Tag Archives: zombie ant

3D image of an ant mandible adductor muscle (red) surrounded by a parasitic fungal cells (yellow). Credit: Hughes Laboratory/Penn State.

The fungus that turns ants into mindless zombies just got wickeder — controls host like a puppeteer

Nature can get disturbingly bizarre and scary. One of the most ghastly animal behaviors we know of is that of the ‘zombie ant fungus’ which takes control of living ants in order to spread its spores to other individuals. Scientists have studied by this disturbing strategy for more than a hundred years, and they’re still learning more about it. A new study found that the fungus is actually even sneakier than previously thought. Penn State researchers report that the parasite controls its hosts without actually infecting the brain. Instead, like a masterful puppeteer, the fungus takes control of the ant’s limbs, forcing the host to act against its own will. That’s just a whole new level of wickedness.

3D image of an ant mandible adductor muscle (red) surrounded by a parasitic fungal cells (yellow). Credit: Hughes Laboratory/Penn State.

Infected, zombified ant. Credit: Hughes Laboratory/Penn State.

The weird parasite, known as Ophiocordyceps unilateralis sensu lato, was first discovered by the British naturalist Alfred Russel Wallace in 1859, and is currently found predominantly in the tropical forests of Thailand but also Brazil’s rainforests. Once it infects a carpenter or worker ant, the parasite forces its host’s muscles to grab a leaf (or something else) when, where, and how the fungus wants it. They also force the ant to wander around in a drunken haze until it clamps its jaws on the underside of a leaf in what can only be called an ant zombie graveyard. The dead ant has now become food, helping the fungus to grow into a stalk out of the host’s head, which releases spores in the ground below where it should infect other ants. The cycle repeats and the fungus profits.

Previously, research showed that while holding on to the leaf with the death grip, the heads of diseased ants are filled with fungal cells and the muscles which operate the ant’s jaw are atrophied. Mandibles that normally open and close have now become unidirectional — they can only close. This keeps the ant from loosening its grip or dropping the leaf. Another thing the fungus does is suck all the calcium from the ant’s muscles, causing a condition similar to rigor mortis.

Penn State researchers have uncovered something different, though, after they painstakingly studied the corpses of infected ants in unprecedented detail. The scientists first infected ants with either the dreaded mind-control fungus or some other benign fungus in order to assess the cellular interactions unique to Ophiocordyceps u. 

“The fungus is known to secrete tissue-specific metabolites and cause changes in host gene expression as well as atrophy in the mandible muscles of its ant host. The altered host behavior is an extended phenotype of the microbial parasite’s genes being expressed through the body of its host. But it’s unknown how the fungus coordinates these effects to manipulate the host’s behavior,” said Penn State’s Maridel Fredericksen, lead author of the study.

Each infected ant was cut into numerous 50-nanometer slices of tissue which were imaged with scanning electron microscopy, then stacked to create a high-res 3-D image. A sophisticated machine learning algorithm then analyzed the slices to quickly and accurately identified fungal cells among ant cells.

parasitic ant fungal cells

3D image of an ant mandible adductor muscle (red) surrounded by parasitic fungal cells (yellow). Credit: Hughes Laboratory/Penn State.

Surprisingly, the analysis showed that while the fungal cells were spread throughout the ant’s body (head, thorax, abdomen, and legs), these were absent from the brain. However, fungal cells did cluster around the outskirts of the brain with which it interacted chemically, as reported in the Proceedings of the National Academy of Sciences.

“Normally in animals, behavior is controlled by the brain sending signals to the muscles, but our results suggest that the parasite is controlling host behavior peripherally,” says David Hughes, senior author of the study. “Almost like a puppeteer pulls the strings to make a marionette move, the fungus controls the ant’s muscles to manipulate the host’s legs and mandibles.”

This way, the researchers say, the fungus can take control of the ant while still keeping it alive — or at least until it’s served its purpose.

“We hypothesize that the fungus may be preserving the brain so the host can survive until it performs its final biting behavior – that critical moment for fungal reproduction,” says Hughes. “But we need to conduct additional research to determine the brain’s role and how much control the fungus exercises over it.”

