Gray wolves infected with toxoplasmosis become pack leaders much more often than uninfected conspecifics. The neuroparasite probably makes the animals more aggressive, which could be an advantage in the battle for leadership, US scientists report in the journal Communications Biology. Wolves infected with the protozoan Toxoplasma gondii are 46 times more likely to become pack leaders.
In many animal species, such an infection is already known to significantly alter their typical behaviour. Whether the neuroparasite causes behavioral changes in humans is still a matter of controversy. Studies report, among other things, more reckless behavior in road traffic among infected people, a greater urge for entrepreneurship and an association with pathological short temper.
Parasite is widespread
However, all these studies only show correlations, not causation. What is clear is that the parasite, which is related to the malaria causative agent, causes no symptoms or only mild fever in most people and is widespread.
According to current knowledge, it is believed that 30 percent of the world’s population is infected. A study by the Robert Koch Institute showed that half of Germans have the corresponding antibodies in their blood, and even 70 percent of the over-50s.
For the current study, the team led by American biologists Connor Meyer and Kira Cassidy analyzed data on the behavior and distribution of gray wolves collected between 1995 and 2020 in Yellowstone National Park in the US state of Wyoming. They also took blood samples from 229 anesthetized animals, which they tested for antibodies against Toxoplasma gondii (photo below).
Transferred from cougars to wolves
The actual last host of the neuroparasite are felines (Feliformia) – Cougars also live in Yellowstone Park and their distribution has also been recorded. In addition, blood samples from 62 of the big cats were examined. The biologists found that wolves in areas with higher cougar densities were more likely to be infected with T. gondii than wolves that didn’t live near cougars.
In particular, they saw that infected wolves behaved in a more risky way. On the one hand, this was reflected in a higher chance of leaving the pack earlier, both in males and females. Behavior that makes sense with regard to the spread of the pathogen: The pathogen is more likely to reach areas where it has not previously circulated.
Does Parasite Increase Testosterone Levels?
On the other hand, the scientists saw that wolves that tested positive for T. gondii became much more likely to become pack leaders. The parasite could raise the animals’ testosterone levels, they suspect. On the other hand, riskier leaders are more likely to lead their group into areas that overlap with mountain lions, giving the parasite new opportunities for infestation.
Pilot intermediate hosts for predators
According to the authors, the study shows for the first time that a parasitic infection can influence the behavior of wolves. For other species, T. gondii has long been shown to effectively lure its intermediate host near feline species: infected mice and rats, for example, are magically attracted to the smell of cat urine and literally walk into the mouths of their predators.
A research team observed a similar mechanism in chimpanzees: when they contracted toxoplasmosis, leopard urine exerted a morbid attraction on them. And last year, American researchers reported that infection makes spotted hyena pups much more carefree. Instead of staying in the safe parental den, they get dangerously close to lions: Infected pups are much more likely to be killed, the researchers said.