Can hot temperatures limit disease transmission? a test of mechanisms in a zooplankton-fungus system

1. Thermal ecology theory predicts that transmission of infectious diseases should respond unimodally to temperature, i.e., be maximized at intermediate temperatures and constrained at extreme low and high temperatures. However, empirical evidence linking hot temperatures to decreased transmission in nature remains limited.2. We tested the hypothesis that hot temperatures constrain transmission in a zooplankton-fungus
(Daphnia dentifera-Metschnikowia bicuspidata) disease system where autumnal epidemics typically start after lakes cool from their peak summer temperatures. This pattern suggested that maximally hot summer temperatures could be inhibiting disease spread. 3. Using a series of lab experiments, we examined the effects of high temperatures on five mechanistic components of transmission. We found that (1) high temperatures increased exposure to parasites by speeding up foraging rate but (2) did not alter infection success post-exposure. (3) High temperatures lowered parasite p...