Hosts, pathogens, & hot ponds: Thermal mean and variability contribute to spatial patterns of chytrid infection

Abstract/Summary

Temperature is a key driver of heterogeneity in host–pathogen dynamics, but relatively little is known about how patch-scale temperature affects landscape-scale patterns of pathogen infection. Two hypotheses to relate to patch-scale thermal conditions to infection of ectothermic animals by fungal pathogens: (1) temperature variability tends to favor pathogens over hosts due to differences in acclimation; (2) higher mean temperatures can help hosts clear infections, owing to differences in thermal limits. We studied how patch-scale thermal conditions (mean and variability) affect infection of eastern newts Notophthalmus viridescens by Batrachochytrium dendrobatidis (Bd). We measured in situ temperature and Bd infection across 20 ponds in two years in southeastern Wisconsin, USA to (1) evaluate evidence against multiple thermal mediation hypotheses and (2) quantify whether among-site variation in thermal conditions drives patch-level heterogeneity in host–pathogen interactions. We found that (1) an index of thermal mean and variability was strongly and nonlinearly related to Bd infection and (2) among-pond differences in thermal conditions drove this relationship, highlighting that variation in patch-level conditions can drive heterogenous host–pathogen outcomes across landscapes. Our research collectively reveals insights about the importance of local, patch-level conditions for mediating disease risk at broader scales.