Effects of temperature on specific dynamic action and protein synthesis rates in the Baltic isopod crustacean, Saduria entomon

The mean rate of oxygen consumption in fasted Saduriaentomon increased between 4°C and 13°C with a Q10 of 2.33. After feeding, rates of oxygen uptake increased significantly by two- to threefold at both temperatures. However, the magnitude of the ‘specific dynamic action of food’ (SDA) response varied with temperature. At 4°C, the magnitude was 45.5±4.2 μmol, while at 13°C, magnitude was significantly higher at 62.8±6.5 μmol. In contrast, the duration of the response did not vary significantly with temperature in Saduria, with the consequence that the duration at 4°C was considerably shorter than that measured at this temperature from an Antarctic isopod in a parallel study, and the duration at 13°C was considerably longer than published values for temperate crustaceans at similar temperatures. Fasted rates of ammonia excretion increased with a Q10 of 4.74 between 4°C and 13°C. The increase after feeding was sevenfold at 4°C but only 2.6-fold at 13°C. Fasted O/N ratios for Saduria at 4°C were about twice those at 13°C. Fasted whole body protein synthesis rates (kS) increased with a Q10 of 2.61 between 4°C and 13°C. Whole body kS, measured at the peak of the SDA response, showed significant 2.7-and 1.9-fold increases at 4°C and 13°C, respectively, compared to fasted values, although the factorial rise at 13°C was reduced compared to 4°C. Alterations in kS rates after feeding at both temperatures resulted from significant increases in RNA activity (KRNA) alone. However, the increase in kS between 4°C and 13°C was accompanied by increases in both KRNA and RNA/protein ratio, a measure of the capacity for protein synthesis (CS).