Many parasites manipulate the behaviour of their hosts to their own advantage. Few, though, help their victims rise up through the social hierarchy. But that is exactly what happens when wolves become infected with a common parasite.
Toxoplasma is a single-celled parasite that spreads through contact with the faeces or meat of an infected animal. It can only reproduce sexually in members of the cat family, but can proliferate asexually in most mammals, including humans, where it induces changes in behaviour.
“It seems to mess with hormone levels in the brain, which increases risk-taking behaviour,” says Connor Meyer of the University of Montana. This is thought to increase the chances that an animal will end up being eaten by a cat, which would allow the parasite to complete its lifecycle.
Working in Yellowstone National Park, Meyer, co-lead author of the new study published in Communications Biology, found that this cavalier approach to life results in Toxoplasma – infected wolves being 46 times more likely to become pack leaders compared to uninfected ones.
It doesn’t necessarily follow that the wolves are benefiting from infection. “What we don’t yet know is whether they are successful pack leaders,” says Meyer.
A gung-ho attitude is also likely to get infected animals into trouble in other ways. “We know that hyenas infected with Toxoplasma are more likely to be killed by lions,” says Meyer. Yellowstone doesn’t have any cats big enough to take wolves. But that wasn’t always the case. “A few thousand years ago, we’d have had the North American lion here, so the downsides might have been more obvious.”
Main image: Wolves running in Yellowstone National Park, USA © Mark Miller Photos/Getty