Ua study of 26 years of behavioral data on wolves and blood analysis of 229 wolves found that infection with the parasite Toxoplasma gondiii makes wolves 46 times more likely to become pack leaders.
Header image: a wolf in Yellowstone National Park. (Yellowstone Wolf Project)
This research shows that the effects of this parasite in nature have been vastly understudied and that its role in ecosystems and animal behavior has been underestimated.
If you have a cat, you’ve probably heard of this parasite. This microscopic organism can only reproduce in the body of felines, but it can infect and thrive in almost any warm-blooded animal.
We can’t say that your Guru is a “fan” of this parasite, but he is passionate about its ability to control its hosts, as you can see by the number of articles (resulting from studies) written about her.
This includes humans, in whom it can (among other things) cause a usually asymptomatic (but potentially fatal) parasitic disease called toxoplasmosis.
The latest research on this parasite and the human, at the beginning of November 2022:
Once in another host, each parasite T. gondii must find a way to bring his offspring back into the chat if he doesn’t want to become an evolutionary dead end. Sure enough, it breeds in the cat’s intestinal tract and it has a pretty scary way of maximizing its chances of getting there.
Animals like rats infected with the parasite begin to take more risks and, in some cases, are attracted by the smell of urine felines, making them more susceptible to being killed by them.
For larger animals, such as chimpanzees, this means an increased risk of encountering 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) from parc national de Yellowstone (Montana/ USA) are not exactly prey for cats. But their territory sometimes encroaches on that of the cougars (Puma concolor), known carriers of T. gondiiand both species prey on elk (Canadian deer), bison (Bison bison) and mule deer (Odocoileus hemionus) that can also be found there.
It is possible that wolves are also infected, perhaps by occasionally eating dead cougars or ingesting cougar droppings.
From the study: Diagram of the possible feedback loop involving gray wolves, cougars and T. gondii. Red numbers indicate seropositive animals and black numbers seronegative animals. Thick, purple arrows indicate links supported by this study or other publications. Thin, gray lines indicate hypothetical relationships. (Meyer, Cassidy et al./ Communications Biology)
Data collected on wolves and their behavior over nearly 27 years offered a rare opportunity to study the effects of the parasite on an intermediate wild host.
The researchers, led by biologists Connor Meyer and Kira Cassidy of Yellowstone Wolf Projectalso examined blood samples from wolves and cougars to assess the rate of infection with the T. gondii. They found that wolves whose territory overlaps with cougars were more likely to be infected with the parasite.
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. The infected males were 50% to leave their pack within 6 months, against 21 months for the uninfected. Similarly, infected females had a 25% chance of leaving their pack within 30 months, compared to 48 months for the uninfected.
A pack of wolves stalking an elk in Yellowstone National Park. (Yellowstone Wolf Project)
Infected wolves were also much more likely to become pack leaders. the T. gondii can increase the rate of testosteronewhich could lead to increased aggression and dominance, characteristics that would allow a wolf to assert itself as a pack leader.
This has some important consequences. Pack leaders are those who reproduce, and the transmission of T. gondii can be congenital, that is, transmitted from mother to offspring. But it can also affect the dynamics of the entire pack.
A wolf and her cubs in Yellowstone National Park. (Yellowstone Wolf Project)
According to the researchers in their study:
Due to the group life structure of the Gray Wolf pack, pack leaders have disproportionate influence over their packmates and group decisions.
If pack leader wolves are infected with T. gondii and show behavioral changes…this can create a dynamic whereby the behavior, triggered by the parasite in one wolf, influences the rest of the wolves in the pack.
If, for example, the pack leader searches for the scent of cougar urine as he boldly ventures into new territory, he could be more exposed to the parasite, increasing the rate of infection from the cougar. T. gondii in the entire wolf population. This generates a sort of feedback loop of increased overlap and infection.
This is irrefutable proof that tiny, little-studied agents can have a considerable influence on the dynamics of ecosystems.
According to the researchers:
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.
Integrating the implications of parasitic infections into future wildlife research is essential to understanding the impacts of parasites on individuals, groups, populations, and ecosystem processes.
The study published in Communications Biology: Parasitic infection increases risk-taking in a social, intermediate host carnivore and featured in Nature: Parasite gives wolves what it takes to be pack leaders.