Temperature and host diet jointly influence the outcome of infection in a Daphnia‐fungal parasite system

Abstract

Climate change has the potential to shape the future of infectious diseases, both directly and indirectly. In aquatic systems, for example, elevated temperatures can modulate the infectivity of waterborne parasites and affect the immune response of zooplanktonic hosts. Moreover, lake warming causes shifts in the communities of primary producers towards cyanobacterial dominance, thus lowering the quality of zooplankton diet. This may further affect host fitness, resulting in suboptimal resources available for parasite growth. Previous experimental studies have demonstrated the respective effects of temperature and host diet on infection outcomes, using the zooplankter Daphnia and its microparasites as model systems. Although cyanobacteria blooms and heat waves are concurrent events in nature, few attempts have been made to combine both stressors in experimental settings. Here, we raised the zooplankter Daphnia (two genotypes) under a full factorial design with varying levels of temperature (the standard 19°C and elevated 23°C), food quality (Scenedesmus obliquus as high‐quality green algae, Microcystis aeruginosa and Planktothrix agardhii as low‐quality cyanobacteria) and exposed them to the parasitic yeast Metschnikowia bicuspidata. We recorded life history parameters of the host as well as parasite traits related to transmission. The combination of low‐quality cyanobacterial diets and elevated temperature resulted in additive detrimental effects on host fecundity. Low‐quality diets reduced parasite output, while temperature effects were context dependent. Overall, we argue that the combined effects of elevated water temperature and poor‐quality diets may decrease epidemics of a common fungal parasite under a climate change scenario.

Temperature and pathogen exposure act independently to drive host phenotypic trajectories

“…Increases in temperature and pathogen exposure, however, will not only shape host thermal tolerance, but will also drive changes in all aspects of a host's phenotype, including development, growth, fecundity and population-level processes (e.g. [9,[14][15][16][17]). Population persistence will therefore be shaped by how temperature change and pathogen exposure directly interact to shift multiple facets of a host's phenotype, in addition to the complex role that temperate plays in driving pathogen transmission strategies [18][19][20] and host-pathogen interactions more broadly [21,22].…”

“…Studies of the impacts of temperature and pathogen exposure often focus on their effects on individual host traits (e.g. [14][15][16][17]). However, organisms are comprised of multiple correlated traits that together form the integrated phenotype [26].…”

Transcriptomic response of Daphnia magna to nitrogen‐ or phosphorus‐limited diet

“…A recent study showed that low‐quality diet (cyanobacteria) could reduce the output of Daphnia gut parasites (Manzi et al., 2020 ). Besides, food with high C:P ratios can significantly reduce bacterial infection rates in daphnids (Frost et al., 2008 ).…”

“…A recent study showed that low-quality diet (cyanobacteria) could reduce the output of Daphnia gut parasites (Manzi et al, 2020).…”

Transcriptomic Response of Daphnia Magna to Nitrogen or Phosphorus Limited Diet

“…A recent study showed that low-quality diet (cyanobacteria) could reduce the output of Daphnia gut parasites [30]. Besides, food with high C : P ratios can signi cantly reduce bacterial infection rates in daphnids [31].…”