Wolves, how is the pack leader chosen? From a parasite


Toxoplasma gondii is a protozoan parasite capable of infecting any warm-blooded species and is what causes Toxoplasmosis . The life cycle of  Toxoplasma gondii has two types of reproduction, sexual in felines (definitive host), and another host (intermediate) in which asexual reproduction takes place. The intermediate hosts of T. gondii can be rodents, humans, canids .


The parasite has been shown to change host behavior : infected rats and mice are less fearful than cats, and wolves are reportedly more courageous.

Despite extensive laboratory investigations into the behavioral effects of T. gondii infection, little is known about the effects of toxoplasmosis on the behavior of wild intermediate hosts. Yellowstone National Park, Wyoming, USA has a diverse carnivore community including gray wolves (Canis lupus) and cougars(Puma concolor), respectively intermediate and definitive hosts of T. gondii. In the recent study, the researchers used the resulting data from 26 years of wolf behavioural, spatial and serological monitors to demonstrate that the overlap of wolf territory with areas of high cougar densities is an important predictor of infection. The team also documented information about their social status. An important element that emerged thanks to this research is that HIV-positive wolves (i.e. virus carriers even if not affected by the disease) have shown much more ambition as leaders. They found those infected were 11 times more likely than those uninfected to leave their family of origin to founda new pack and 46 times greater than becoming pack leaders , who are often the only wolves in the pack to reproduce.

Given the social hierarchy within a wolf pack, the researchers hypothesized that the parasites have important implications for intermediate hosts beyond acute infections. In particular, in a social species, these impacts can go beyond individuals and affect groups , populations and even ecosystem processes.

  • Parasitic infection increases risk-taking in a social, intermediate carnivore host. (


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