How does oxidative stress relate to thermal tolerance in the Antarctic bivalve Yoldia eightsi?

Short and long-term exposure to elevated temperatures were studied in the A ntarctic stenothermal protobranch bivalve Yoldia eightsi (Courthouy) from P otter Cove, King George Island (South Shetland Islands, Antarctica). Above a breakpoint temperature of 2 degreesC - the upper habitat temperature for the Potter Cove Y eightsi stock - both routine (RMR) and standard metabolic rate (SMR) increased steeply. The fraction of metabolism allocated to SMR, as well as the number of intervals of elevated activity per hour increased significantly-with temperature. During acute exposure, ATP concentrations in the foot muscle peaked at 2 degreesC and fell at 5 degreesC, whereas sup eroxide dismutase (SOD) activity decreased upon warming. Slow stepwise warm ing to a final temperature of 11 degreesC resulted in a significant decreas e of SOD activity. Malondialdehyde concentration increased compared with co ntrols at 0 degreesC. In contrast to the effect of short-term exposure, tis sue adenylate concentrations displayed a mild increase at higher temperatur es during slow warming, indicating an acclimation response. A switch to ana erobic energy production could not be observed up to 11 degreesC, demonstra ting a higher level of thermal tolerance than in other Antarctic ectotherms , or a failure of the relevant pathways in Y eightsi. The imbalance between pro- and antioxidant processes upon warming indicate oxidative stress to b e one feature accompanying early heat stress in Y eightsi.