Thursday, March 3, 2011

4 New Species of Zombifying Fungus Found

(Because I take my charge to bring you the latest in funky insect news very seriously, my newest piece from 

Four new species of brain-manipulating fungi that turn ants into "zombies" have been discovered in the Brazilian rain forest.
These fungi control ant behavior with mind-altering chemicals, then kill them. They're part of a large family of fungi that create chemicals that mess with animal nervous systems.

Usually scientists study these fungi as specimens preserved in a lab, said entomologist David Hughes of Pennsylvania State University, co-author of a study March 3 PLoS ONE. "By going into the forest to watch them, we found new micro-structures and behaviors."

Once infected by spores, the worker ants, normally dedicated to serving the colony, leave the nest, find a small shrub and start climbing. The fungi directs all ants to the same kind of leaf: about 25 centimeters above the ground and at a precise angle to the sun (though the favored angle varies between fungi). How the fungi do this is a mystery.

"It's related to the fungus that LSD comes from," Hughes said. "Obviously they are producing lots of interesting chemicals."

Before dying, ants anchor themselves to the leaf, clamping their jaws on the edge or a vein on the underside. The fungi then takes over, turning the ant's body into a spore-producing factory. It lives off the ant carcass, using it as a platform to launch spores, for up to a year.

"This is completely different from what we see in temperate zones where, if an insect dies from a fungal infection, the game's over in a few days," Hughes said.

"The fungi rots the body of the insect and releases massive amounts of spores over two or three days. But in the tropics, where humidity and temperature are more stable, the fungi has this strategy for long-term release."

Of the four new species, two grow long, arrow-like spores which eject like missiles from the fungus, seeking to land on a passing ant. The other fungi propel shorter spores, which change shape in mid-air to become like boomerangs and land nearby. If these fail to land on an ant, the spores sprout stalks that can snag ants walking over them. Upon infecting the new ant, the cycle starts again.

Chemicals from this global group of fungi, known as Cordyceps, have been a part of traditional medicine for thousands years, and part of Western medicine for the last 50.

Organ transplant patients, for example, receive ciclosporin — a drug that suppresses the immune system, reducing the chance the body will reject the new tissue. Chemicals from this same fungal group are also used for antibiotic, antimalarial and anticancer drugs.

The fungi help the forest by keeping ant populations in check. "All of the problems with global ant infestations, for example the Argentine fire ant," Hughes said, "is because the ants have escaped their natural enemies. Then they become a pest."

These fungi need a precise level of humidity to survive. As global temperature changes, the forests where they live are drying. Hughes and his colleagues are now studying the decline these fungi.

"We're worried we'll see the extinction of a species we've only just managed to describe."

On the following pages are more photographs of zombifying fungi in action.
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All images: David Hughes, Pennsylvania State University

See Also:

Citation: “Hidden diversity behind the Zombie-Ant fungus Ophiocordyceps unilateralis: Four new species described from Carpenter ants in Minas Gerais, Brazil.” By Harry C. Evans, Simon L. Elliot, David P. Hughes. PloS One, Vol. 6 No. 3, March 2011.

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