They found that “the odds that a seropositive [infected] wolf becomes a pack leader is more than 46 times higher than a seronegative wolf becoming a pack leader.”.

These scientists assayed samples from 229 individual wolves taken over the years—116 males, 112 females, and one hermaphrodite—to try to correlate the presence of antibodies against the parasite with demographic factors and specific behaviors.

Living in an area of high cougar overlap was the single biggest predictor of a wolf being infected with the parasite, more than any demographic factors like the wolf’s age, sex, or coat color.

Wolves with antibodies against the parasite were significantly more likely to disperse (leave their packs and set out on their own) and to become pack leaders.

Because gray wolves live together in groups, pack leaders have a disproportionate effect on their collective decisions.

An infected leader may increase the overall number of infected wolves, both because pack leaders have a reproductive advantage and because risk-taking leaders might be less hesitant to lead their packs into cougar territory, where they can pick up their own infections.

gondii-infected, aggressive, risk-taking pack leaders can yield “a more assertive, risk-embracing pack culture even though only a few key individuals are actually infected.”.