DOI: 10.5061/dryad.p7507
title: Data from: Poor resource quality lowers transmission potential by changing foraging behaviour

description: Resource quality can have conflicting effects on the spread of disease.
 High quality resources could hinder disease spread by promoting host
 immune function. Alternatively, high quality food might enhance the spread
 of disease through other traits of hosts or parasites. Thus, to assess how
 resource quality shapes epidemics, we need to delineate mechanisms by
 which food quality affects key epidemiological traits. Here, we
 disentangle effects of food quality on ‘transmission potential’ – a key
 component of parasite fitness that combines transmission rate and parasite
 production – using a zooplankton host and fungal parasite. We estimated
 the components of transmission potential (i.e., parasite encounter rate,
 susceptibility, and yield of parasite propagules) for hosts fed a high
 quality green alga and a low quality cyanobacterium. A focal experiment
 was designed to disentangle food quality effects on various components of
 transmission potential. The low quality resource decreased transmission
 potential by stunting host growth and altering foraging behaviour. Hosts
 reared on low quality food were smaller and had lower size-corrected
 feeding rates. Due to their slower grazing, they encountered fewer
 parasite spores in the water. Smaller hosts also had lower risk of an
 ingested spore causing infection (i.e., lower susceptibility), and yielded
 fewer parasite propagules. Hosts switched from high to low quality food
 during spore exposure also had low transmission potential – despite their
 large size – because the poor quality resource strongly depressed
 foraging. A follow-up experiment investigated traits of the low quality
 resource that might have driven those results. Cyanobacterial compounds
 that can inhibit digestive proteases of a related grazer likely did not
 cause the observed reductions in transmission potential. Our study
 highlights the value of using mechanistic models to pinpoint how resource
 quality can change transmission potential. Overall, our results show that
 low quality resources could inhibit the spread of disease through effects
 on multiple components of transmission potential. They also provide
 insight into how disease outbreaks in wildlife may respond to shifts in
 resource quality caused by eutrophication or climate change.
description: Data from the infection
 assay and feeding rate assay in the first experiment.The transmission model
 (equ. S1 and S2) and foraging model (equ. S4) were simultaneously fit to
 these data from the infection and feeding rate assays, respectively. For
 more details on how these data were used to estimate components of
 transmission potential, see 'Statistical methods for estimating
 parameters' in Appendix S1.First_Experiment.xlsxData from the infection assay in the second experiment.The transmission model (equ. S1 and S2) was fit to these data to estimate infection risk. For more details on how these data were used to estimate components of transmission potential, see 'Statistical methods for estimating parameters' in Appendix S1.Second_Experiment.xlsx