Weak effects of a microsporidian parasite on mottled sculpin in Michigan streams

Abstract

Despite the widespread occurrence of microsporidian parasites in vertebrates and many invertebrates, research regarding their effects on wild populations remains uncommon. We used several metrics of individual growth, condition, and population characteristics to evaluate the effects of a microsporidian infection (Glugea) on six infected populations of mottled sculpin (Cottus bairdii) compared with 10 nearby uninfected populations. Infected individuals (n = 129) were significantly heavier in each age class when compared with uninfected fish (n = 331), yet other measures of growth and condition indicated little influence of the parasite. No significant parasite-associated effects were found when comparing mortality rates, mean age, sex ratios, and history of population genetic bottleneck between infected and uninfected populations. Additionally, we did not detect significant differences in environmental variables or fish assemblages between streams with and without the parasite. Given the disfiguring nature of infection and the strong effects of microsporidian parasites on other hosts, the lack of significant effects caused by parasitism was unexpected and is likely attributed to strong host density-dependent population dynamics or relatively low host infection intensities.Résumé : Bien que les microsporidies parasites soient répandues chez les vertébrés et de nombreux invertébrés, les travaux sur leurs effets sur les populations sauvages demeurent assez rares. Nous avons utilisé plusieurs mesures de la croissance et de l'état individuels et des caractéristiques de la population pour évaluer les effets d'une infection à microsporidie (Glugea) sur six populations infectées de chabot tacheté (Cottus bairdii) par rapport à 10 populations non infectées voisines. Si les individus infectés (n = 129) étaient significativement plus lourds dans chaque catégorie d'âges comparativement aux poissons non infectés (n = 331), d'autres mesures de la croissance et de l'état indiquaient peu d'influence du parasite. Aucun effet significatif associé au parasite n'a été noté sur le plan des taux de mortalité, de l'âge moyen, du rapport des sexes et de l'historique de goulots d'étranglement génétiques entre les populations infectées et non infectées. En outre, nous n'avons décelé aucune différence significative des variables du milieu ou des assemblages de poissons entre les cours d'eau avec et sans parasites. Étant donné l'effet défigurant de l'infection et les effets importants de microsporidies parasites sur d'autres hôtes, l'absence d'effets significatifs causés par le parasitisme était inattendue et serait vraisemblablement attribuable à une dynamique de la population fortement dépendante de la densité des hôtes ou des intensités d'infection relativement faibles des hôtes. [Traduit par la Rédaction]

Distribution, prevalence, and pathology of a microsporidian infecting freshwater sculpins

“…High prevalence can be maintained for multiple years as shown by Seven Mile Creek, where prevalence ranged from 69 to 93% between 2007 and 2011. Prevalence can also fluctuate substantially; in 2007, prevalence in Silver Creek sculpin was 11% but reached 75% in 2011 (Homola et al 2014). However, prevalence in age-0 fish was very low.…”

“…Additionally, any negative effects on individuals could be significant at the population level given the higher infection intensity in females and the high prevalence in general. However, work on these populations by Homola et al (2014) suggests that individual-and population-level effects are weak. While studies of rainbow smelt populations from multiple locations, including Lakes Erie and Ontario, showed that G. hertwigi reduced reproduction and increased mortality (Chen & Power 1972, Nepszy & Dechtiar 1972, Scarborough & Weidner 1979, models indicated no correlation between infection prevalence and smelt recruitment in Lake Erie over a 20 yr study (Henderson & Nepszy 1989).…”

“…The streams are: Rice Creek, Seven Mile Creek, and Wilder Creek (Calhoun County); Augusta Creek, Castle Creek, Lee Creek, Portage Creek, Sand Creek, Silver Creek, and Spring Brook (Kalamazoo County) and Curtis Creek (St. Joseph County) (Homola et al 2014). We captured sculpin using a backpack electroshocker and attempted to collect at least 30 fish in each stream.…”

“…Mottled sculpin C. bairdii populations from several southwest Michigan (USA) streams are infected by a microsporidian parasite that causes the formation of xenomas in the body cavity of fish ( Fig. 1) (Homola et al 2014).…”

Infection by the cestode parasiteSchistocephalussp. and effects on diet, body condition and survival of sculpinsCottus aleuticusandCottus cognatus

“…The data indicated that C. aleuticus (but not C. cognatus ) with cestodes were heavier for their L T (after removal of the cestodes themselves from the fish) than conspecifics without cestodes, although L T at age did not differ in either species. This effect in condition factor was unexpected but consistent with the weak and very mixed effects of a microsporidian parasite on growth and condition in a different sculpin species (Homola et al , ).…”