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.

According to a study published Thursday in Communications Biology.

The researchers analyzed behavioral and distribution data from 1995 to 2020 along with blood samples from 229 anesthetized wolves to investigate the association between risky behaviors and Toxoplasma gondii infection. They identified associations between parasite infection and high-risk behaviors in both men and women.

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

Yellowstone Cougar Project

Wolves testing positive for T. gondii were 11 times more likely to disperse from their pack and more than 46 times more likely to become a pack leader than uninfected wolves, according to the results. Males were 50% more likely to leave their pack within six months if infected with the parasite, but this increased to 21 months if unaffected. Females showed a 25% chance of leaving their pack within 30 months if infected, extending up to 48 months if uninfected.

According to the researchers, infection with T. gondii often has no negative effect on the body condition of healthy individuals, but can be fatal in young or immunocompromised wolves. They don’t yet know how this parasite influences things like survival rates, according to Connor Meyer, a PhD in wildlife biology. student at the University of Montana and one of the authors of the study.

The results are the first to demonstrate parasitic infection affecting decision-making and behavior in the species, the researchers said.

Previous research has identified associations 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 risky behaviors seen in hyenas. wolves tested positive for the parasite.

Wolves occupying areas that overlapped with a higher population density of cougars were more likely to be infected with T. gondii than those that did not live near cougars, suggesting that wolves can become infected with the parasite at following direct contact with cougars and their environments. , the researchers found. Cougars in Yellowstone National Park are known to be hosts for the parasite.

PHOTO: Canyon Pack alpha male wolf in Yellowstone National Park, November 25, 2019.

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

Neal Herbert/NPS

The results “tell the story of this whole ecosystem and how the species interact with each other,” said Kira Cassidy, one of the authors and research associate for Yellowstone National Park and Yellowstone Forever, an organization at non-profit organization associated with the national park.

The researchers speculated that the infection would have wider implications for the wolf population, as infected pack leaders could lead their packs into higher-risk areas that overlap cougars, potentially increasing the risk of additional infection for uninfected wolves.

“So that’s probably the link to the actual mechanism behind the parasite and the infection,” Meyer said.

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

Nine wolves interact atop crispy snow in Yellowstone National Park on November 21, 2019.

Doug Smith/NPS

The study, only the second of its kind to examine how toxoplasmosis infection can affect a species of predators, is “kind of powerful testimony to what long-term research is capable of answering,” Meyer noted.

Cassidy added, “Taking an ecosystem approach to a research question can be very difficult in many 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 from the western United States in the 1940s, but populations have started to rebound in recent decades. Some say that the increase is detrimental to humans due to the ability of wolves to travel great distances and therefore spread disease. Wolves can also be a significant factor in the decline of big game herds and the culling of livestock.

Earlier this month, a federal judge in Montana temporarily wolf hunting and trapping restricted nearby Yellowstone and Glacier National Parks.

PHOTO: A close-up of a gray wolf's face 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

Wolves, however, are generally cautious around people. 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. “I would say that overall they pose essentially no danger to people.”

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