Alberta researchers investigate how zombie parasites take control of ant brains
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parasites → investigate → brains
Dicrocoelium is one of the best examples of parasitic mind control, say local researchers
In the southeast corner of Alberta, the Cypress Hills are a dramatic sight rising out of a sea of prairie.
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Hills → say → prairie
Look down, and you’ll see another drama playing out.
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drama → look → ?
Ants are clasped onto plants and shrubs throughout the Cypress Hills Provincial Park against their will, waiting to be accidentally swallowed up by an unsuspecting herbivore.
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Ants → clasp → herbivore
The culprit is the parasite Dicrocoelium dendriticum, a worm with an incredible ability to zombify its host.
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culprit → zombify → host
According to researchers at the University of Calgary and University of Lethbridge, this parasite sits alone in the hall of fame of parasite manipulations because it is able to turn its control on and off — something not seen elsewhere in the world of zombies.
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it → accord → zombies
Zombie parasites are quite common in nature, says Cameron Goater, a parasitologist and professor emeritus at the University of Lethbridge.
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Goater → say → Lethbridge
“Almost every taxon [species] of hosts on the tree of life contains parasites or are infected with parasites that lead to manipulation,” said Goater.
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Goater → contain → manipulation
The goal is often to get from one host to the next.
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goal → get → next
Infected ants climb plants and die so that the fungus can burst out and rain spores down on unsuspecting ants.
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fungus → climb → ants
Or the horsehair worm that drives crickets to commit suicide by jumping into water so the worms can emerge and mate.
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worms → drive → water
These examples and nearly all others in the animal kingdom end in the host's death, but Dicrocoelium is different because the nature of its life cycle incentivizes keeping the host alive.
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nature → end → host
Dicrocoelium has what parasitologists call a complex life cycle involving multiple hosts.
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parasitologists → have → hosts
The final host is a grazing mammal like elk, deer or cattle.
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host → graze → elk
Adult worms live in their livers, and their eggs are pooped out and eaten by snails.
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eggs → live → snails
In snails, the egg divides into hundreds of larval forms called cercaria.
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egg → divide → forms
These are packaged in mucus and coughed out as a slime ball.
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These → package → ball
Slime balls are then eaten by ants, and all but one cercaria go to the abdomen, while a single "brainworm" cozies up next to the ant's brain.
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brainworm → eat → brain
This is where the challenge begins.
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challenge → begin → ?
“The problem is the final host almost never ingests ants,” said Goater.
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Goater → ingest → ants
“In many cases, things like deer and elk and cattle actually avoid ants.
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things → avoid → ants
So, it helps to have a brainworm that compels the ants to climb plants where they can be accidentally eaten.
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they → help → plants
Ants clinging to vegetation are exposed to predators, they can’t eat and, importantly, they are extremely susceptible to dehydration.
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they → cling → dehydration
“The solution to that problem is to detach from a plant and go back to the nest,” said Goater.
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Goater → detach → nest
“That's where this on-off switch comes from.”
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switch → come → where
For the rest of their lives, these ants climb plants and cling on so long as the temperature is below approximately 19 C.
How can a parasite inside an ant know what temperature it is outside and adjust its mind control in response?
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it → climb → response
“That's exactly the kind of question that keeps us awake at night,” said Goater, “because it seems that the mechanisms that run that might be something completely new.
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that → keep → night
How to take over a mind
The first step to understanding this phenomenon is to look at the genes being expressed during and after the clinging behaviour, and comparing this with uninfected ants.
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step → take → ants
“We've gone inside the brain of the ant to try and determine what those changes are from the ant perspective,” said James Wasmuth, a parasitologist at the University of Calgary.
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Wasmuth → go → Calgary
“And we see a lot of changes in different biochemical pathways when it's doing the zombie behaviour.
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it → see → behaviour
”
While it appears the ant is not sensing the environment in a normal way when it’s under parasite control, it is difficult to pinpoint one change that is driving behaviour, said Wasmuth.
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Wasmuth → appear → behaviour
According to Shelley Adamo, an insect neurobiologist and professor emeritus at Dalhousie University, this is to be expected.
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this → accord → University
“When I first got into this business, the assumption everyone had was there was a magic bullet,” said Adamo.
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Adamo → get → business
However, the more scientists learn about these systems, they realize that’s not the case.
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that → learn → systems
“Evolution rarely does the grand redo,” Adamo said.
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Adamo → do → redo
Parasites like Dicrocoelium work by tapping into existing systems, which are themselves extremely complex.
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which → work → systems
“We rely on chemicals for communication from one nerve cell to another; it's not hardwired,” Adamo said.
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Adamo → rely → another
This gives the parasite ample opportunity to interfere, gradually evolving ways to nudge these systems to their benefit.
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This → give → benefit
The result is a plethora of subtle changes culminating in the precise manipulation.
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result → culminate → manipulation
Solving that puzzle requires many careful experiments where some genes are suppressed or not to see if the manipulation remains.
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manipulation → solve → experiments
…and 19 more, not listed.
The Aporia
