Background/Question/Methods Parasites are found in nearly all organisms and can profoundly influence host behavior and physiology. Although some of these impacts have been studied in great detail, disease ecologists have only recently begun to explore how parasitism of consumer species may alter nutrient recycling and stoichiometry. Unifying the concepts of ecological stoichiometry and consumer-driven nutrient recycling, we explored how trematode infections in a freshwater pulmonate snail alter carbon and nitrogen assimilation. Snails were separated into infected and uninfected groups of equal mass and fed a standardized diet for two weeks. Following this period, snails were placed in individual tubes for 3-hour excretion trials and subsequently placed in individual jars with known food quantities for foraging and egestion measurements. Additionally, we counted parasite propagules, measured parasite C and N, and estimated parasite mass to determine C and N loss directly associated with parasite biomass.
Results/Conclusions Data analysis showed that infected snails had a negative N assimilation efficiency suggesting severe protein catabolism and/or starvation. However, C assimilation was not variable between infected and uninfected individuals. Interestingly, despite having similar shell-on wet mass, shell-off dry mass was lower in the infected snails. Our results suggest that while carbon assimilation is minimally impacted by trematode infection, infected hosts have potentially severe nitrogen deficits. These results are complicated by measurements of host size which suggests a shift in resource allocation to shell growth in infected snails. This result may help explain gigantism - the observation that trematode infected snails tend to be larger than uninfected snails. Taken together, our results suggest that trematode infection, which is common in freshwater snails, may have underappreciated impacts on nutrient dynamics in freshwater ecosystems.
