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.

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 who have had toxoplasmosis are more likely to become alpha, a US study shows.

Gray wolves infected with toxoplasmosis become pack leaders far more often than uninfected conspecifics. This is reported by US scientists in the journal "Communications Biology". The neuroparasite probably makes the animals more aggressive, which could be an advantage in the fight for leadership. Wolves infected with the protozoa Toxoplasma gondii are 46 times more likely to become pack leaders.

It is already known for many animal species that such an infection changes their typical behavior significantly. 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 to entrepreneurship and a connection to pathological short temper. However, all of these studies only show correlations, not a causal connection.

For the current study, the team led by US 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. In addition, they took blood samples from 229 anesthetized animals, which they examined for antibodies against Toxoplasma gondii.

The biologists observed that infected wolves behaved more risky. On the one hand, this was reflected in a greater likelihood 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 produces eggs (oocytes) only in cells of the cat's intestinal lining. The eggs are shed in a cat's feces and can cause infection after 1 to 5 days. Eggs in the soil remain infectious for months.

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

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