Date Approved


Graduate Degree Type


Degree Name

Biology (M.S.)

Degree Program



Infectious disease can influence organisms at all levels of ecological organization, from individuals to ecosystems. Likewise, the ecosystems where pathogens exist directly influence their success. Recent theoretical studies have tied disease prevalence to biotic factors such as genetic diversity, biodiversity, and host behavior, and abiotic factors that include temperature and increased nutrient concentrations. Parasites included in the phylum Microspora are increasingly recognized for being ubiquitous in nature, although their ecological roles are generally unknown. This study examined several environmental, community, and host-related metrics to compare the biotic and abiotic aspects of 16 small streams; 6 with mottled sculpin (Cottus bairdii) populations infected by the microsporidian Glugea sp., and 10 without the parasite. Comparisons were made between the condition of infected and uninfected mottled sculpin. Relatively high water temperatures were implicated in the presence of the parasite, although the fish assemblages did not differ significantly between streams with and without Glugea. Evidence of the consequences of infection was limited to reductions in liver somatic indices and increases in the somatic mass at age for infected individuals, as well as reductions in gene diversity and Wright’s inbreeding coefficient. No significant differences were detected in host densities, host sex ratios, relative abundances, or mortality rates, and there was an absence of genetic bottlenecks in infected mottled sculpin populations. Together, these findings suggested that host population dynamics were generally unaffected by the disease. Contrary to previous ecological research on microsporidian species, mottled sculpin populations appear to be robust to infection, which is likely due to the strong density-dependent population dynamics of mottled sculpin that allow for losses due to disease to be compensatory and quickly offset. This study provides basic ecological insight into the role of microsporidian parasites in natural ecosystems.