SEASONAL-CHANGES IN STRESS-70 PROTEIN-LEVELS REFLECT THERMAL TOLERANCE IN THE MARINE BIVALVE MYTILUS-EDULIS L

Fluctuating concentrations of cellular stress proteins may be especial ly significant in the environmental adaptation of eurythermal ectother ms. This study has demonstrated that endogenous levels of stress-70 pr oteins in M. edulis vary seasonally and are positively correlated with seasonal changes both in environmental temperature and thermal tolera nce. The levels of stress-70 protein isoforms of 70, 72 and 78 kDa wer e analyzed in M. edulis L. collected at six consecutive bimonthly inte rvals from the River Exe (Devon, UK). Significant seasonal differences in endogenous levels of the stress-70 proteins in M. edulis were obse rved. Levels of these protein isoforms correlated positively with seas onal changes in environmental temperature. Levels of the 70 kDa protei n showed a larger seasonal variation, more closely related to natural temperature change, than levels of the 72 and 78 kDa proteins. Additio nal mussels from the same samples were heat-stressed at 28.5 degrees C , a temperature at which M. edulis is unable to acclimate. M. edulis s urvived longer at 28.5 degrees C during the warmer months of the year. There were also positive correlations between time of survival at 28. 5 degrees C and the coincident levels of endogenous stress-70 proteins . Our results provide evidence that environmental stress may have been sufficient to cause at least partial protein denaturation during a si gnificant proportion of the year, and suggest that high natural concen trations of stress-70 proteins may promote thermal tolerance. Evidence from other studies suggests that maintaining high levels of stress pr oteins have significant energetic costs and may be detrimental to orga nismal fitness. We discuss our findings in terms of the costs and bene fits associated with stress protein synthesis, and consequences for th e ecology and distribution of marine ectotherms. (C) 1998 Elsevier Sci ence B.V. All rights reserved.