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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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The scientists’ penchant for likening ant fungiculture to human agriculture has drawn critics. Naomi Pierce, a Harvard specialist in ant/plant interactions, praises their fieldwork, but thinks that turning ants into farmers may be carrying things too far. “The trouble is that you can get trapped by the metaphor,” she says. Ants, of course, did not consciously develop agriculture. Projecting human intention onto ants, says Ignacio Chapela, may blind researchers to the reasons why ants do what they do.

 

While Mueller and Schultz worked on the ants’ relationship to fungi, a team of biologists at the University of Toronto were noting—and wondering about—the presence of a persistent and ravaging mold, called Escovopsis, in attine gardens. How was it, they asked, that this potent parasite didn’t regularly overrun the attine nests? Taking note of a white powder on the undersides of the attine ants, they ultimately identified it as a type of bacteria, Streptomyces, that secretes antibiotics. The antibiotics were keeping the Escovopsis at bay. More important, they were doing so over long periods of time, without the Escovopsis becoming totally resistant.

 

There may be a kind of “staged arms race,” says Cameron Currie, one of the Toronto researchers (now at the University of Kansas), in which the attine antibiotics continually adapt to any resistance built up in the Escovopsis. The parasite isn’t wiped out entirely, but neither does it swamp the nest. Currie is now trying to determine how long this chemical cross fire has been taking place.

 

A textbook case of symbiosis between the ants and fungi suddenly was shown to have four major players—or five, if you count the antibiotics produced by the bacteria. When these antibiotics don’t do the trick, the ants chop out infected chunks of fungus and drag them far from the nest.

 

In the rain forest, dawn has yet to break; nocturnal Blepharidatta ants, close relatives of the attines, are still at work, hauling minuscule grains of cereal, which Mueller spread around the night before. The bait has let Mueller track the Blepharidatta to their nest. Because Blepharidatta, which do not grow fungus, have been observed carrying around bits of free-living fungus, Mueller suspects they may be on the verge of cultivation themselves. Mueller is particularly intrigued by experiments in which Blepharidatta move clumps of fungus closer to their nests. “We’re looking for something very deep in the evolutionary past,” Mueller says. “Some ant in these forests started to associate with the fungus. And that transition is the same transition that human beings made.”

 

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