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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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Parasites of the past: 90 years of change in parasitism for English sole
Historical data are extremely rare but essential for ascertaining whether contemporary infectious disease burdens are unusual. Natural history collections are a valuable source of such data, especially for reconstructing long timelines of parasite abundance. We quantified the parasites of 109 museum specimens of English sole (Parophrys vetulus), an economically important flatfish, collected from Puget Sound, Washington, over a 90‐year period (1930–2019). We counted nearly 2,500 individual parasites representing 23 distinct species/morphotypes and four broad taxonomic groupings. Of the 12 taxa that were prevalent enough to include in the analysis, nine did not change in abundance over time, two (an acanthocephalan and a trematode) decreased, and one (another trematode) increased. By broad taxonomic grouping, nematodes, trematodes, and leeches exhibited no change over time, whereas acanthocephalans declined significantly. The diverging patterns among parasite taxa suggest a double‐edged sword of responses to long‐term ocean change: some parasites might be on the rise, while others are declining.
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- Award ID(s):
- 1829509
- PAR ID:
- 10272110
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Frontiers in Ecology and the Environment
- Volume:
- 19
- Issue:
- 8
- ISSN:
- 1540-9295
- Page Range / eLocation ID:
- p. 470-477
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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