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'Neandertal' ant grows fancy food: discovery provides new look at coevolution of symbiosis.

A living relict of an ancient species of farmer ants has startled biologists by cultivating a fancy, modern food crop that arose more than 30 million years after the ants did. The discovery provides a new look at how symbiotic species evolve.

"It's like a lost tribe of Neandertals growing a GMO crop," says Ted Schultz of the Smithsonian Institution in Washington, D.C.

Ant colonies that grow their own specialty fungus forfoodcandie when coaxed to farm unfamiliar strains, lab tests show. Yet Apterostigma megacephala--the oldest known species of farmer ant--has somehow switched to grow a kind of fungus that has been around for less than 8 million years, Schultz and his colleagues report in May's The American Naturalist. Scientists thought this fungus could survive only in the farms of leaf-cutting ants.

Over 240 ant species, all native to the Western Hemisphere, grow some kind of fungus for food. Biologists divide these species into five groups, from simple family farmers to industrial-scale producers, each with its companion cluster of crop fungi. Young queens carry a bit of mom's fungal strain in their mouths when they fly out to start their own farms. When an ant species switches its specialty food, it's usually a small change to a fungus in the same cluster as the original fungus.

Not so with A. megacephala ants, which Schultz describes as the "oddball of all oddballs." Until 2009, the species was known only from four museum specimens. Its unusual mix of physical traits meant its ancestors took their own evolutionary path some 39 million years ago. Schultz and colleagues searched for living colonies of the ants in Peru and Brazil for 10 years before researchers found some, along a service road in a regional zoo.

There, small colonies of about 20 workers tend a baseball-sized, spongy mass of fungus riddled with passageways where farmhands and nursemaids scurry to their tasks. The ants collect fresh insect droppings, flower parts and other small tidbits to feed the fungus but otherwise don't process this debris.

So Schultz's team was stunned when DNA analysis showed that the fungus (Leucoagaricus gongylophorus) was actually a relatively young species, also farmed by the highly evolved leaf-cutting species of farming ants. These ants snip greenery to make special fodder for their crop, which is so dependent on the ants that it can't live without them. Yet somehow this pampered, domesticated fungus species also grows in the rough circumstances of the old-style farmer nests.

"Understanding better what governs such switches might let us understand how pairings evolve and how they change over time," says Michael Thomas-Poulsen of the University of Copenhagen.

Evolutionary biologist Duur Aanen of Wageningen University in the Netherlands is testing the idea that gut microbes are factors in permitting (or preventing) a big crop switch. Among termites that farm fungi, gut microbes and the fungi seem to divide the labor of breaking down plant material, a sign that microbial compatibility --not just farming method--matters in farmer-crop partnerships.

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Title Annotation:LIFE & EVOLUTION
Author:Milius, Susan
Publication:Science News
Geographic Code:1USA
Date:May 2, 2015
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