Heat-Shock Protein Expression in Mytilus californianus: Acclimatization (Seasonal and Tidal-Height Comparisons) and Acclimation Effects

Heat-shock protein (hsp) expression was examined in gill of field-acclimatized and laboratory-acclimated mussels (Mytilus californianus) from the Oregon coast. Endogenous levels of heat-shock proteins in the 70-kDa class (hsp70 isoforms) and profiles of induction temperature for newly synthesized hsp70 were measured in freshly field-collected specimens as functions of location height in the intertidal and season, and in mussels after 7 weeks of laboratory thermal acclimation. There were significant differences in endogenous levels of hsp70 as functions of season and collection height. Strong induction of new hsp70 synthesis occurred at body temperatures within the range measured in field specimens. Profiles of hsp70 thermal induction varied significantly with season, but not with height of collection. In contrast to the large differences in hsp70 expression between winter- and summer-acclimatized mussels, no differences related to temperature occurred in the differently acclimated mussels. The differences found between the effects of field acclimatization and laboratory thermal acclimation suggest that the stress response is modulated by environmental factors in addition to body temperature. Thus, caution is required in extrapolating from laboratory acclimation studies to acclimatization effects in field populations. The seasonal and tidal-height variations in the heat-shock response are discussed in the context of energy costs of protein turnover.