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Abstract Predation on parasites is a common interaction with multiple, concurrent outcomes. Free‐living stages of parasites can comprise a large portion of some predators' diets and may be important resources for population growth. Predation can also reduce the density of infectious agents in an ecosystem, with resultant decreases in infection rates. While predator–parasite interactions likely vary with parasite transmission strategy, few studies have examined how variation in transmission mode influences contact rates with predators and the associated changes in consumption risk.To understand how transmission mode mediates predator–parasite interactions, we examined associations between an oligochaete predatorChaetogaster limnaeithat lives commensally on freshwater snails and nine trematode taxa that infect snails.Chaetogasteris hypothesized to consume active (i.e. mobile), free‐living stages of trematodes that infect snails (miracidia), but not the passive infectious stages (eggs); it could thus differentially affect transmission and infection prevalence of parasites, including those with medical or veterinary importance. Alternatively, when infection does occur,Chaetogastercan consume and respond numerically to free‐living trematode stages released from infected snails (cercariae). These two processes lead to contrasting predictions about whetherChaetogasterand trematode infection of snails correlate negatively (‘protective predation’) or positively (‘predator augmentation’).Here, we tested how parasite transmission mode affectedChaetogaster–trematode relationships using data from 20,759 snails collected across 4 years from natural ponds in California. Based on generalized linear mixed modelling, snails with moreChaetogasterwere less likely to be infected by trematodes that rely on active transmission. Conversely, infections by trematodes with passive infectious stages were positively associated with per‐snailChaetogasterabundance.Our results suggest that trematode transmission mode mediates the net outcome of predation on parasites. For trematodes with active infectious stages, predatoryChaetogasterlimited the risk of snail infection and its subsequent pathology (i.e. castration). For taxa with passive infectious stages, no such protective effect was observed. Rather, infected snails were associated with higherChaetogasterabundance, likely owing to the resource subsidy provided by cercariae. These findings highlight the ecological and epidemiological importance of predation on free‐living stages while underscoring the influence of parasite life history in shaping such interactions.
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This content will become publicly available on January 1, 2026
Age‐prevalence curves in a multi‐species parasite community
Abstract The relationship between infection prevalence and host age is informative because it can reveal processes underlying disease dynamics. Most prior work has assumed that age‐prevalence curves are shaped by infection rates, host immunity and/or infection‐induced mortality. Interactions between parasites within a host have largely been overlooked as a source of variation in age‐prevalence curves.We used field survey data and models to examine the role of interspecific interactions between parasites in shaping age‐prevalence curves. The empirical dataset included quantification of parasite infection prevalence for eight co‐occurring trematodes in over 15,000 snail hosts. We characterized age‐prevalence curves for each taxon, examined how they changed over space in relation to co‐occurring trematodes and tested whether the shape of the curves aligned with expectations for the frequencies of coinfections by two taxa in the same host. The models explored scenarios that included negative interspecific interactions between parasites, variation in the force‐of‐infection (FOI) and infection‐induced mortality that varied with host age, which were mechanisms hypothesized to be important in the empirical dataset.In the empirical dataset, four trematode parasites had monotonic increasing age‐prevalence curves and four had unimodal age‐prevalence curves. Some of the curves remained consistent in shape in relation to the prevalence of other potentially interacting trematodes, while some shifted from unimodal to monotonic increasing, suggesting release from negative interspecific interactions. The most common taxa with monotonic increasing curves had lower co‐infection frequencies than expected, suggesting they were competitively dominant. Taxa with unimodal curves had coinfection frequencies that were closer to those expected by chance.The model showed that negative interspecific interactions between parasites can cause a unimodal age‐prevalence curve in the subordinate taxon. Increases in the FOI and/or infection‐induced mortality of the dominant taxon cause shifts in the peak prevalence of the subordinate taxon to a younger host age. Infection‐induced mortality that increased with host age was the only scenario that caused a unimodal curve in the dominant taxon.Results indicated that negative interspecific interactions between parasites contributed to variation in the shape of age‐prevalence curves across parasite taxa and support the growing importance of incorporating interactions between parasites in explaining population‐level patterns of host infection over space and time. Read the freePlain Language Summaryfor this article on the Journal blog.
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- Award ID(s):
- 2129758
- PAR ID:
- 10578136
- Publisher / Repository:
- British Ecological Society
- Date Published:
- Journal Name:
- Functional Ecology
- Volume:
- 39
- Issue:
- 1
- ISSN:
- 0269-8463
- Page Range / eLocation ID:
- 91 to 102
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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