have small brains, and yet they can carry out this complex set of behaviors.”
A better understanding of ant farming practices, which have benefited both insects and fungi for millions of years, could, according to Schultz, one day help humans develop more effective farming methods.
Farmer ants grow fungus gardens
Schultz has been studying fungus-farming ants, including leafcutter ants, for more than 35 years to try to understand how this unusual behavior evolved.
To trace the evolution of this relationship between these insects and microorganisms, Schultz and his colleagues constructed complex family trees.
Using DNA from 475 species of fungi, including 288 species known to be cultivated by ants, researchers pieced together how all these organisms are related. The study team did the same with 276 animal species, including 208 fungus-farming ants.
Family trees are based on the similarities or differences between the genomes of different groups, and the length of the trees' branches is determined by the amount of genetic change from one species to another.
These differences are often linked to time, with more variation requiring more time to evolve. By matching each family tree with rare fossils of fungi and ants, scientists were able to determine how long ago these insects and microorganisms branched into the families and species that exist today.
Researchers found that the ancestors of modern fungi cultivated by ants began evolving 66 million years ago — around the same time that a massive asteroid collided with what is now the Yucatan Peninsula in Chicxulub, Mexico.
The dust cloud from the impact blocked sunlight, causing a dramatic extinction of plants and animals, including dinosaurs (except birds). But this destruction and decomposition appears to have been a golden opportunity for the fungi that decomposed the dead plants.
“There is evidence that fungi proliferated briefly shortly after the Cretaceous-Paleogene event,” Schultz said.
The ancestors of modern leafcutter ants and other fungus-farming ants also diversified around this time, and appear to have co-evolved with fungi over the years, to the point where some ants have “domesticated” species that today are found only in nests. of these insects.
Dr. Corrie Moreau, professor of entomology and evolutionary biology at Cornell University in New York state, agrees with Schultz's hypothesis that the asteroid impact led to the evolution of fungal farming in ants.
“It's one of those things that they can never prove unless we get a time machine, but they align what was happening in microorganisms and insects with what was occurring globally,” said Moreau, who was not involved in the study. “You can see this almost one-to-one relationship.”
Mutually beneficial ties
This shared evolutionary history appears to have benefited both ants and fungi in a phenomenon known as mutualism. Animals get food, and microorganisms get shelter and care, as well as the chance to spread as insects colonize new territories.
“When a daughter queen gets ready to leave her mother's nest and start her own nest, she takes some of her mother's fungus in her mouth,” Schultz explained.
The organisms help each other, but they may also help human farmers in the future.
“Humans have been farming for 12,000 years,” Schultz said. “The ants, for 66 million years.”
These insects utilize beneficial bacteria to keep their fungal crops healthy and appear to have more success than human farmers often have with their crops.
“We are constantly dealing with antibiotic resistance and trying to find new drugs to overcome it,” Schultz said. “If we can figure out how they've been doing it, I don't see why it couldn't inform the practice of human agriculture and improve it.”
This content was originally published in Agricultura das ants appeared with asteroid that extinguished dinosaurs, says study on the CNN Brasil website.
Source: CNN Brasil