Ecology of whirling disease in arid lands with an emphasis on Tubifex tubifex

The novel pathogen hypothesis describes host parasite relationships where a pathogen spreads into new geographical areas or into areas of previously unexposed 'virgin' hosts. Often, measures of parasite virulence and host resistance are elucidated through pathogenic impacts on the 'virgin' hosts. The myxosporean Myxobolus cerebralis, the causative agent of whirling disease in salmonid fish, qualifies as a novel pathogen with its recent introduction into North America from Europe in the 1950s. This introduction of a novel pathogen provides opportunity for insight into the etiology of host-parasite life cycles, parasite virulence, and host resistance.; The devastating effect of whirling disease on wild salmonid populations was not fully realized until its discovery in the inter-mountain west. The presence of the whirling disease parasite in rainbow trout was confirmed in New Mexico the spring of 1999. The most devastating potential of the parasite in New Mexico lies in the threat it poses to native salmonid populations that rely on natural reproduction.; In this dissertation, I investigated the distribution T. tubifex lineages within waters that support salmonids within the State of New Mexico, ecological relationships and physiological responses to T. tubifex infection with M. cerebralis, and analyzed the genetic divergence between T. tubifex lineages from varied habitats in a system that harbors the parasite. The goal of my research was to establish which T. tubifex lineages are present in arid lands habitat and whether they are differentiated by ecological factors. I clarified the taxonomic status of T. tubifex lineages found in New Mexico through examination of genetic divergence between lineages III and VI. Furthermore, I have investigated the relative susceptibility of the lineages to M. cerebralis to aid in the assessment of risk of parasite establishment in sensitive waters.