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 interesting 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 Communications Biology.

The researchers analyzed behavioral and distribution data from 1995 to 2020, as well as blood samples from 229 anesthetized wolves, to study the link between risky behavior and Toxoplasma gondii infection. They identified associations between parasite infection and high-risk behavior in both men and women.

PHOTO: Members of the Junction Butte Wolf pack walk past a trail camera in Yellowstone National Park on March 12, 2019.

Members of the Junction Butte Wolf pack walk past a trail camera in Yellowstone National Park on March 12, 2019.

The Yellowstone Cougar Project

Wolves that tested positive for T. gondii were found to be 11 times more likely to disperse from their pack and more than 46 times more likely to become a pack leader than uninfected wolves. Males were 50% more likely to leave their pack within six months if infected with the parasite, but this time jumped to 21 months if they were unaffected. 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 scientists say it can be fatal for young or immunosuppressed wolves. According to Connor Meyer, Ph.D. in wildlife biology, they don’t yet know how this parasite affects things like survival rates. student at the University of Montana and one of the study’s authors.

The findings are the first to demonstrate parasite infection influencing decision-making and behavior in this species, the researchers said.

Previous research has identified links between T. gondii infection and increased boldness in hyenas, as well as increased testosterone production in rats. The authors speculate that similar mechanisms could drive the risk-taking behavior observed in wolves that tested positive for the parasite.

Wolves inhabiting areas that overlapped with higher cougar population densities were more likely to be infected with T. gondii than those that did not live near cougar, suggesting that wolves may become infected with the parasite through direct contact with cougars and their environment. , the researchers found. Cougars in Yellowstone National Park are known to host the parasite.

PHOTO: Alpha male wolf from the Canyon Pack in Yellowstone National Park, November 25, 2019.

An alpha male wolf from the Canyon Pack in Yellowstone National Park, November 25, 2019.

Neal Herbert/NPS

The findings “tell the story of this whole ecosystem and how species interact with each other,” said Kira Cassidy, one of the authors and a researcher for Yellowstone National Park and Yellowstone Forever, a nonprofit organization affiliated with the national park.

The researchers hypothesized that the infection would have a wider impact on the wolf population, as infected pack leaders could introduce 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 the connection to the actual mechanism behind the parasite and the infection,” Meyer said.

PHOTO: Nine wolves interact on the crisp snow in Yellowstone National Park on November 21, 2019.

Nine wolves interact on the crisp snow in Yellowstone National Park on November 21, 2019.

Doug Smith/NPS

The study, only the second of its kind to look at how toxoplasmosis infection can affect a predator species, is “a powerful kind of testament to what long-term research can answer,” Meyer noted.

Cassidy added, “Taking 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 widely extirpated in the western US in the 1940s, but populations have begun to recover in recent decades. Some say the increase is harmful to humans because of wolves’ ability to travel vast distances and therefore spread disease. Wolves can also be a significant factor in the decline of big game herds and the killing of livestock.

Earlier this month, a federal judge in Montana temporarily restricted the hunting and trapping of wolves near Yellowstone and Glacier National Parks.

PHOTO: Detail of the face of a gray wolf in Yellowstone National Park on November 7, 2017.

A close-up of the face of a gray wolf in Yellowstone National Park on November 7, 2017.

Jacob W. Frank/NPS

However, wolves are usually wary of humans. In Yellowstone, they are the “shyest and most cautious” of all large mammals, Cassidy said.

“If you see one, you’re incredibly lucky,” she said. “Overall, I’d say they’re basically not a danger to humans.”

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