Parasite infection in a central sensory organ of fish does not affect host personality

Among the ecological factors acting on the evolution and expression of animal personalities and behavioral syndromes, parasitism has received comparatively little attention. However, infection and host behavior are often strongly intertwined, because host behavior can predict the risk of infection and can also be changed by an infection. We conducted a controlled experimental infection study to explore the effects of infection on host boldness, exploration and activity using rainbow trout Oncorhynchus mykiss and its trematode parasite Diplostomum pseudospathaceum, which infects a central sensory organ of the fish, the eye lens. Contrary to our expectation, infection did not change the within-individual consistency of the personality traits or the relationships between the traits, but infected individuals were less bold than uninfected control individuals. We also found no relationship between personality in uninfected fish and resistance against parasite infection, suggesting that behaviors which increase parasite encounter do not select for improved resistance. Thus, we found only weak support for parasite-mediated effects on animal personalities.