6533b7d0fe1ef96bd125a30c

RESEARCH PRODUCT

Experience and dominance in fish pairs jointly shape parasite avoidance behaviour

subject

description

There is increasing evidence that the composition of a social group influences the fitness of its members. For example, group member identities can determine the exposure risk to contact-transmitted parasites and consequently impact the health of all group members. Here, we propose that group composition may also affect host exposure to parasite propagules prevailing in the environment via collective parasite avoidance behaviours. We explored the spatial avoidance of a trematode parasite, Diplostomum pseudospathaceum, using the simplest form of host groups, pairs of sea trout, Salmo trutta trutta. These pairs showed either (1) between-group heterogeneity in their experience with the parasite (both, one or neither previously exposed) and matched dominance ranks (assessed through growth rates) or (2) within-group heterogeneity in previous exposure and in dominance ranks. We show that pairs that had recently been exposed to the parasite spent significantly less time in areas of infection risk than pairs in which one or both individuals were unexposed. This result suggests that previous exposure improves parasite avoidance. Among pairs with mixed exposure history, parasite avoidance was most pronounced when the exposed individual was dominant over its partner. We conclude that higher ranked individuals direct collective movements and their exposure history predicts a pair's parasite avoidance. As avoidance efficiency was directly related to infection rate, our results suggest that group composition can shape individual exposure to nonsocially transmitted parasites, and ultimately fitness.