Temperature acclimatisation of swimming performance in the European Queen Scallop

The phenotypic plasticity of muscle performance and locomotory physiology allows the maintenance of essential activity capacity in the face of environmental change, and has been demonstrated in a wide phylogenetic range of eurythermal vertebrates. This study used the scallop, Aequipecten opercularis, as a model eurythermal invertebrate. Animals caught in different seasons demonstrated marked differences in their swimming performance and the relationship between, temperature and performance. When stimulated to swim at natural ranges of temperature, Winter (cold acclimatised), animals accelerated faster than autumn collected animals swimming at the same temperature (x 2 at 11degreesC) and attained higher velocities during jetting. The effects of acclimatisation were confined to the jetting phase and may be a mechanism for the maintenance of acceleration during predator-prey interactions. This is the first demonstration of the thermal acclimatisation of muscle performance in a mollusc and one of very few studies in invertebrates

Thermal sensitivity of mitochondrial function in the Antarctic Notothenioid, Lepidonotothen nudifrons

The thermal sensitivity of mitochondrial function was investigated in the stenothermal Antarctic fish Lepidonotothen nudifrons. State 3 respiration increases with increasing temperature between 0 °C and 18 °C with a Q 10 of 2.43–2.63. State 4 respiration in the presence of oligomycin, an inhibitor of mitochondrial ATP synthase, quantifies the leakage of protons through the inner mitochondrial membrane, which causes oxygen consumption without concomitant ATP production. This parameter shows an unusually high Q 10 of 4.21 ± 0.42 (0–18 °C), which indicates that proton leakage does not depend merely on ion diffusion but is an enzyme-catalysed process. The differential thermal sensitivity of oxidative phosphorylation (=state 3) and proton leakage (=state 4 in the presence of oligomycin) leads to progressive uncoupling of the mitochondria and decreased efficiency of oxidative phosphorylation under in vivo conditions if the body temperature of L. nudifrons increases

Mitochondrial function and critical temperature in the Antarctic bivalve, Laternula elliptica

Thermal sensitivities of maximum respiration and proton leakage were compared in gill mitochondria of the Antarctic bivalve Laternula elliptica for an assessment of the contribution of mitochondrial mechanisms to limiting temperature tolerance. Proton leakage was measured as the oxygen consumption rate during blockage of oxidative phosphorylation (state IV respiration + oligomycin). The maximum capacity of NADP dependent mitochondrial isocitrate dehydrogenase (IDH) was investigated as part of a proposed mitochondrial substrate cycle provoking proton leakage by the action of transhydrogenase. State III and IV + respiration rose exponentially with temperature. Thermal sensitivities of proton leakage and IDH were unusually high, in accordance with the hypothesis that H(+) leakage is an enzyme catalysed process with IDH being involved. In contrast to proton leakage, state III respiration exhibited an Arrhenius break temperature at 9 degrees C, visible as a drop in thermal sensitivity close to, but still above the critical temperature of the species (3-6 degrees C). Progressive uncoupling of mitochondria led to a drop in RCR values and P/O ratios at high temperature. The same discontinuity as for state III respiration was found for the activity of mitochondrial IDH suggesting that this enzyme may influence the thermal control of mitochondrial respiration. In general, the high thermal sensitivity of proton leakage may cause an excessive rise in mitochondrial oxygen demand and a decreased efficiency of oxidative phosphorylation. This may exceed the whole animal capacity of oxygen uptake and distribution by ventilation and circulation and set a thermal limit, characterized by the transition to anaerobic metabolism. (C) 1999 Elsevier Science Inc. All rights reserve