The influence of sediment type on interactions between Tubifex tubifex and Myxobolus cerebralis: Implications for whirling disease risk

Environmental features may influence interspecific interactions, such as between hosts and parasites.  Myxobolus cerebralis, the parasite causing whirling disease (WD) in salmonids, alternates between a salmonid and Tubifex tubifex, and two free-living spore stages.  Consequently, environmental features may affect WD risk directly, or indirectly.  Myxobolus cerebralis is established in several spawning tributaries to the Yellowstone River and Yellowstone Lake in Yellowstone National Park.  The infected tributaries vary considerably in their geomorphology and WD risk, and we have shown that unconfined reaches, characterized by fine sediments (e.g., silt and clay), had high WD risk, whereas confined reaches, characterized by coarser grained sediments had low risk, and that abundances of T. tubifex and infected T. tubifex were highest in unconfined reaches.  We used a factorial experiment to test the hypotheses that variable sediment types (coarse sand, fine sand, and silt/clay) result in differential 1) survival, growth and reproduction of T. tubifex, and 2) infection prevalence and severity in T. tubifex.  Treatments were exposed to M. cerebralis on each sediment type and then transferred to one of each sediment type.  Survival, growth, and reproduction varied among sediment types.  All positive treatments produced infective spores, however, infection prevalence and severity varied among sediment types.