DOI: 10.5061/dryad.x3ffbg7vf
title: Age-prevalence curves in a multi-species parasite community

description: 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, 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
 force-of-infection 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.
description: See Preston et al. "Age-prevalence curves in a multi-species
 parasite community" in press at Functional Ecology for detailed
 methods on data collection. 
description: # Age-prevalence curves in a multi-species parasite community
 [https://doi.org/10.5061/dryad.x3ffbg7vf](https://doi.org/10.5061/dryad.x3ffbg7vf) ## Description of the data and file structure This dataset corresponds to 137 stream sites that were surveyed for Juga sp. snails and their trematode parasites in the Willamette Valley, Oregon, USA. ### Files and variables #### File: Snail\_Data\_Dryad.csv **Description:** Juga snail infection data from the Willamette Valley, Oregon, USA ##### Variables * site: the site identifier in the field survey * basin: the watershed the site exists in. LUCK = Luckiamute; SANT = Santiam; MCKZ = McKenzie; MRYS = Marys; MFW = Middle Fork Willamette; CFW = Coast Fork Willamette; WLMT MS = Willamette Mainstem * mean.per.snail.mass: the mean biomass (g) of Juga snails at that site * mean.snail.TL: the mean total shell length (mm) of Juga snails at that site * AOX.prev: the prevalence (% infected snails) of trematode with code "AOX"  * TLS.prev: the prevalence (% infected snails) of trematode with code "TLS"  * ES1.prev: the prevalence (% infected snails) of trematode with code "ES1"  * ES2.prev: the prevalence (% infected snails) of trematode with code "ES2"  * MR1.prev: the prevalence (% infected snails) of trematode with code "MR1"  * MR2.prev: the prevalence (% infected snails) of trematode with code "MR2"  * FT1.prev: the prevalence (% infected snails) of trematode with code "FT1"  * TP1.prev: the prevalence (% infected snails) of trematode with code "TP1"  ## Code/software Microsoft Excel