Zombie ant fungi ‘know’ brains of their hosts

A while ago, we were telling you about the infamous “zombie ant fungus” – a parasitic fungus that reproduces by manipulating the behavior of ants. It’s one of the most gruesome acts in nature – the parasite fungi infect tropical ants, literally taking control of their actions, ultimately leading the infected ant to march to its death at a mass grave near the ant colony, where the fungus spores erupt out of the ant’s head so it can spread even further, infecting more ants. Now, a new study has shown that the fungus knows how to differentiate between ant species, emitting mind controlling chemicals only when it infects its natural target host.

Zombified ant – image via Wired.

The finding suggests that the fungus “knows” its target, offering more light into this rather poorly understood phenomenon.

“Fungi are well known for their ability to secrete chemicals that affect their environment,” noted lead author Charissa de Bekker, a Marie Curie Fellow in Penn State’s College of Agricultural Sciences, and Ludwig Maximilian of the University of Munich. “So we wanted to know what chemicals are employed to control so precisely the behavior of ants.”

The Ophiocordyceps fungus infects many species of fungus, so it’s quite curious that it only exerts its mind controlling abilities on one of them; even though it infects and kills other species as well, it can’t influence their behavior.

“The brain of the target species was the key to understanding manipulation,” de Bekker said.

In order to figure out how this works, they removed ant brains and artificially kept them alive in the lab, exposing them to the fungus.

“This was ‘brain-in-a-jar’ science at its best,” said co-author David Hughes, assistant professor of entomology and biology, Penn State. “It was necessary to reduce the complexity associated with the whole, living ant, and just ask what chemicals the fungus produces when it encounters the ant brain.

“You don’t get to see a lot of behavior with fungi,” he said. “You have to infer what they are doing by examining how they grow, where they grow and most important, what chemicals they secrete.”

While analyzing this interaction, the team found thousands of unique chemicals, most of them completely unknown to science.

“There is no single compound that is produced that results in the exquisite control of ant behavior we observe,” de Bekker said. “Rather, it is a mixture of different chemicals that we assume act in synergy.

“But whatever the precise blend and tempo of chemical secretion,” she said, “it is impressive that these fungi seem to ‘know’ when they are beside the brain of their regular host and behave accordingly.”

Though remarkable, the finding isn’t surprising – such a complex, behavior altering mechanism was bound to have a complicated underlying mechanism. Hughes notes:

 “This is one of the most complex examples of parasites controlling animal behavior because it is a microbe controlling an animal — the one without the brain controls the one with the brain. By employing metabolomics and controlled laboratory infections, we can now begin to understand how the fungi pull off this impressive trick.”

Furthermore, they also found that this phenomenon isn’t restricted to the tropical areas, as initially proposed – it also happens in North America.

Journal Reference: Charissa de Bekker, Lauren Quevillon, Philip B Smith, Kim Fleming, Debashis Ghosh, Andrew D Patterson and David P Hughes. Species-specific ant brain manipulation by a specialized fungal parasite. BMC Evolutionary Biology 2014, 14:166  doi:10.1186/s12862-014-0166-3

Zombie-ant fungus infection

Hyper-parasite defends ant colonies from zombie-ant fungus

Last year, we reported on one of the most gruesome and horrific acts that goes on in nature; it seems so unreal, like if some sort of SciFi monstrous scenario transcended into the realm of reality, that one has a hard time wrapping his head around it. Yes, as some of you might have read previously, I’m talking about the zombie-ant fungus or Ophio­cordy­ceps. These parasite fungi infect tropical ants, literary taking control of their actions, ultimately leading the infected ant to march to its death at a mass grave near the ant colony, where the fungus spores erupt out of the ant’s head so it can spread even further.

Zombie-ant fungus infection Now, scientists at Penn State University who have been studying interactions between the zombie-fungus and their host ants have found that there’s a third player at work. Coming to the rescue of the tropical ants, it seems, is another fungi – a parasite of parasite, typically referred to as an hyper-parasite. So, the counter-par­a­sites keep the first one in check and help pre­vent it from over­run­ning en­tire ant col­o­nies.

“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,” Hughes said. The research will be published in the journal PLoS ONE.

“The hyperparasitic fungus effectively castrates the zombie-ant fungus so it cannot spread its spores,” said Hughes, who is an assistant professor of entomology and biology, and a member of the Center for Infectious Disease Dynamics at Penn State. “Because the hyperparasitic fungi prevents the infected zombie-ant fungus from spreading spores, fewer of the ants will become zombies.”

