Millions of years ago, ants made antibiotics

The dawn of agriculture did not rise with Neolithic humans in Mesopotamia. Or in China. Or in the Levant. No, it bloomed in the rainforests of South America some 60 million years ago. And the first farmers were humble ants.

Long before early humans cultivated wheat, barley, lentils and flax, ancient leafcutter ants raised fungus. And like human farmers, the ants had to fend off crop pests, particularly a parasitic fungal disease. “If the fungus dies, the ants die,” said Cameron Currie, a microbial ecologist at the University of Wisconsin-Madison who studies fungal-farming ants and their mutually beneficial relationships with other species.

To fight the pestilence, the ants aligned themselves with a bacteria that produces a chemical capable of subduing the parasite.

Now, Currie and his colleagues have found evidence that suggests that the partnership between ants and antimicrobial bacteria has existed for tens of millions of years. The key clues came from two 20million-year-old ants that were discovered, trapped in amber, in the Dominican Republic.

One of the fossilized ants had specialized pockets on its head, called crypts, that are also seen on modern ants. The crypts are known to house the fungus-protecting bacteria, called actinobacteria. The other ant specimen was entombed with gas bubbles on its body, likely produced by the respiration of the actinobacteria.

“It’s kind of like the ants are walking pharmaceutical factories,” said Currie, who is an author of the study, which appeared last week in the journal Proceedings of the National Academy of Sciences. “This indicates that, like in the way ants predated us in growing crops, they also predated us by tens of millions of years in associating with microbes to produce antibiotics.”

Hongjie Li, an evolutionary biologist in Currie’s lab and the lead author of the study, was inspecting the amber specimens last summer, using a scanning electron microscope at the Smithsonian Institution, when he and his colleagues found signs that the amber ants carried bacteria in a manner similar to modern ants.

The team combined that finding and published data on 69 other ant species to reconstruct the ant’s evolutionary tree. The results indicated that the ants established their partnership with the bacteria tens of millions of years ago, shortly after they developed their fungus-farming abilities.

Don Parsons / Courtesy A fungus-farming ant is covered in white symbiotic bacteria, which the ant relies on to produce antibiotics to protect its garden from a parasitic fungus. Amber specimens indicate that fungus-farming ants have been cooperating with antimicrobial bacteria for tens of millions of years.