Elemental content of a host-parasite relationship in the threespine stickleback

Parasite infections are ubiquitous and their effects on hosts could play a role in ecosystem processes. Ecological stoichiometry provides a framework to study linkages between consumers and their resource, such as parasites and their host, and ecosystem process; however, the stoichiometric traits of host-parasite associations are rarely quantified. Specifically, it is unclear whether parasites' elemental ratios closely resemble those of their host or if infection is related to host stoichiometry, especially in vertebrate hosts. To answer such questions, we measured the elemental content (%C, %N, and %P) and molar ratios (C:N, C:P, and N:P) of parasitized and unparasitized Gasterosteus aculeatus (three-spined stickleback) and their cestode parasite, Schistocephalus solidus. Host and parasite elemental content were distinct from each other, and parasites were generally higher in %C and lower in %N and %P. Parasite infections were related to host C:N, with infected hosts being lower in C:N. Parasite elemental content was independent of their host, but parasite body mass and parasite density were important drivers of parasite stoichiometry. Overall, these potential effects of parasite infections on host stoichiometry along with parasites' distinct elemental compositions suggest parasites may further contribute to differences in how individual hosts store and recycle nutrients.

Automated summary

Parasite infections have widespread effects on hosts and could influence ecosystem processes. However, the stoichiometric traits of host-parasite associations are rarely quantified, and it is unclear whether parasites' elemental ratios resemble those of their host or if infection is related to host stoichiometry. In this study, the elemental content and molar ratios of parasitized and unparasitized stickleback fish and their cestode parasite were measured. The results showed distinct elemental compositions between hosts and parasites, and parasite stoichiometry was influenced by parasite body mass and density. These findings suggest that parasite infections may have important effects on host stoichiometry and nutrient cycling.