The team of biologists, lead by Hughes, created a detailed model which offered extra insights regarding the fungus-infected ants and the parasite-infected zombie-ant fungus interaction. Previously, scientists had known that ants ward off infections by carefully grooming each other, now the model reveals the effect of ant behavior on limiting infection. Nature often sends in unexpected allies to aid those threatened by atypical enemies.

“Interest­ingly, be­yond the well-known ef­fect of de­fen­sive ant be­hav­ior, our new re­search re­veals the added ef­fect of the cas­trat­ing ac­tions of the hyperpar­a­site fun­gi, which may re­sult in sig­nif­i­cantly lim­it­ing the spread of the zom­bie-ant fun­gus,” Hughes said.

The sci­en­tists re­port that only about 6.5 per­cent of the spore-producing or­gans of the zom­bie-ant fun­gus were vi­a­ble.

“Even though there are a lot of dead and in­fected zom­bie ants in the neigh­bor­hood, only a few of the spores of the zom­bie-ant fun­gus will be­come ma­ture and able to in­fect healthy ants,” Hughes said. “Our re­search in­di­cates that the dan­ger to the ant col­o­ny is much smaller than the high dens­ity of zom­bie-ant ca­dav­ers in the gra­veyard might sug­gest. This com­plex in­ter­ac­tion be­tween ant col­o­nies, their brain-mani­pu­lat­ing par­a­sites, and oth­er fun­gi capa­ble of lend­ing as­sis­tance to the col­o­ny un­der­scores the need to study so­cial in­sects un­der nat­u­ral con­di­tions.”

The findings were reported in the journal PLoS ONE.

source: Penn State University

Of Zombie ants, fungus and mind control

New amazing yet gruelsome details have emerged, regarding how a fungus can control an unfortunate ant. Basically, the fungus infects the ant’s brain, and then tells it what to do, in a somewhat similar fashion to what a Goa’uld would do.

Zombies in Thailand

Venturing deep in the Thai forest, researchers have found a species of fungi, Ophiocordyceps, which spreads its cells into the ant’s brain, thus forcing its muscles to grab a leaf (or something else) when, where and how the fungus wants it. They also force the ant to wanter around in a drunken fashion until it clamps its jaws on the underside of a leaf in what can only be called an ant zombie graveyard.

By studying 16 infected ants, researchers concluded that their last bites take place around noon, indicating they are synchronized with a sun-related cue, such as temperature or humidity.

“Synchronized arrival of zombie ants at the graveyards is a remarkable phenomenon. It adds a layer of complexity on what is already an impressive feat,” wrote David Hughes, a study researcher from Pennsylvania State University, in an email to LiveScience. “However, although ants bite at noon they don’t in fact die until sunset. Likely this strategy ensures (the fungus) has a long cool night ahead of it during which time it can literally burst out of the ant’s head to begin the growth of the spore-releasing stalk”.

Unfortunate ants

It is indeed an awful fate for the ants, who usually live in the canopies of trees, but occasionally come to the ground, where they contact the fungus. Scientists observed a total of 42 infected ants, which unlike healthy ones who walk in zig zag trails, wander around aimlessly, until they finally take their last bite. They dissected a few, and found that while holding on to the leaf with the death grip, their heads are filled with fungal cells and the muscles which operate the ant’s jaw were atrophied.

“In the context of biting, it allows the mandibles, we feel, to work in one direction and one direction only,” Hughes said. “Normally, they open and close, but in this case they can only close.”

This keeps the ant from loosening its grip or dropping the leaf. Another thing the fungus does is suck all the calcium from the ant’s muscles, causing a condition similar to rigor mortis. It’s not the only time researchers have seen fungus behave in this mind controlling way; they have also seen fungus manipulating arthropodes, crickets, bees, wasps, and even spiders.

“We are quite confident we could see this and similar phenomenon across a broad range of organisms, because it is such a neat evolutionary trick if you are fungus to use the muscles of an animal to transport you to another environment,” he wrote. (Many fungi rely on wind or other means to passively disperse their spores.)

All in all, it’s an extremely unfortunate fate for the ants, but a valuable source of information for researchers, who are just starting to learn about this sort of interaction.