Elevated temperatures dampen the innate immune capacity of developing lake sturgeon (Acipenser fulvescens).

Abstract

Chronic exposure to high temperatures may leave freshwater fishes vulnerable to opportunistic pathogens, particularly during early life stages. Lake sturgeon, Acipenser fulvescens, populations within the northern expanse of their range in Manitoba, Canada, may be susceptible to high temperature stress and pathogenic infection. We acclimated developing lake sturgeon for 21 days to two ecologically-relevant, summer temperatures (16 and 20°C). Individuals from both acclimation treatments were then exposed to 0, 30, and 60 µg.ml-1 bacterial lipopolysaccharides (endotoxins), as an immune stimulus, for 48 h and sampled 4 and 48 h during trial exposures and following a 7-day recovery period. We then measured whole body transcriptional (mRNA) responses involved in the innate immune, stress, and fatty acid responses following acute exposure to the bacterial endotoxins. Data revealed that overall levels of mRNA transcript abundance were higher in 20°C reared sturgeon under control conditions. However, following exposure to a bacterial stimulus, lake sturgeon acclimated to 16°C produced a more robust and persistent transcriptional response with higher mRNA transcript abundance across innate immune, stress, and fatty acid responses than their 20°C acclimated counterparts. Additional whole-animal performance metrics (critical thermal maximum, metabolic rate, cortisol concentration, and whole-body and mucosal lysozyme activity) demonstrated acclimation-specific responses, indicating compromised metabolic, stress, and enzymatic capacity following the initiation of immune related responses. Our study showed that acclimation to 20°C during early development impaired the immune capacity of developing lake sturgeon as well as the activation of molecular pathways involved in the immune, stress, and fatty acid responses. The present study highlights the effects of ecologically-relevant, chronic thermal stress on seasonal pathogen susceptibility in this endangered species.