Parasite-mediated manipulation? Toxoplasma gondii infection increases risk behaviour towards culling in red deer

Abstract

Parasites can modify host behaviour to increase their chances of survival and transmission. Toxoplasma gondii is a globally distributed protozoan whose ability to modify host behaviour is well known in taxa such as rats and humans. Less well known are the effects on the behaviour of wild species, with the exception of a few studies on primates and carnivores. Taking advantage of a culling activity conducted in Stelvio National Park (Italy), the serological status of T. gondii was studied in 260 individuals of red deer Cervus elaphus with respect to the risk of being culled. A temporal culling rank index was fitted as a response variable, and T. gondii serological status as the main explanatory variable in linear models, accounting for covariates such as sex, age, jaw length, bone marrow fat and culling location. The overall seroprevalence of T. gondii was 31.5%, and the selected models suggested that seropositive deer were culled earlier than seronegative ones, but this effect was only evident in females, in individuals with medium-good body condition, and in areas with greater human presence. Our results suggest that T. gondii may be involved in risk behaviour in large herbivores, supporting its role as a facilitator of predation risk.

Keywords: behavioural changes; culling; host manipulation; parasites; pathogens; wild ungulates.

Figure 1.

Marginal effects of the variables selected to explain variation in culling rank index of red deer in the winter of 2016–17 and 2017–18 in Stelvio National Park: (a) sex; (b) proportion of bone marrow fat; (c) level of human activity by serological status; (d) year of culling.