Gray wolves infected with this parasite are more likely to become pack leaders, scientists say
Researchers studying gray wolf populations in Yellowstone National Park have discovered an intriguing reason why some wolves may be more inclined to become pack leaders.
Gray wolves exposed to Toxoplasma gondii — the parasite that causes the disease toxoplasmosis — are more than 46 times more likely to become pack leaders than uninfected wolves, according to a study published Thursday in Communication biology.
Researchers analyzed behavioral and distribution data from 1995 to 2020 as well as blood samples from 229 anesthetized wolves to study the association between risky behavior and Toxoplasma gondii infection. They identified an association between parasite infection and high-risk behavior in both men and women.
Wolves that tested positive for T. gondii were 11 times more likely to disperse from their pack and more than 46 times more likely to become pack leaders than uninfected wolves, according to the findings. Males were 50% more likely to leave their pack within six months if infected with the parasite, but that time jumped to 21 months if uninfected. Females showed a 25% chance of leaving their pack within 30 months if infected, extending to 48 months if uninfected.
Infection with T. gondii often has no negative effects on the condition of healthy individuals, but it can be fatal for young or immunocompromised wolves, according to the researchers. They don’t yet know how this parasite affects things like survival rates, according to Connor Meyer, a wildlife biology Ph.D. student at the University of Montana and one of the authors of the study.
The findings are the first to show that parasite infection affects decision-making and behavior in a species, the researchers said.
Previous research has identified a link between T. gondii infection and increased boldness in hyenas, as well as increased testosterone production in rats, the authors speculate that similar mechanisms may drive the risky behaviors observed in wolves that tested positive for the parasite.
Wolves living in areas that overlap with higher cougar population densities were more likely to be infected with T. gondii than those not living near cougars, suggesting that wolves may become infected with the parasite as a result of direct contact with cougars and their environment. the researchers found. Cougars in Yellowstone National Park are known to host parasites.
The findings “tell a story about this whole ecosystem and how species interact with each other,” said Kira Cassidy, one of the authors and a research associate at Yellowstone National Park and the national park-affiliated nonprofit Yellowstone Forever.
The researchers hypothesized that infection would have broader implications for wolf populations, as infected pack leaders could lead their packs into more at-risk areas that overlap with cougars, potentially increasing the risk of further infection for uninfected wolves.
“So that’s probably a link to the actual mechanism behind the parasite and the infection,” Meyer said.
The study, only the second of its kind to look at how toxoplasmosis infection can affect a predator species, “is a powerful kind of testimony to what long-term research can answer,” Meyer noted.
Added Cassidy, “An ecosystem approach to a research question can be really difficult in a lot of places, but Yellowstone is one of those places where we see all the species that were here hundreds of years ago.”
Gray wolves were largely eradicated in the western United States in the 1940s, but populations have begun to recover in recent decades. Some say increase is harmful to humans due to wolves’ ability to travel long distances and therefore spread disease. Wolves can also be a significant factor in reducing large game herds and killing livestock.
Earlier this month, a federal judge in Montana temporarily limited wolf hunting and trapping nearby Yellowstone and Glacier National Parks.
However, wolves are usually wary of humans. In Yellowstone, they are the “shyest and most wary” of all large mammals, Cassidy said.
“If you see him, you’re incredibly lucky,” she said. “I’d say they’re generally not dangerous to humans.”