Parasite gives wolves what they need to be pack leaders

(ORDO NEWS) — The study is one of the few to demonstrate the behavioral effects of Toxoplasma gondii in wild animals.

Wolves infected with a common parasite are more likely than uninfected animals to lead a pack, according to an analysis of more than 200 North American wolves. Infected animals are also more likely to leave their flocks and start an independent life.

The parasite, Toxoplasma gondii, makes its hosts bold, a mechanism that boosts its survival rate. To reproduce naturally, T. gondii must be ingested by a cat, usually when its owner eats the cat.

This becomes much more likely if the parasite alters the host’s behavior to make it reckless. In rodents, infection generally correlates with a decrease in fear of cats and an increase in exploratory behavior.

Physical and behavioral changes have also been found in humans, with increased production of testosterone and dopamine and increased risk taking.

Warm-blooded mammals can become infected with the parasite by eating an infected animal or by ingesting T. gondii excreted in the feces of infected cats.

After a period of acute infection, mature cysts form in the muscle and brain tissue, which persist until the end of the host’s life. Up to one third of people can be permanently infected with them.

T. gondii is known to infect wild animals, but few studies have examined its behavioral effects. In one study, infected hyenas in Kenya were more likely to be eaten by lions.

Connor Meyer and Kira Cassidy, wildlife ecologists at the University of Montana at Missoula, recalled a rare opportunity to link the infection to the behavior of wild wolves: data on gray wolves (Canis lupus) has been intensively collected in Yellowstone National Park, Wyoming, for nearly 27 years.

Some wolves in Yellowstone live near cougars (Puma concolor), which are known to carry the parasite, and sometimes steal prey from them. Wolves can become infected by eating cats or their feces.

The team examined 256 blood samples from 229 wolves, which were carefully monitored throughout their lives, recording their life history and social status.

Meyer and Cassidy found that infected wolves were 11 times more likely than uninfected ones to leave their family of origin to start a new pack, and 46 times more likely to become pack leaders often the only wolves in a pack to breed.

“We got this result and just stared at each other with our mouths open,” says Meyer. “It’s a lot more than we thought.

“Parasites can play a much larger role than is commonly believed,” he says.

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