Meeting Abstract
Trophically transmitted parasites often adaptively manipulate their intermediate host’s phenotype. These phenotypic changes typically increase transmission to the next host in the life cycle, through greater prey (intermediate host) capture by predatory final hosts. Although final hosts will incur some cost from harboring such parasites, mathematical modelling suggests that there can be a net fitness advantage to preying on manipulated food sources when the energy gained from the parasite “delivery service” outweighs the costs of infection. However, little work has quantified the costs of infection to final hosts of parasites that are known manipulators. This study has examined the costs of infection to final hosts of the trematode parasite Euhaplorchis californiensis (henceforth referred to as Euha). Euha infects the brains of the California killifish, Fundulus parvipinnis, and increases their frequency of conspicuous behaviors, making infected fish 10-30x more likely to be eaten by final host estuarine birds. Euha is a generalist for its final host, theoretically capable of infecting any endotherm that eats infected killifish. As a proxy for estuarine birds, we used lab-reared ducks and chickens that were infected repeatedly for four weeks from ten days post-hatching. In both species, we found no detrimental effects on any trait examined, including growth, skeletal morphology, behavior, hematocrit, immune function, or energy metabolism. This study provides evidence that trophically-transmitted parasites can benefit predatory final hosts by making prey easier to capture, while exerting minimal energetic costs.
