Einstein Science Reporting for Kids
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4-Feb-2005

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On real ant farms, the crop is in control



A newly escavated underground fungus garden of A. octospinosus. Image courtesy of David Nash.
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On an ant farm, who is the farmer and what is being raised for food? At first, you might imagine a person as the farmer and the ants scurrying around their empty jar or fish tank as the farm animals. And then you might do a little research and learn that, in the wild, some ants run their own farms and raise all sorts of things, from aphids to tiny mushroom-relatives in the fungus family.

In a new study, Danish scientists looked even closer at leaf-cutter ants and the fungi they grow in their gardens and found that the fungi -- not the ant farmers -- are in charge of weed control.



Close-up of fungus garden of A. echinatoir. Image courtesy of David Nash,
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The leaf-cutter ants' fungus gardens grow underground, each roughly the size of a tennis ball. The ants fertilize the gardens with leaf bits and manure and then eat the fungi. When a young ant queen leaves home to start her own colony, she will take a bit of fungus with her to begin her own set of gardens.

All the fungi in one ant colony are clones from a single strain, meaning they have the very same genetic makeup.

They reproduce by making identical copies of themselves. It's possible that the ants might bring in outsider strains from another garden, but the new research shows that the fungi have special tricks for keeping out any competition.



An A. echinatoir queen on her colony fungus garden. Image courtesy of David Nash.
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Researchers Michael Poulsen and Jacobus Boomsma studied some of the different strains of fungi found in different ant colonies and found that the strains refused to grow together in the same space.

The researchers also studied the way that the ants fertilize the fungus gardens with their manure. Usually, the fungi absorb the tiny manure droplets, which help them grow. The researchers learned, however, that if the ants eat foreign fungus (and have traces of it in their manure), then the "resident" fungus won't absorb the manure.

"So what we think happens is the resident fungus reacts to foreign clones that have contaminated the garden, in order to make sure that the fungus protects its own interests," said Poulsen.

By making sure the ants only grow a single crop, the fungus can put all its energy into growing instead of competing with outsider strains. The researchers describe their findings in the 04 February issue of the journal Science.

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