Acclimation capacity of the cardiac HSP70 and HSP90 response to thermal stress in lake trout (Salvelinus namaycush), a stenothermal ice-age relict.

The ability of cold-adapted species to persist in the face of climate change will depend on the capacity of individuals for thermal acclimation, adaptation, and the degree of physiological variation that exists among populations. We tested the acclimation capacity of cardiac HSP70 and HSP90 in four populations of lake trout (Salvelinus namaycush), a cold-adapted salmonid. We acclimated fish to four temperatures (8°C, 11°C, 15°C, and 19°C) and measured cardiac HSP70 and HSP90 levels by western blot prior to and following an acute (1h) heat shock at 23°C. Basal and induced cardiac HSP70 and HSP90 expression was similar among lake trout populations. Induced cardiac HSP70 was significantly lower in heat-shocked lake trout acclimated to 19°C compared to all other temperatures. Acclimation temperature had no significant effect on cardiac HSP90 prior to heat shock (control HSP90) and a significant effect on HSP90 in heat-shocked fish, although most significant treatment comparisons were marginal. However, for warm-acclimated fish (15°C and 19°C), cardiac HSP90 levels were lower in heat-shocked versus control fish. Together, this suggests that the induction temperature of cardiac HSP synthesis may increase with warm acclimation in lake trout. This plasticity in the cardiac HSR could assist lake trout populations in coping with longer periods of thermal stress as predicted by climate change models. The cardiac HSR supports previous research suggesting lake trout thermal physiology may be conserved across a wide geographic range.