Environmentally transmitted parasites spend time in the abiotic environment, where they are subjected to a variety of stressors. Understanding how they face this challenge is essential if we are to understand how host-parasite interactions may vary across environmental gradients. We used a zooplankton-bacteria host-parasite system where availability of sunlight (solar radiation) influences disease dynamics to look for evidence of parasite local adaptation to sunlight exposure. We also examined how variation in sunlight tolerance among parasite strains impacted host reproduction. Parasite strains collected from clearer lakes (with greater sunlight penetration) were most tolerant of the negative impacts of sunlight exposure, suggesting local adaptation to sunlight conditions. This adaptation came with both a cost and a benefit for parasites: parasite strains from clearer lakes produced relatively fewer transmission stages (spores) but these strains were more infective. After experimental sunlight exposure, the most sunlight-tolerant parasite strains reduced host fecundity just as much as spores that were never exposed to sunlight. Sunlight availability varies greatly among lakes around the world. Our results suggest that the selective pressure sunlight exposure exerts on parasites may impact both parasite and host fitness, potentially driving variation in disease epidemics and host population dynamics across sunlight availability gradients. 

See manuscript methods for complete methodological information. 

Three data files include:

1) spore counts and numbers of offspring produced throughout the experiment for each Daphnia host individual

2) mean host offspring production and calculation of parasite transmission potential, based on data set 1

See metadata and manuscript methods for details on these calculations.

3) data corresponding with the online supplement showing infection (yes/no) and spore yields in clear or darkened containers in the laboratory portion of the experiment. See supplemental methods and metadata for more details. 

See metadata in Excel files (second tab)