The Onset Temperature of the Heat-Shock Response and Whole-Organism Thermal Tolerance Are Tightly Correlated in both Laboratory-Acclimated and Field-Acclimatized Tidepool Sculpins (Oligocottus maculosus)

We examined the relationship between thermal tolerance, measured as critical thermal maximum (CTmax), and aspects of the heat-shock response in tidepool sculpins (Oligocottus maculosus) acclimated to constant laboratory temperatures or acclimatized to field conditions. The CTmax of fish laboratory acclimated to 6 degrees, 13 degrees, and 20 degrees C were 27.6 degrees +/- 0.1 degrees C, 29.5 degrees +/- 0.1 degrees C, and 30.8 degrees +/- 0.1 degrees C, respectively, increasing linearly by 0.2 degrees C for each 1 degrees C increase in acclimation temperature. The CTmax of field-acclimatized fish from the low intertidal (29.9 degrees +/- 0.1 degrees C) was significantly lower than that of fish from the mid- (30.5 degrees +/- 0.1 degrees C) and high (30.4 +/- 0.1 degrees C) intertidal. CTmax and the onset temperature of hsp70 induction in gill (T-on) were highly correlated in both laboratory-acclimated and field-acclimatized sculpins, with T-on occurring at 2 degrees C below CTmax in all cases. However, there was no consistent relationship between CTmax and the maximum levels of gill hsp70 mRNA. Predicted acclimation temperature (15.9 degrees +/- 0.5 degrees C) and mean habitat temperature (15.9 degrees +/- 1.6 degrees C) were similar for sculpins from low intertidal pools, but this relationship was not apparent in mid-and high intertidal fish. Mark-recapture experiments indicated that approximately 80% of fish from low intertidal pools were residents of that pool, but residency rates were less than 50% in mid-and high intertidal pools, which may explain the lack of correlation between CTmax and habitat variables in these groups. These data indicate that gill hsp70 T-on and CTmax are highly correlated indicators of the thermal performance of tidepool sculpins in both laboratory and field settings.