When a common parasite infects wolves, it changes their behavior and turns them into high-risk animals that can help them become leaders of their pack — or get them killed. That’s according to a new study published Thursday in the journal Communication Biology found that a wolf infected by Toxoplasma gondiia unicellular parasite that invades warm-blooded animals was more than 46 times more likely to take over leadership of its pack than an uninfected wolf, thanks to the parasite’s ability to induce more risky behavior.
“We focus so much on the dynamics of vertebrates — wolves and moose, and how they affect each other — and for a long time it seems like we’ve generally ignored the fact that parasites can play a role in those relationships,” Connor Meyer , an ecology researcher at the University of Montana and the lead author of the new study, told The Daily Beast. “With something like Toxoseems like we should give parasites a little more credit.
Host behavior modification — the buttoned-up, scientific way of saying “mind control” — is a common but devious tactic that infectious diseases have developed over time. Just look at “zombie ants,” which either describe ants infected with a fungus that takes over their brains; or a parasitic worm that causes ants to walk on blades of grass and lock their jaws, increasing the chances of a cow eating them. Elsewhere in nature, parasitic worms can also zombify snails and cause their eye-stalks to take on the appearance of maggots, which predatory birds find attractive.
Behavioral change that causes a host to be eaten by a predator usually means that the underlying parasite infects multiple host species as part of its full life cycle, and the same goes for Toxoplasma. The parasite can infect many different animal species, including humans. Therefore, pregnant women are advised not to scoop out the cat litter. Some research suggests that toxoplasmosis could change our behavior by causing hormones such as dopamine and testosterone to increase, but the only known host that makes it possible to reproduce sexually is the cat family to which domestic cats belong – which means having of a cat increases the chances that you might have it Toxoplasma swimming around in your body. And once the parasite is there, it can stick around for a lifetime, although people rarely show symptoms after the acute phase of infection.
But the spikes in dopamine and testosterone caused by Toxoplasma are especially important to watch out for in other intermediate host species, as they can cause a phenomenon that scientists truly call “fatal attraction.” Toxoplasma-infected animals such as rats and hyenas become bolder around felines, increasing the likelihood of them being eaten and allowing the parasite to reproduce.
In other words, it appears that the parasite is trying to place its intermediate host in more dangerous positions where it is likely to be snatched away by a potential true host.
In Yellowstone National Park, it was a mystery how Toxoplasma spread to wolves because they must ingest a form of the parasite called an oocyst to become infected. That is, until Meyer made the connection that one type of big cat roams the park: cougars. He and his co-authors believe that one aspect of wolves’ relationship with these cougars is much like a dog’s family relationship with a cat.
“Some dogs really like to raid the litter box if you don’t get to it fast enough,” he said. “We would expect wolves to be very similar, when they come across cougar feces in the landscape, they could very well eat it and become infected that way.”
For the study, Meyer and his team tested blood samples from 62 different mountain lions and 229 wolves that lived in Yellowstone between 1995 and 2020.
Wolves’ infection status was also mapped alongside their observed behaviors, such as leading a pack or leaving the pack.
That’s what the team found Toxoplasma-infected wolves were more likely to become leaders of their pack and, on average, left the pack earlier than uninfected wolves — an apparent contradiction that could be interpreted as the parasite increasing risk-taking and aggressive behavior across the board, Meyer said.
But host behavior modification isn’t all bad. There’s an important benefit to the wolves in becoming pack leaders: “Leaders become breeders” is the adage when it comes to the dominant male and female in a pack, Meyer said. While the wolves most likely can’t pass the parasite on to their offspring, they can teach the pack to engage in riskier behaviors and spend more time around cougars, helping other members pick up the infection.
Investigating this crazy example of mind control could have lasting implications when it comes to monitoring the careful balance of Yellowstone’s ecosystem. The reintroduction of wolves to the park is “one of the greatest conservation success stories in North America,” Meyer said, and understanding the behavior of infected wolves could help further preserve the animals. A tiny parasite that can affect an entire ecosystem – that’s proof that size doesn’t matter.