Is Habitat Type a Useful Predictor of the Outcome of Interactions between Tubifex tubifex and Myxobolus cerebralis, the Causative Agent of Salmonid Whirling Disease?

The aquatic oligochaete Tubifex tubifex is the intermediate host for the parasite, Myxobolus cerebralis, which causes salmonid whirling disease (WD). Although the relationship between WD severity in salmonids and infection in T. tubifex is not well understood, previous research suggests that variation within local stream populations of T. tubifex may be an important determinant of parasite success. Our goals were to examine relationships among habitat features, abundance, infection prevalence, genetic diversity and susceptibility of T. tubifex, and WD risk in Yellowstone cutthroat trout spawning tributaries in Yellowstone National Park, where M. cerebralis was detected in 1998. Abundance of tubificids and T. tubifex, and infection prevalence in T. tubifex were higher in unconfined habitat types than in confined habitat types. Tubifex tubifex belonging to mtDNA lineages III, which are considered moderately susceptible to M. cerebralis, were also more abundant in unconfined habitats than confined habitats. We assessed the susceptibility of four genetically distinct strains of lineage III T. tubifex to M. cerebralis in the laboratory. Strains were established from field collected T. tubifex. All strains were susceptible to infection by M. cerebralis and strains from unconfined habitats amplified the parasite only slightly more than strains from confined habitats. These results suggest habitat type may influence variability in WD risk by affecting the outcome of interactions between T. tubifex and M. cerebralis in the field.