Elevated temperatures dampen innate immune responses of developing lake sturgeon (Acipenser fulvescens) when challenged with bacterial lipopolysaccharides

Abstract

Chronic temperature stress 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 thermal stress. We acclimated developing lake sturgeon for 21 days to two ecologically relevant temperatures (16 and 20oC) . Both acclimation treatments were exposed to 0, 30, and 60 µg.ml-1 bacterial lipopolysaccharides (endotoxins), as an immune stimulus, for 48 hr, with samples taken 4 and 48 hr during trial exposures and following a 7-day recovery period. We then measured whole body transcriptional (mRNA) and physiological (lysozyme activity, cortisol, glucose) responses involved in the innate immune, general stress, and fatty acid responses following acute exposure to bacterial endotoxins. Data detailing the responses involved in the above physiological processes revealed that while overall expression levels were higher at 20oC under control conditions, during bacterial stimulus 16oC reared lake sturgeon produced a more robust response with higher induced expression of the above responses than their 20oC acclimated counterparts. Additional whole-animal performance metrics (critical thermal maximum and metabolic rate) demonstrated acclimation-specific responses indicating compromised metabolic capacity following the initiation of immune related responses. Our study showed that acclimation to 20oC during early development impaired the activation of molecular pathways involved in the immune, stress, and fatty acid responses of lake sturgeon, highlighting the effects of chronic thermal stress on transcriptional activation and recruitment of downstream biological processes in this critically threatened and endangered species.