Physiological and evolutionary consequences of protein metabolism in Mytilus edulis L.

Rates of whole body protein turnover (WBPT) vary greatly in individual mussels (Mytilus edulis). These differences correlate with the heterozygosity of polymorphic enzyme loci and with aspects of individual physiological performance. Using a technique for the identification of individual proteins which account for the documented differences in rates of WBPT, this study has demonstrated a heterogeneity of turnover rates between individual proteins in mantle tissue. For some of these proteins, relative rates of turnover correlated with genotype and with aspects of physiological performance. The cellular stress response plays an important role in protection of organisms against the accumulation of abnormal proteins. Thermotolerance induced by elevated levels of endogenous cellular stress proteins seems to be especially significant in the seasonal adaptation of ectotherms. Endogenous levels of stress-70 proteins in mussels vary seasonally and correlate with seasonal changes in environmental temperature and with thermotolerance. These results indicate that environmental stress is sufficient to cause protein denaturation during a significant part of the year, and that high natural concentrations of stress-70 proteins promote thermotolerance. The exposure of M edulis to copper did not lead to significantly elevated levels of stress proteins, and copper tolerance was not effected by seasonal changes in temperature. The development of a gene probe for the measurement of hsp70 mRNA allowed differences in the accumulation of hsp70 mRNA to be observed between intertidal and subtidal M. edulis. These findings are relevant to the ways in which molecular changes in protein metabolism contribute to environmental adaptation in marine invertebrates, and hence have consequences for the ecological dynamics of these organisms