Wolves in Yellowstone US Park are involved in a love triangle with cougars and a parasite that infects both species. the parasite, Toxoplasma gondiithe wolves’ behavior appears to be changing, making them more audacious toward cougars—and therefore more likely to infect cougars. That was at the end of last week in the Naturemagazine Communication Biology.
T. gondii is a single-celled parasite that can infect a variety of mammals, with cats as the main host. Humans can also become infected with it. If they become ill – with fatigue as a symptom, among other things – then we speak of toxoplasmosis. People usually ingest the parasite through cat feces.
Yellowstone wolves become infected by eating cougar meat or faeces. Cougars are their competitors and enemies in the park. Only the bravest wolves actively seek out cougar territories. The American research now suggests that this is no coincidence: it is a self-reinforcing process. It’s those bravest wolves that are most at risk of contamination – and it’s the contamination that makes them braver.
The latter effect has already been shown in previous studies, including experiments with mice. They became more careless towards cats after being infected by T. gondii, according to an article in PLoS One in 2013. For example, they run a greater risk of being eaten by cats, after which the parasite can reproduce in those cats. Research on hyenas showed that infected animals show less fear of lions than uninfected animals. That was in 2021 in Nature Communications. There, too, the parasite seems to manipulate its intermediate host for its own gain.
Group leader
The research in Yellowstone builds on this hypothesis. In the national park, which is the size of our three northern provinces, the researchers tracked a total of 229 wolves over 27 years. They did this with radio transmitters, sight observations, blood and DNA tests, among other things. As a result, they know exactly the family structure and distribution of many generations of wolves in the park.
Roughly one in three wolves in Yellowstone carry the parasite, the researchers found. Infected and uninfected animals appeared to behave differently. Infected animals were eleven times more likely to leave their natal group in search of a new group. Their chance of becoming a group leader was even 44 times higher.
But what is cause and effect? Does the parasite change wolf behavior, or are the bolder animals simply more at risk of infection? Both, according to the American researchers. There is a complex interplay of effects that influence each other. They draw this conclusion based on previous research – not only the assertiveness studies in rodents and hyenas, but also studies that show that infected animals produce more substances such as dopamine and testosterone. They promote aggressive and risky behavior and reduce fear of the unknown.
“This is really a treat for ecologists,” responds Hugh Jansman of Wageningen Environmental Research, who studies wolves in the Netherlands. “It illustrates very nicely how everything in nature is interrelated. That behavioral aspect is immensely fascinating. You only discover something like that if you monitor an entire ecosystem for decades.”
Stray cats running loose
Toxoplasmosis has not yet been diagnosed in Dutch wolves, the Dutch Wildlife Health Center of Utrecht University said when asked – but few dead wolves have been examined here either. “Anyway, I think that the assertiveness of wolves is also an important factor for us,” says Jansman. “It is precisely the less shy animals that come here from Germany and who manage to survive here, in our anthropogenic landscape. So that gives a selection of assertive animals.”
In addition, T. gondii can also have an effect in the Netherlands in the long term, Jansman thinks, with so many stray cats and house cats spreading the parasite. “This study underscores once again the importance of species interactions,” he says. “Everything seems to be connected. So it would be good if we also keep a close eye on that here for a long time.”