Arms race between ants and fungi has echoes of The Last of Us
Insects are fighting off fungal invaders, but the fungi have some tricks up their sleeve
- 10 FEB 2023
- 3:50 PM
- BYCLAUDIA LOPEZ LLOREDA
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There’s an arms race going on between a disease-causing fungus and its host, and it’s not the one portrayed in HBO’s postapocalyptic series The Last of Us. Researchers have found that, with a bit of grooming, ants can help their comrades fight off multiple fungal invaders—but that these fungi have also found a way to fight back. Such battles could influence the evolution of pathogens found in a wide range of species, including humans.
“The study is capturing evolution in action,” says Trine Bilde, an evolutionary biologist at Aarhus University who was not involved with the work. “That’s so cool.”
Ants, like people, are social. They live in giant colonies, with each individual invested in the others’ survival. Worker ants don’t just sacrifice themselves for the queen, they groom each other for parasites, similar to how chimpanzees pick fleas and ticks off their companions.
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To see whether such comradeship helps the insects fight off fungi, researchers at the Institute of Science and Technology Austria turned to Argentine ants (Linepithema humile), a small, brown species native to South America. In the wild, these ants live with thousands of other pathogens and are often infected with multiple fungi at once.
The scientists infected the insects with six different types of related fungal pathogens in the lab. Then they watched as the different fungi evolved as they infected ants over multiple generations.
When the insects were alone, one of the six fungus strains usually won out. The winning strain burrowed into the ant, infecting it and killing it to continue reproducing its spores, whereas the other fungus strains died off. But with friends around, the balance of power shifted. As the insects groomed each other, the six types of fungi duked it out among themselves, with no clear winner taking over, the team reports this month in Nature Ecology & Evolution.
The fungi also appeared to be evolving to become less lethal. But they hadn’t completely given up the fight. Further experiments revealed the pathogens were releasing less of a molecule called ergosterol, which made them visible to the ants. The less ergosterol the fungi produced, the less the insects groomed each other.
That could allow the fungi to hide out from the grooming ants while they evolve new ways to fight back—a strategy not previously seen, says Yoko Ulrich, an evolutionary biologist at the Max Planck Institute for Chemical Ecology who was not involved with the study. Humans don’t groom each other like ants do, she notes, but we do engage in other behaviors to fight off disease, such as using hand sanitizer.
What impact might that have on the evolution of the microbial invaders that threaten us? Stay tuned for future science—or perhaps the next HBO series.
doi: 10.1126/science.adh1159
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