Why Some Wolves Become Leaders of the Pack

A 20-year study has found a surprising reason why some gray wolves become the pack leader. Wolves infected with the parasite Toxoplasma gondii are far more likely to end up as the top dog.

The tiny parasites are well known to cat owners, where they are a common problem. Because T. gondii can only reproduce inside cats, its effect on other animals has been somewhat overlooked. Yet it can infect almost any warm-blooded animal.

It makes wolves bolder

Wolves in certain areas have become middlemen, as the parasites reproduce, move on to other animals, then make their way back to cats to reproduce. In regions where their territory overlaps with large cats like cougars, the infection rate shoots up.

This is when the effects of the parasite start to take hold. The microscopic organisms have found a way of increasing their chances of making it back to a cat. They alter the behavior of their host wolf.

Wolves live in matriarchal packs and many wolves stay with their pack for their entire lives. Others split off to find a mate and start a pack of their own. Wolves infected with the parasite are 11 times more likely to start a pack of their own and 46 times more likely to become a pack leader.

A grey wolf snarls.

Photo: Shutterstock


The parasite makes the wolves bolder, more aggressive, and more likely to engage in risky behavior. They become alphas because they are more willing to fight other potential top dogs.

The parasite can also pass from mother to offspring. Because it is the pack leaders who reproduce, the parasite can alter the dynamics of the entire group.

The fearlessness instilled by the parasite also makes the pack more likely to wander into cougar territory. There, the parasite has a better chance of making its way back into a cougar to reproduce.

Grey wolves lick each other.

Photo: Shutterstock


No fear of cats

Wolves are not the only animals infected by the behavior-altering parasite. Most species affected by T. gondii are suddenly less scared of their feline predators. Rats are less scared of cats, chimpanzees are no longer afraid of leopards, and hyenas challenge lions. How this happens is not fully understood, but it rarely works in the host animal’s favor.

Researchers believe T. gondii has infected around 33% of humans but the vast majority never know. If you have a healthy immune system, they have very little impact, other than some flu-like symptoms. For those without a strong immune system, the outcome can be very different. Infected people start to produce more testosterone and dopamine. Like wolves, they then take more risks. Lifelong cysts can form in the brain and muscle tissue.

The study shows that T. gondii has a greater impact than anyone envisaged. It not only affects the behavior of wild animals but can change entire ecosystems.

Rebecca McPhee

Rebecca McPhee is a freelance writer for ExplorersWeb.

Rebecca has been writing about open water sports, adventure travel, and marine science for three years. Prior to that, Rebecca worked as an Editorial Assistant at Taylor and Francis, and a Wildlife Officer for ORCA.

Based in the UK Rebecca is a science teacher and volunteers for a number of marine charities. She enjoys open water swimming, hiking, diving, and traveling.