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Organisms have evolved diverse strategies to manage parasite infections. Broadly, hosts may avoid infection by altering behaviour, resist infection by targeting parasites or tolerate infection by repairing associated damage. The effectiveness of a strategy depends on interactions between, for example, resource availability, parasite traits (virulence, life‐history) and the host itself (nutritional status, immunopathology). To understand how these factors shape host parasite‐mitigation strategies, we developed a mathematical model of within‐host, parasite‐immune dynamics in the context of helminth infections. The model incorporated host nutrition and resource allocation to different mechanisms of immune response: larval parasite prevention; adult parasite clearance; damage repair (tolerance). We also considered a non‐immune strategy: avoidance via anorexia, reducing intake of infective stages. Resources not allocated to immune processes promoted host condition, whereas harm due to parasites and immunopathology diminished it. Maximising condition (a proxy for fitness), we determined optimal host investment for each parasite‐mitigation strategy, singly and combined, across different environmental resource levels and parasite trait values. Which strategy was optimal varied with scenario. Tolerance generally performed well, especially with high resources. Success of the different resistance strategies (larval prevention or adult clearance) tracked relative virulence of larval and adult parasites: slowly maturing, highly damaging larvae favoured prevention; rapidly maturing, less harmful larvae favoured clearance. Anorexia was viable only in the short term, due to reduced host nutrition. Combined strategies always outperformed any lone strategy: these were dominated by tolerance, with some investment in resistance. Choice of parasite mitigation strategy has profound consequences for hosts, impacting their condition, survival and reproductive success. We show that the efficacy of different strategies is highly dependent on timescale, parasite traits and resource availability. Models that integrate such factors can inform the collection and interpretation of empirical data, to understand how those drivers interact to shape host immune responses in natural systems. [ABSTRACT FROM AUTHOR]

The nutrient content of host resources can influence the abundance of parasites within an ecosystem, but linking specific nutrients in a host to the abundance of different parasite taxa remains a challenge. Here, we work to forge this link by quantifying the relationship between the nutrient content of specific infection sites and the abundance of multiple parasite taxa within the digestive tract of largemouth bass (Micropterus salmoides) collected from the Mississippi River. To generate a mechanistic understanding of these relationships, we tested four basic predictions: (1) the nutrient content of different host tissues (infection sites) varies within and across hosts, (2) the nutrient content of parasite genera differs from that of their host tissue(s), (3) the nutrient content of parasite genera differ from one another and (4) the nutrient content of host tissues is related to the nutrient content and abundance of parasite genera. We found support for each of these predictions. We found stoichiometric differences between the digestive tissues we examined. We also found that across hosts, intestine and pyloric caeca C:N ratios increased and %N decreased with fish condition factor. Both of the actively feeding parasitic genera we measured had lower C:N ratios compared to both their host tissue and other encysted/non‐reproductive genera, suggesting the potential for N limitation of these parasites in the intestines or pyloric caeca of hosts. Consistent with this possibility, we found that the total number of actively feeding parasitic worms in the pyloric caeca increased with that tissue's N:P ratio (but was not related to host condition factor). Our results suggest that parasites encounter significant variation in nutrient content within and across hosts and that this variation may influence the abundance of actively feeding parasites. This work highlights the need for additional empirical comparisons of parasite stoichiometry across tissues and individual hosts. [ABSTRACT FROM AUTHOR]