Brain‐infecting parasites leave lasting effects on behaviour even in resistant hosts

Abstract

Abstract Parasites can have profound effects on intra‐ and interspecific interactions at the population and community levels through their influence on host behaviour, physiology and fitness. While host phenotypic changes are typically thought of in terms of established infections, parasite encounters may be sufficient to induce behavioural changes, even when no viable infections are established. Here, we use the Japanese rice fish medaka Oryzias latipes and the brain‐infecting microsporidan parasite Pseudoloma neurophilia to understand how parasite resistance influences behaviour. Although a previous study suggested that medaka are a suitable host for P. neurophilia, an eight‐week parasite exposure regime resulted in no detectable infection in our study. Both parasite‐exposed and control (no parasite exposure) medaka were tested in behavioural assays that assessed boldness, activity and sociality. We detected considerable changes in medaka behaviour following parasite exposure, with parasite‐exposed fish being more active, less bold and more social when compared to control fish. These data indicate that parasite encounters may induce behavioural alterations even in non‐susceptible hosts. In addition to established infection, individual differences in parasite exposure must also be considered in studies of host responses across ecological scales. Read the free Plain Language Summary for this article on the Journal blog.