Water Temperature Affects a Host–Parasite Interaction: Tubifex tubifex and Myxobolus cerebralis

Abstract

The aquatic oligochaete worm Tubifex tubifex is an obligate host of Myxobolus cerebralis, the causative agent of salmonid whirling disease. Tubifex tubifex becomes infected by ingesting M. cerebralis myxospores and releases triactinomyxons (TAMs) into the water that then infect salmonids. In a laboratory experiment, we examined how water temperature influenced changes in oligochaete population size and biomass and the release of TAMs in three genetically identified strains of T. tubifex when exposed and not exposed to M. cerebralis myxospores. Increases in population size and biomass were greatest at 8.0°C for the Gallatin River strain, greatest at 15.0°C for the Madison River strain, and similar at both temperatures for the Mt. Whitney strain. After exposure to M. cerebralis myxospores, Mt. Whitney and Madison River T. tubifex both released TAMs at 15°C beginning on day 88 and at 8.0°C on day 169 (Mt. Whitney strain) and day 182 (Madison River strain); thus, between 1,320 and 1,456 degree-days were required for M. cerebralis to develop. Gallatin River T. tubifex did not release TAMs. We found no evidence that M. cerebralis developed differently in strains of T. tubifex with different temperature requirements; therefore, it appears that temperature-driven parasite development rates are a primary determinant of the timing of TAM release.