Variation in parasite resistance of Arctic charr, Salvelinus alpinus, between and within sympatric morphs

Genetic variation in resistance against parasite infections is a predominant feature in host-parasite systems. However, mechanisms maintaining genetic polymorphism in resistance in natural host populations are generally poorly known. We explored if differences in natural infection pressure between resource-based morphs of Arctic charr (Salvelinus alpinus) has resulted in differentiation in resistance profiles. We experimentally exposed offspring of two morphs from Lake Þingvallavatn (Iceland), the pelagic planktivorous charr (‘murta’) and the large benthivorous charr (‘kuðungableikja’), to their common parasite, eye fluke Diplostomum baeri, infecting the eye humour. We found that there were no differences in resistance between the morphs, but clear differences among families within each morph. Moreover, we found suggestive evidence of resistance of offspring within families being positively correlated with the parasite load of the father, but not with that of the mother. Our results sug...