Parasite makes pack leader: infection gives wolves a career boost

Parasite makes pack leader
Infection gives wolves a career boost

In a wolf pack, infection with a parasite makes the difference in who is more likely to become the pack leader. Gray wolves that have had toxoplasmosis are more likely to become alpha, according to a US study.

Gray wolves infected with toxoplasmosis become pack leaders much more often than uninfected conspecifics. American scientists report this in the journal “Communications Biology”. The neuroparasite probably makes the animals more aggressive, which can be an advantage in the battle for leadership. 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 road traffic behavior among infected people, a greater urge for entrepreneurship and an association with pathological hot temper. However, all these studies only show correlations, not causation.

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 (Canis lupus) 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.

Benefit to the pathogen

The biologists saw that infected wolves behaved more risky. 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. It has a similar effect when infected animals become pack leaders.

Toxoplasma gondii is distributed worldwide wherever there are cats. This is because the parasite only produces eggs (oocytes) in cells of the cat’s intestinal wall. The eggs are excreted in a cat’s feces and can cause an infection after 1 to 5 days. Eggs in the ground remain contagious for months.

Healthy people usually do not notice the infection with the pathogen at all and remain symptom-free. If a person with a weakened immune system becomes ill, for example due to an organ transplant or HIV disease, an infection with toxoplasmosis can also lead to encephalitis.

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