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ABSTRACT Wild populations face unprecedented pressure from an assortment of anthropogenic environmental changes and parasites. We sought to understand how host–parasite interactions are affected by the interactive effects of multiple environmental stressors and subsequent parasite infection.We focused on American bullfrog tadpoles (Lithobates catesbeianus) that can become infected by several parasite species (e.g., trematodes in the family Echinostomatidae genus Echinstoma, andBatrachochytrium dendrobatidis; “Bd”) and are affected by abiotic stressors including road salt and variable temperatures attributed to climate change. In a multi‐phase laboratory experiment, we exposed tadpoles to one of two salt treatments (0 and 1.5 g L−1added NaCl sublethal salt) and one of two temperature treatments (constant 23°C and fluctuating between 20°C and 25°C). Next, we exposed these tadpoles to one of four parasite treatments (parasite absent,Bdonly, trematodes only, andBd& trematodes together) at a constant temperature (23°C) without added salt. We then recorded morphological measurements (length, mass, developmental stage) and quantified infection intensity.Tadpoles exposed toBdwere larger in mass than the other parasite treatments, and the effects of trematode exposure on length varied by temperature. We did not detect any effect of our treatments on developmental stage. We found an interaction between the salinity and temperature treatments where tadpoles exposed toBdonly or to fluctuating temperatures andBdand trematodes together had higherBdinfection in the no salt added treatment compared to the sublethal salt treatment. Tadpoles in stable temperatures and no salt treatments had lower subsequentBdinfection loads than those in stable temperatures and elevated salt. With trematode infection, we found that when no salt was added, tadpoles exposed to trematodes only had higher parasite abundance compared to the other treatments (i.e., a salinity by parasite interaction).Our results suggest that the interaction of temperatures and salt pollution in freshwater can increase subsequentBdinfection and that the parasites (Bd& echinostome trematodes) can interact with each other, altering infection levels.
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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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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1111/1365-2435.14701
