Is the probability of a wolf wanting to become the wolf king related to Toxoplasma? Research shows: The probability is 46 times higher

Produced by: Science Popularization China

Author: EVEE (School of Life Sciences, Peking University)

Producer: China Science Expo

"I will accompany you in those adventurous dreams of yours..."

You would never have thought that this romantic song would also be suitable for Parasite.

What? Wolves infected with parasites are more likely to become pack leaders?

Everyone is probably familiar with wolves. In various movies, TV shows and literary works, wolf packs and wolf kings often appear on screen. Similarly, everyone is certainly familiar with parasites. There are many news related to parasite infections on the Internet.

Wolf Pack

(Photo source: Veer Gallery)

But in our impression, being infected with parasites is not a good thing. Why is it that in a wolf pack, wolves infected with parasites have a greater probability of becoming wolf kings? Why is this?

Mountain lions and gray wolves in Yellowstone Park

A recent study found that gray wolves in Yellowstone National Park in the United States who were infected with a parasite were more than 46 times more likely to become leaders of the pack than their uninfected companions . The parasite that makes wolves more capable of leadership is called Toxoplasma gondii , also known as Toxoplasma gondii, the only species of the genus Toxoplasma in the family Sarcocystis.

The ultimate host of Toxoplasma gondii is cats, because they can only reproduce sexually in cats, and all other hosts are intermediate hosts. Toxoplasma gondii can cause toxoplasmosis, which usually has mild symptoms and can heal itself, but can cause serious or even fatal damage to the fetus and people or cats with immune deficiencies. You may not imagine that research data shows that 30-50% of the world's population has been exposed to and chronically infected with Toxoplasma gondii, and the positive infection rate of Toxoplasma gondii in my country is 5%-20%, and in some areas it is as high as more than 30%.

Toxoplasma gondii

(Image source: Wikipedia)

After talking about Toxoplasma gondii, let's talk about the gray wolves in Yellowstone Park. Although wolves could be seen everywhere in Yellowstone Park when it was first established, people wanted to obtain valuable wolf skins and used strychnine to kill the gray wolves in the park. After 1926, it was difficult to see gray wolves in Yellowstone Park. It was not until 1995 that people caught 14 gray wolves in western Canada and released them into Yellowstone Park, and the wolf pack began to reproduce in the park again.

But how did the gray wolves in Yellowstone Park become infected with Toxoplasma?

This has to start with the wolf's old rival, the cougar. The cougar is a feline. As mentioned above, cats are the final host of Toxoplasma, so the cougar, which is also a feline, is also likely to be the final host of Toxoplasma. The researchers also confirmed this based on the serum test results of 62 cougars. Therefore, Toxoplasma can reproduce sexually in cougars to form oocysts, and the oocysts will further spread in the environment through the activities of cougars.

Cougar

(Image source: Wikipedia)

As the top predator in Yellowstone Park, the introduced gray wolves continued to expand their territory, and soon they came into contact with the "native" mountain lions in the park. There is a fierce competition for survival between gray wolves and mountain lions. Studies have shown that gray wolves will use their numerical advantage to snatch food from mountain lions, and even fight with mountain lions and kill mountain lion cubs. Although gray wolves are the winners most of the time, contact with mountain lions also inevitably makes them infected with Toxoplasma.

Toxoplasma makes gray wolves more adventurous

Since 1995, scientists have conducted a 26-year follow-up observation on the introduced gray wolves. It is this long-term observation that allows people to glimpse the huge impact of Toxoplasma gondii on gray wolves.

Specifically, scientists obtained 26 years of behavior and distribution data of wolves. In addition, they anesthetized 229 wolves to obtain blood samples to detect antibodies to Toxoplasma. The results showed that compared with wolves whose living areas were far away from the areas where mountain lions were active, wolves whose territories overlapped with areas with high mountain lion density were more likely to be infected with Toxoplasma. In other words, gray wolves were most likely to be infected with Toxoplasma due to direct contact with mountain lions or the environment where mountain lions were active.

In general, wolves whose territories overlapped with mountain lions' ranges (purple) were more likely to be infected with Toxoplasma.

(Image source: References)

Furthermore, scientists found that both female and male gray wolves, after being infected with Toxoplasma gondii, have a higher probability of engaging in some high-risk behaviors, including leaving the wolf pack and even approaching humans.

In the wild, wolves usually move around in family units. When young wolves grow up, they usually leave their parents to form their own families. In Yellowstone Park, the situation is slightly different. Because the prey density is relatively high and the territory is small, scientists have found that wolf pups will live with their parents for a longer time. A wolf pack may consist of parents and offspring born in four years. For young wolves in a wolf pack, leaving the wolf pack is a very dangerous thing. After all, a wolf cannot defeat a mountain lion in most cases.

However, infection with Toxoplasma changed the wolves in Yellowstone. Male gray wolves that tested positive for Toxoplasma had a 50% chance of leaving the pack within six months of monitoring, while uninfected gray wolves had a 50% chance of leaving the pack about 21 months after monitoring.

Similarly, female gray wolves infected with the parasite had a 25% chance of leaving the pack within 30 months of being monitored, while uninfected females took 48 months to make a similar decision.

Wolf pack composition and behavior analysis results, red represents Toxoplasma-positive wolves, black represents Toxoplasma-negative wolves

(Image source: References)

Overall, infection with T. gondii made wolves 11 times more likely to leave the pack to start their own families, and those gray wolves that tested positive for T. gondii were 46 times more likely to become pack leaders than their uninfected counterparts.

It's really surprising that such a small parasite can have such a big impact on the wolf pack.

Risks and benefits coexist, infection is a double-edged sword

Previous studies have found that infection with Toxoplasma gondii can lead to increased testosterone production in rats and increased bold and reckless behavior in hyenas. Regarding the risk-taking behavior of Toxoplasma-positive gray wolves, the researchers speculate that a similar mechanism exists in gray wolves, and perhaps Toxoplasma infection can lead to changes in hormone levels in gray wolves.

Regardless, infection with Toxoplasma has a profound impact on the gray wolf population. In some cases, gray wolves infected with Toxoplasma can become very successful because they are more willing to take risks, constantly push boundaries, and become leaders who may also lead their own tribe to a brighter future.

It is undeniable that the adventurous behavior of gray wolves that are positive for Toxoplasma also brings risks. Earlier, we mentioned the competition between wolves and mountain lions in Yellowstone Park. Infected gray wolves may go to higher-risk areas that overlap with the range of mountain lions. Without their numerical advantage, they are no match for mountain lions if they fight alone.

Not only that, wolves that wander around may be more likely to be hit by cars or leave protected areas and eventually be shot by hunters. Infected wolf pack leaders may also spread the parasite during mating, making it more difficult for females to become pregnant and produce healthy offspring.

There is no doubt that for gray wolves, infection with Toxoplasma gondii is actually a double-edged sword, with both risks and benefits behind risky behavior. If gray wolves can choose for themselves, will they choose to be infected or choose to live a routine life?

Editor: Sun Chenyu

References:

【1】Meyer, CJ, Cassidy, KA, Stahler, EE, Brandell, EE, Anton, CB, Stahler, DR, & Smith, DW (2022). Parasitic infection increases risk-taking in a social, intermediate host carnivore. Communications Biology, 5(1), 1-10.

【2】Sands, J., & Creel, S. (2004). Social dominance, aggression and faecal glucocorticoid levels in a wild population of wolves, Canis lupus. Animal behaviour, 67(3), 387-396.

(Note: Latin text should be italicized.)