A Strange Thing Happens To Wolves Infected With An Infamous Mind-Altering Parasite

A study of 26 years of wolf behavior data and blood analysis of 229 wolves showed that infection with the parasite Toxoplasma gondii makes wolves 46 times more likely to become a pack leader.

Research shows that the effects of this parasite in nature have been woefully understudied – and its role in ecosystems and animal behavior underestimated.

If you have a cat, you’ve probably heard of this parasite. The microscopic organism can only reproduce in the body of felines, but it can infect and thrive on virtually any warm-blooded animal.

This includes humans, where it can cause a usually asymptomatic (but still life-threatening) parasitic disease called toxoplasmosis.

Once it is in another host, nobody T. gondii parasites must find a way to bring their offspring back inside a cat or it will become an evolutionary dead end. And he has kind of a creepy way of maximizing his chances.

Animals such as rats infected with the parasite begin to take more risks and, in some cases, become fatally attracted to the smell of feline urine, and therefore more likely to be killed by them.

For larger animals, such as chimpanzees, this means an increased risk of collision with a larger cat, such as a leopard. Hyenas infected with T. gondii are also more likely to be killed by lions.

gray wolves (Canis lupus) in Yellowstone National Park aren’t exactly cat prey. But sometimes their territory overlaps that of the cougars (concolor puma), known carriers of T. gondiiand the two species both prey on elk (canadian deer), bison (buffalo buffalo) and mule deer (Odocoileus hemionus) that can also be found there.

It’s possible that wolves also get infected, perhaps by occasionally eating dead cougars or ingesting cougar poop.

Data collected on wolves and their behavior for nearly 27 years offered a rare opportunity to study the effects of the parasite on a wild intermediate host.

The researchers, led by biologists Connor Meyer and Kira Cassidy of the Yellowstone Wolf Project, also examined blood samples from wolves and cougars to assess the rate of T. gondii infection.

They found that wolves with a lot of territory overlap with cougars were more likely to be infected with T. gondii.

But there was also a behavioral consequence, with significantly increased risk taking.

Infected wolves were 11 times more likely to disperse from their pack to new territory. Infected males had a 50% chance of leaving their pack within six months, compared to the more typical 21 months for the uninfected.

Similarly, infected females had a 25% chance of leaving their pack within 30 months, compared to 48 months for those who were uninfected.

Infected wolves were also much more likely to become pack leaders. T. gondii can increase testosterone levels, which in turn could lead to increased aggression and dominance, which are traits that would help a wolf assert itself as a pack leader.

This has some important consequences. Pack leaders are those who breed, and T. gondii transmission can be congenital, transmitted from mother to offspring. But it can also affect the dynamics of the whole pack.

frameborder=”0″ allow=”accelerometer; automatic reading; clipboard-write; encrypted media; gyroscope; picture in picture” allow full screen>

“Due to the group life structure of the gray wolf pack, pack leaders have disproportionate influence over their packmates and group decisions,” the researchers write in their paper.

“If the leaden wolves are infected with T. gondii and showing behavioral changes…it can create a dynamic in which the behavior, triggered by the parasite in one wolf, influences the rest of the wolves in the pack.”

If, for example, the pack leader seeks the smell of cougar pee as they push boldly into new territories, they could face greater exposure to the parasite, therefore at a rate of T. gondii infection throughout the wolf population. This generates a sort of feedback loop of increased overlap and infection.

This is compelling evidence that tiny, understudied agents can have a huge influence on ecosystem dynamics.

“This study demonstrates how community-level interactions can affect individual behavior and could potentially extend to group-level decision-making, population biology, and community ecology,” the researchers write.

“Incorporating the implications of parasite infections into future wildlife research is essential to understanding the impacts of parasites on individuals, groups, populations, and ecosystem processes.”

The research has been published in Communications Biology.