Effects of acclimation temperature on the thermal physiology in two geographically distinct populations of lake sturgeon ().

Temperature is one of the most important abiotic factors regulating development and biological processes in ectotherms. By 2050, climate change may result in temperature increases of 2.1-3.4°C in Manitoba, Canada. Lake sturgeon, , from both northern and southern populations in Manitoba were acclimated to 16, 20 and 24°C for 30 days, after which critical thermal maximum (CT) trials were conducted to investigate their thermal plasticity. We also examined the effects of temperature on morphological and physiological indices. Acclimation temperature significantly influenced the CT, body mass, hepatosomatic index, metabolic rate and the mRNA expression of transcripts involved in the cellular response to heat shock and hypoxia (, , , ) in the gill of lake sturgeon. Population significantly affected the above phenotypes, as well as the mRNA expression of -α1 and the hepatic glutathione peroxidase enzyme activity. The southern population had an average CT that was 0.71 and 0.45°C higher than the northern population at 20 and 24°C, respectively. Immediately following CT trials, mRNA expression of and was positively correlated with individual CT of lake sturgeon across acclimation treatments and populations ( = 0.7,  = 0.62, respectively;  < 0.0001). Lake sturgeon acclimated to 20 and 24°C had decreased hepatosomatic indices (93 and 244% reduction, respectively;  < 0.0001) and metabolic suppression (27.7 and 42.1% reduction, respectively;  < 0.05) when compared to sturgeon acclimated to 16°C, regardless of population. Glutathione peroxidase activity and mRNA expression -α1 were elevated in the northern relative to the southern population. Acclimation to 24°C also induced mortality in both populations when compared to sturgeon acclimated to 16 and 20°C. Thus, increased temperatures have wide-ranging population-specific physiological consequences for lake sturgeon across biological levels of organization.