Temperature-mediated shifts in salamander transcriptomic responses to the amphibian-killing fungus.

Life processes of ectothermic vertebrates are intimately linked to the temperature of their environment, influencing their metabolism, reproduction, behaviour and immune responses. In amphibians infected by the generalist chytrid pathogen Batrachochytrium dendrobatidis (Bd), host survival, infection prevalence and infection intensity are often temperature- and/or seasonally dependent. However, the transcriptional underpinnings of thermal differences in infection responses remain unknown. Measuring the impact of temperature on host responses to infection is a key component for understanding climatic influences on chytrid disease dynamics. The Bd-responsive gene pathways in frogs are well documented, but our understanding of salamander immune expression profiles during infection with chytrids remains limited. Here we characterize the transcriptomic responses of Plethodon cinereus using RNA sequencing by comparing skin and splenic gene expression of individuals uninfected, succumbing to Bd infection and naturally cleared of Bd infection at three temperatures. We suggest that amphibian temperature-dependent susceptibility to Bd is probably driven by shifts in expression of the innate and adaptive immune axes. Our study shows increased expression of transcripts associated with inflammation at lower temperatures and a shift towards increased expression of adaptive immune genes, including MHC (major histocompatibility complex), at higher temperatures. In the face of climate change, and as concerns for the spread of emergent chytrid pathogens increase, our results provide important functional genomic resources to help understand how these pathogenic fungi may continue to affect amphibian communities globally in the future.