Wolves infected with Toxoplasma are more likely to lead packs, study finds
Oolive trees infected by the parasite Toxoplasma gondii are much more likely to become pack leaders than uninfected wolves and are also more likely to disperse from the pack they were born into, according to a study published November 24 in Communications Biology reports. The discovery points to a possible link between the infamous parasite and the health of the wolf population.
Toxoplasma gondii (T. gondii) is a “mind control” parasite that can infect any warm-blooded animal, the article states. The protozoan can only reproduce sexually in the entrails of cats and is often spread through contact with infected feline feces. infection by T. gondii causes hosts to accumulate permanent brain cysts and also induces toxoplasmosis, a disease that can embolden some host species, causing infected animals to seek out more situations in which they can transmit the parasite. mice infected with T. gondii lose their fear cat urine, for example, making them more likely to be killed and eaten by a cat, allowing the parasite to reproduce again. Studies on hyenas found that cubs infected with T. gondii are more likely to venture into areas where they could be killed by lions. T. gondii also persists in no less than a third of the human population, Nature reports, but the implications of these often asymptomatic infections are not fully understood.
See “animal mind control”
Researchers at the University of Montana wanted to determine if T. gondii induced risk behavior in gray wolves (Canis lupus) in Yellowstone National Park. Yellowstone Wolves spatially overlap with T. gondii-wearing cougars (concolor puma), and the cases of T. gondii infection in wolves has previously been documented, the researchers write in their study. They analyzed existing blood samples taken over more than two decades from 229 Yellowstone wolves and 62 cougars, to determine when and if they were infected with T. gondii. They also looked at pre-existing data collected over those two decades on the locations of members of both species, as well as the age, sex, social status and classification of wolves (if they were in a pack) at each sample point. Wolves that went to areas with more cougars were more likely to contract the disease, the researchers found. Not only that, but they determined that wolves with toxoplasmosis were 46 times more likely to become pack leaders, possibly due to the increased boldness typically associated with the disease.
“We got this result and we just stared at each other in awe,” said Connor Meyer, a University of Montana wildlife ecologist and co-author of the study. Nature. “It’s a lot bigger than we thought.”
Infected wolves were also 11 times more likely to disperse from their birth pack and to disperse at a younger age. Male wolves positive for T. gondii had a 50% chance of dispersing within six months of its first monitoring by the park, which the newspaper said usually begins about six months after the wolf was born. Typically, the 50% dispersal rate for males would be reached 21 months after the start of monitoring. T. gondii– positive females had a 25% probability of dispersing after 30 months, whereas they generally reached this probability 48 months after the start of monitoring.
See “Large carnivores under siege”
The study is one of the few to examine the effects of T. gondii in nature, Science reports.
“The findings likely represent the tip of the iceberg regarding the importance of the parasite to the dynamics of wild ecosystems,” Eben Gering, a biologist at Nova Southeastern University who was not involved in the work, told the magazine.
The dangers of toxoplasmosis in wolves likely outweigh the potential benefits, says Kira Cassidy, study co-author and wildlife ecologist at the Yellowstone Wolf Project. Science. Wolves who leave their pack behind may be more likely to leave the safety of the park or be hit by oncoming vehicles, for example. Cassidy adds that infection with toxoplasmosis can complicate pregnancies, so pack leaders with toxoplasmosis could jeopardize reproduction by spreading the pathogen through mating. In addition, the authors write in the study that it is possible T. gondii– Infected pack leaders could lead their packs into riskier territory, increasing their encounters with cougars. Meyer tells Science that wolves are probably a “no way out” host; cougars almost never eat wolves, so T. gondii has no way of finding a new host to reproduce. However, he posits that the parasite’s effect on wolves, which are a keystone species, could nonetheless shape Yellowstone’s ecosystem.
“Parasites could have a much larger role than anyone generally assigns to them,” Meyer said. Nature.