Climate change forced zombie ant fungi to adapt

May 29, 2018, Pennsylvania State University

Zombie ants clamp on to aerial vegetation and hang for months spewing the spores of their parasitic fungi, but researchers noticed that they do not always clamp on to the same part of the plant. Now the researchers know that the choice of leaves or twigs is related to climate and that climate change forced the fungi to adapt to local conditions.

"In tropical areas, zombie ants bite onto leaves, but in temperate areas, they bite twigs or bark," said David P. Hughes, associate professor of entomology and biology, Penn State.

Zombie ants are actually various species of carpenter ants that are infected with a parasitic fungus. About half the species of carpenter ants can be infected and each species has its own fungus. The zombie ant phenomena currently occurs around the globe on all continents except Europe. However, a fossil zombie ant was found in Germany, so they did once exist in Europe as well.

"They are probably not in Europe because the forests there are so managed," said Hughes. "They likely went locally extinct there."

Zombie ant spores fall on ants from above and the fungus multiplies in the ant body using it as a source of nutrition. Eventually, the fungus manipulates the ant to climb high into the branches and clamp on by biting. If an infected ant dies in the colony or on the ground it has zero chance of infecting another ant, so positioning the ant bodies where fungi can be widely distributed is essential for these fungi.

"In the late summer and early fall there are both leaves and twigs everywhere the ants reside," said Raquel G. Loreto, postdoctoral scholar in entomology, Penn State. "But in temperate areas the trees are deciduous and lose their leaves in the fall. There, the ants bite onto twigs."

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Article: Ant Zombie Tale: Mind-Controlling Fungus Loses to Lethal Foe

A fungus that invades the brains of ants, turning them into zombies on a death march, may have met its match. Another parasitic fungus, it turns out, effectively castrates the zombie-ant fungus so it can't spread its spores, a new study finds.

The finding explains how an ant colony can survive infestations by the zombie-ant fungus.

"In a case where biology is stranger than fiction, the parasite of the zombie-ant fungus is itself a fungus, a hyperparasitic fungus that specializes in attacking the parasite that turns the ants into zombies," said study leader David Hughes of Penn State University in a statement.

Continued:  http://www.livescience.com/20099-ant-zombie-mind-controlling-fungus.html

'Zombie ants' controlled by parasitic fungus for 48m years

The oldest evidence of a fungus that turns ants into zombies and makes them stagger to their death has been uncovered by scientists.

The gruesome hallmark of the fungus's handiwork was found on the leaves of plants that grew in Messel, near Darmstadt in Germany, 48m years ago.

The finding shows that parasitic fungi evolved the ability to control the creatures they infect in the distant past, even before the rise of the Himalayas.

The fungus, which is alive and well in forests today, latches on to carpenter ants as they cross the forest floor before returning to their nests high in the canopy.

The fungus grows inside the ants and releases chemicals that affect their behaviour. Some ants leave the colony and wander off to find fresh leaves on their own, while others fall from their tree-top havens on to leaves nearer the ground.

The final stage of the parasitic death sentence is the most macabre. In their last hours, infected ants move towards the underside of the leaf they are on and lock their mandibles in a "death grip" around the central vein, immobilising themselves and locking the fungus in position.

"This can happen en masse. You can find whole graveyards with 20 or 30 ants in a square metre. Each time, they are on leaves that are a particular height off the ground and they have bitten into the main vein before dying," said David Hughes at Harvard University.

The fungus cannot grow high up in the canopy or on the forest floor, but infected ants often die on leaves midway between the two, where the humidity and temperature suit the fungus. Once an ant has died, the fungus sprouts from its head and produces a pod of spores, which are fired at night on to the forest floor, where they can infect other ants.

Scientists led by Hughes noticed that ants infected with the fungus, Ophiocordyceps unilateralis, bit into leaves with so much force they left a lasting mark. The holes created by their mandibles either side of the leaf vein are bordered by scar tissue, producing an unmistakable dumb-bell shape.

Writing in the journal, Biology Letters, the team describes how they trawled a database of images that document leaf damage by insects, fungi and other organisms. They found one image of a 48m-year-old leaf from the Messel pit that showed the distinctive "death grip" markings of an infected ant. At the time, the Messel area was thick with subtropical forests.

"We now present it as the first example of behavioural manipulation and probably the only one which can be found. In most cases, this kind of control is spectacular but ephemeral and doesn't leave any permanent trace," Hughes said.

"The question now is, what are the triggers that push a parasite not just to kill its host, but to take over its brain and muscles and then kill it."

He added: "Of all the parasitic organisms, only a few have evolved this trick of manipulating their host's behaviour.

Why go to the bother? Why are there not more of them?"

Scientists are not clear how the fungus controls the ants it infects, but know that the parasite releases alkaloid chemicals into the insect as it consumes it from the inside.

• This article was amended on 18 August 2010. A phrase in the original said: "This can happen on mass." This has been corrected.

• On 21 December 2010 the picture was rotated 180 degrees after readers pointed out that it shows an ant gripping the underside of a leaf.