Behavioural correlates of Toxoplasma gondii: manipulation or ecological sorting?

Toxoplasma gondii is frequently cited as a paradigmatic example of parasite-induced behavioural manipulation. Across diverse taxa, infected hosts often exhibit elevated risk taking, altered predator responses and changes in social behaviour, patterns commonly interpreted as adaptive modifications that enhance parasite transmission. However, in free-ranging populations, infection status is not randomly assigned: the behaviours most often attributed to manipulation (boldness, dispersal, dominance and habitat exploration) also strongly structure exposure to environmentally transmitted oocysts and trophic infection routes. As a result, behavioural differences between infected and uninfected individuals may arise from ecological sorting rather than parasite-induced change. Here, I argue that behavioural toxoplasmosis in wild systems should be reframed as a problem of causal inference under nonrandom exposure. Drawing on insights from behavioural ecology, disease ecology and neurobiology, I review mechanistic pathways by which T. gondii could influence host behaviour while highlighting the inferential limitations of observational field studies. I then outline methodological strategies capable of disentangling manipulation from exposure-driven selection, including longitudinal within-individual designs, exposure-aware movement models, natural experiments, instrumental variable approaches, mechanism-linked predictions and emerging computational tools for reconstructing latent exposure and behavioural states.