Temperature Influences Whole‐Animal Rates of Metabolism but Not Protein Synthesis in a Temperate Intertidal Isopod

The effects of temperature on two important biological rate processes, whole-body rates of oxygen uptake (M dot o2) and protein synthesis (k(s)), were investigated in the temperate intertidal isopod Ligia oceanica at two different times of the year. Animals were collected in January (winter) and June (summer) and either subjected to an acute temperature change after 24 h (acclimatized) or acclimated to various temperatures for 4 wk. In both cases, M dot o2 increased with temperature, with a Q(10) of 2.2 between 5 degrees and 20 degrees C, but increased in thermal sensitivity at 25 degrees C. Winter isopods were characterized by significantly higher M dot o2 levels, greater thermal sensitivities, and lower thermal tolerances than summer animals. Seasonal differences in M dot o2 persisted after acclimation, indicating that temperature alone was not responsible for the changes. In sharp contrast, whole-body k(s) showed no variation with temperature, although overall rates decreased upon acclimation. In acclimatized animals, k(s) was higher in the summer than in the winter. After acclimation, a compensatory increase in RNA capacity in winter animals reversed this situation. The temperature independence of whole-body k(s) in L. oceanica could ensure survival in a highly liable thermal environment, as thermal tolerances of intertidal invertebrates are thought to be more closely related to protein than to energy metabolism.