Cat parasite may alter Yellowstone wolf behavior

A parasite found in cat feces that alters animal behavior may be partly responsible for wolves deciding to become pack leaders or to disperse from their natal packs.

TWS member Connor Meyer, a PhD student at the University of Montana, remembers becoming interested in the parasite Toxoplasma gondii while an undergraduate freshman in 2012. He learned in one of his courses that mice contract the parasite and then start acting bolder, making them more likely to be killed by cats. “Knowing ‘toxo’ could infect any warm-blooded species—mammals and birds—stuck in the back of my head as something interesting to look at in the future,” he said.

Sure enough, after working on the Yellowstone Wolf Project and the Yellowstone Cougar project, Meyer had the opportunity to study the parasite in wolves (Canis lupus). Collaborating with colleagues and tapping into data collected on the population since their reintroduction into Yellowstone National Park in 1995, Meyer set out to find if toxoplasmosis may be correlated with changing wolf behavior. They published their findings in Nature.

“The literature of toxo shows that it increases risk-taking in infected individuals, whether it’s rodents, hyenas, chimpanzees, or any other species that toxo is studied in,” said Meyer, co-lead author of the study. “For us, we had 27 years of data.” That included blood serum samples they could test for toxoplasmosis antibodies as well as data on population densities and other demographics.

First, the team wanted to find out which wolf demographics were infected. After helicopter darting or net-gunning the wolves, the researchers recorded size and sex, and took their blood samples. They also noted whether the wolf came from the northern range of Yellowstone, where prey species like elk (Cervus canadensis) stay year-round, or the interior of Yellowstone, where elk migrate away from the snow and the wolves rely other food sources, including bison.

The northern range also has higher cougar (Puma concolor) densities. That’s important, Meyer said, because the parasite can only reproduce in felids. If there are more mountain lions in an area, they thought, wolves may be more likely to be infected with T. gondii.

Their research showed that was true. “Wolves that had higher overlap with cougars had a higher likelihood of becoming infected,” he said.

Meyer, Kira Cassidy, co-lead author on the study, and their colleagues believe that wolves are either finding infected cougar scat and consuming it, or it may be that the oocytes from the parasite are leaking into water supplies wolves are drinking from. Either way, they don’t seem to be getting the infection from infected elk prey.  The researchers tested more than 100 elk and none had the parasite.

The next step in their research was looking at infected wolf behavior. They classified risky behavior in wolves as becoming a pack leader; dispersal from the pack; approaching humans or vehicles; and being killed by other wolves or being killed by humans.

They found that wolves with toxoplasmosis were 46 times more likely to become a pack leader and 11 times more likely to disperse from their pack than uninfected wolves over the two-year period of the study. But Meyer stressed that toxoplasmosis isn’t the only reason wolves become pack leaders or disperse. “Toxo accelerates that process a little bit,” he said, adding that it may have something to do with the parasite increasing testosterone and dopamine in the infected animal.

They also don’t yet know whether those T. gondii-infected wolves are good leaders or have success after dispersal. The team also found no evidence of toxo-infected wolves being more likely to be killed by humans or another wolf.

Meyer said there’s still a lot to study about toxoplasmosis in wolves, but this adds another piece of the puzzle in understanding wolf ecology and natural history. Future research can help them learn if wolves positive for toxo, for example, may have more pups or higher survival. That could influence management decisions.

“There’s no evidence it’s decimating the wolf population or making super-predators,” Meyer said.