Temperature-dependent changes to host-parasite interactions alter the thermal performance of a bacterial host

Abstract Thermal performance curves (TPCs) are used to predict changes in species interactions, and hence range shifts, disease dynamics and community composition, under forecasted climate change. Species interactions might in turn affect TPCs. Here, we investigate whether temperature-dependent changes in a microbial host-parasite interaction (the bacterium Pseudomonas fluorescens , and its bacteriophage, SBWФ2) changes the host TPC. The bacteriophage had a narrower infectivity range, with their critical thermal maximum ∼6°C lower than those at which the bacteria still had high growth. Consequently, in the presence of phage, the host TPC had a higher optimum temperature and a lower maximum growth rate. These changes were driven by a temperature-dependent evolution, and cost, of resistance; the largest cost of resistance occurring where bacteria grew best in the absence of phage. Our work highlights how ecological and evolutionary mechanisms can alter the effect of a parasite on host thermal performance, even over very short timescales. Data accessibility statement All data and R code used in the analysis will be made available on GitHub and archived on Zenodo.