Divergence and parallelism of parasite infections in Arctic charr morphs from deep and shallow lake habitats

Parasite communities can show large differences in species composition between sympatric host species. Here, we assessed how divergent resource use of polymorphic populations of Arctic charr from two environmentally similar sub-arctic lakes was related to parasite community composition. Large similarities in parasite infections were found for both the reproductively isolated littoral-spawning omnivore LO-morph and the profundal-spawning benthivore PB-morph, reflecting cross-lake similarities in resource use. Furthermore, whereas the PB-morph had the lowest richness and abundance of parasite species in both lakes, a third morph, the profundal-spawning piscivorous PP-morph (one lake only), had the highest parasite richness and accumulated parasites by preying upon fish. These results highlight that host ecology and abiotic factors are important for structuring parasite communities. The dissimilarities in the local parasite species pool between the lakes suggest that stochastic events as well as transmission abilities are involved in structuring the parasite communities. The parallel divergent parasite infections between morphs may form an arena for parasite-mediated selection promoting the incipient speciation process in concert with other factors. The deep-water PB-morphs may avoid parasites by specialising in parasite-poor but low-productive habitats, while the piscivorous PP-morph aggregates infections of detrimental parasites through specialising on energetically rich but generally more heavily parasitised prey.