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A Strange Parasite Massively Improves A Wolf’s Chances Of Leading The Pack

Infection with the parasite makes the wolf over 46 times more likely to lead.

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Rachael Funnell

Digital Content Producer

clockNov 24 2022, 16:00 UTC
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toxoplasmosis wolves
Is a wolf's risk-taking behavior boldness, or parasitism? Image credit: Pat-s pictures / Shutterstock.com

There’s a parasite at work among packs of grey wolves in America’s Yellowstone National Park, and bizarrely, the animals it infects have a far greater chance of leading their pack compared to wolves who have swerved infection. The culprit? Toxoplasma gondii – the parasite responsible for toxoplasmosis, a disease we can pick up from infected feces and undercooked meat.

T. gondii is a strange parasite, having been associated with risk-taking behaviors in human hosts as well as animals. Research has linked infection with the parasite to certain political views, and even suggested it can make you more attractive to others. Now, a study has found it could have unexpected benefits for wolves with big ambition, too.

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The research looked at grey wolves (Canis lupus) living in Yellowstone, Wyoming, to see if or how infection with T. gondii influences wolf behavior. Armed with 26-years-worth of data and blood samples from 229 wolves, they were able to look for correlations between geography, behavior, and infection status.

Yellowstone is also home to cougars (Puma concolor) who are known to carry the parasite, and sure enough, wolves living in close proximity to pumas were more likely to be infected. Curiously, the analyses also showed that infection with the T. gondii parasite made the wolves much bolder.

toxoplasmosis wolves
Three sample packs with different cougar overlap categories and their corresponding predicted probabilities of T. gondii infection (negative in black; positive in red). Image credit: Kira Cassidy


Infected wolves were 11 times more likely to break away from the group compared to uninfected individuals. While dispersal is a natural part of wolf life, it’s a risky behavior because there is safety in numbers when moving with the pack.

Infected wolves were also more likely to become pack alphas. Each group is led by an alpha pair, and wolves infected with T. gondii are more than 46 times more likely to end up leading the pack in this way.

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As for why this association may exist, it’s possible that parasitism leading to risk-taking behaviors enables T. gondii to reach its ultimate goal: spreading as far and wide as possible.

“Due to the social hierarchy within a wolf pack, we hypothesize that the behavioural effects of toxoplasmosis may create a feedback loop that increases spatial overlap and disease transmission between wolves and cougars,” write the study authors.

“These findings demonstrate that parasites have important implications for intermediate hosts, beyond acute infections, through behavioural impacts. Particularly in a social species, these impacts can surge beyond individuals to affect groups, populations, and even ecosystem processes.”

Now, excuse us while we go contemplate the idea of a little T. gondii driving us around like Arquillian.

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The study was published in Communications Biology.


natureNaturenatureanimals
  • tag
  • animals,

  • animal behavior,

  • wolves,

  • parasites,

  • toxoplasma gondii

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