Dinosaurs certainly didn’t benefit from the Chicxulub asteroid impact, but that was a wholly different story for the ancestors of today’s ants. In fact, the climatic upheaval that rocked Earth 66 million years ago may be the major reason some of the insect species learned to farm millions of years before humans even evolved.
In a study published on October 3 in the Science, an international team of researchers from Brazilian and US universities as well as the Smithsonian Institute examined genetic data from hundreds of ant and fungi species to trace their evolutionary trees. After comparing the two timelines, experts then pinpointed when the two began to truly intertwine—around the exact same era that followed the Chicxulub asteroid.
“The origin of fungus-farming ants was relatively well understood, but a more precise timeline for these microorganisms was lacking,” André Rodrigues, a researcher at the Institute of Biosciences of São Paulo State University (IB-UNESP) and paper co-author, said in a statement. According to Rodrigues, the new analysis offers the “smallest margin of error to date for the emergence of these fungal strains, which were previously thought to be more recent.”
Researchers have long understood that debris ejected into the atmosphere by the six-mile-wide space rock created a low-light environment for generations. While a death sentence for 70 percent of all life on Earth, it served as the perfect incubator for certain fungi species that fed on organic matter. At the same time, the plant and animal die-off forced ancient ancestors of today’s leafcutter ant group to rely on cultivating and harvesting the microorganisms.
The key to understanding the origins of fungi-ant mutualism resided in looking at their ultraconserved elements (UCEs)—genomic areas that remain intact throughout the multiple evolutionary generations.
“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,” said Pepijn Wilhelmus Kooij, a IB-UNESP researcher and paper co-author.
It would ultimately take almost 40 million years, however, for ant and fungal species to make the leap to a truly mutualistic relationship. As the Smithsonian explained, a period of rapid cooling approximately 27 million years ago resulted in ants transporting fungi species from wet climates to drier ones, isolating the microorganisms from their native populations. These fungi then became completely dependent on ants for their proliferation and survival. This led to what is known as higher agriculture, in which ants harvest fresh vegetation for their fungi to break down as the plant matter decays. The microorganisms then produce threadlike web structures called hyphae. During this time, the tips of these hyphae grow lipid- and carbohydrate-rich bulbs called gongylidia that the insects use for food. Essentially, ants figured out farming millions of years before humans learned their version of it, much less existed as a species.
[Related: Earth is home to nearly 20 quadrillion ants.]
“The ants domesticated these fungi in the same way that humans domesticated crops,” Ted Schultz, the Smithsonian Institute’s curator of ants and paper lead author, said in the institute’s profile.
“To feed itself, the fungus decomposes the organic matter carried by the ants. In turn, the ant consumes substances produced by the fungus that it couldn’t obtain from any other source,” IB-UNESP professor Mauricio Bacci Junior added in a statement. “It’s as if the fungus were the insect’s external stomach.”
Today, ants’ ability to farm has led to development of diverse fungi species that are both efficient at food production for colonies, as well as decomposing organic matter. These enzymes are so useful that other researchers are investigating how to harness them to safely break down harmful materials like plastics. In the future, humanity’s sustainable recycling solutions may be owed in no small part to some of the planet’s earliest, innovative ants.
