The influence of acclimation on the organismal and molecular thermotolerance parameters in two Arctic teleosts

Abstract

The nearshore Beaufort Sea is a highly dynamic thermal environment that is faced with climate change-driven increases in temperature. Analyzing the thermotolerance of important Arctic subsistence and prey fishes, such as broad whitefish Coregonus nasus and saffron cod Eleginus gracilis, will provide an understanding of the relative species specific responses to current and future temperature changes. The objectives of this study were to determine if acclimating broad whitefish and saffron cod to two different temperatures (5 and 15°C) affected their critical thermal maximum (CTmax) and their HSP70 protein and mRNA transcript concentrations in brain, muscle, and liver tissues. Following acclimation, fish were exposed to a thermal ramping rate of 3.4°C · h-¹. The CTmax temperature was recorded when the fish expressed a loss of equilibrium. Tissue samples were then collected and analyzed via western blotting and transcriptome sequencing. Broad whitefish and saffron cod acclimated to 15°C had a significantly higher mean CTmax (27.3°C and 25.9°C, respectively) than 5°C fish (23.7°C and 23.2°C, respectively). Broad whitefish had a significantly higher CTmax than saffron cod at 15°C in addition to significantly higher HSP70 protein concentrations in liver and muscle tissues at both acclimation temperatures. Brain and muscle tissues had the highest and lowest HSP70 protein concentrations, respectively, for both species and acclimation temperatures. The only significant difference in protein concentration between acclimation temperatures was in saffron cod liver tissues where 5°C samples had a significantly higher concentration than 15°C. Brain and liver tissues for broad whitefish acclimated to 15°C had significantly higher HSP70 mRNA transcript concentrations than the control group that remained in lab-acclimation conditions of 8°C. Transcript B expressed a higher quantity of transcripts than transcript A, but both transcripts followed similar expression profiles and there were no differences in transcript concentration between tissues. The molecular data from this study demonstrates the cellular mechanisms that are, in part, responsible for the observed shifts in broad whitefish and saffron cod organismal thermotolerance, and this elasticity could be used to respond to changing thermal conditions in the nearshore Beaufort Sea in the future.