Small Matters

Millions of years ago, leafcutter ants learned to grow fungi. But how? And why? And what do they have to teach us?

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Although thousands of ants from dozens of species are on the move through thick leaf litter, Schultz is fixated on a particular, solitary ant, which has clipped a piece of wild mushroom and is hauling the booty across a log, wobbling under its load. “Hey, you have to see this!” Schultz shouts to Mueller. It’s a Trachymyrmex, among the more derived, or “higher,” attines.


Schultz is excited. And surprised. Though he has read about attines carrying wild fungi into their nests, he’s never seen one actually do it. And why would they? The introduction of an incompatible fungus might well disrupt, or even destroy, the entire ant garden. What’s going on here?


“This is a puzzle,” Schultz says. “I would expect the ants to be very choosy about what they bring into the nest, to have some kind of sensory bias that accepts the ‘good’ fungi and rejects all the ‘bad’ ones.” Mueller notes that many plants use ants to disperse seeds, though whether the ants exercise choice about what they pick up, or only respond to the seduction of plant secretions, remains unclear.


Schultz is looking positively giddy, even though the ant and its fungus could turn upside down many of the things he and his colleagues have written, not to mention challenge most of their assumptions. “Maybe it’s not that the ant found the fungus,” Mueller suggests with a wry smile. “Maybe it’s that the fungus found the ant.”


Both Schultz and Mueller credit their fungi-obsessed collaborators for leading them to the idea that the fungi are profiting as much from the relationship with the ants as the ants are from the fungi. Carried by the ants, protected by them and tended in gigantic gardens, the fungal clones enjoy reproductive capacities far beyond what they could achieve untended. After all, free-living fungi often exist on just a tiny swatch of leaf litter, reproducing only once or twice before dying out. Inside the nests, the fungus becomes, in Stephen Rehner’s view, “immortal in comparison to any of their wild relatives.”


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