Physiological ageing in a polar and a temperate swimming scallop

We compared physiological ageing parameters in 2 scallops, the temperate Aequipecten opercularis and the Antarctic Adamussium colbecki. These 2 species are phylogenetically closely related and display a similar lifestyle but have distinctly different maximum lifespans (MLSP). A. opercularis does not live longer than 8 to 10 yr, whereas A. colbecki lives over 18 yr. The development of several physiological ageing parameters over time, chosen according to the ‘free radical theory of ageing‘, was compared in the 2 species to identify differences in the ageing process. In the shorter-lived A. opercularis, activities of the mitochondrial enzymes citrate synthase and cytochrome c oxidase and of the antioxidant enzyme catalase showed a more pronounced decrease with increasing age than in the longer-lived A. colbecki. In line with this finding, lipofuscin accumulation increased more distinctly in A. opercularis than in A. colbecki, while tissue protein content decreased in A. opercularis but increased in A. colbecki. Its better preservation of mitochondrial and antioxidant enzyme activities and the avoidance of waste accumulation may enable A. colbecki to live longer than A. opercularis. Mitochondrial function investigated in A. opercularis showed only minor changes with age, and mitochondrial H2O2 generation rates were low at all ages. We relate our findings to the ‘free radical–rate of living’ theory, to the ‘uncoupling to survive‘ hypothesis, and to the particular lifestyle of these scallops

In vitro protein synthesis capacities in a cold stenothermal and a temperate eurythermal pectinid

The translational system was isolated from the gills of the Antarctic scallop Adamussium colbecki (Smith) and the European scallop Aequipecten opercularis (Linnaeus) for in vitro protein synthesis capacities (g protein mg FW–1 day–1) and the translational capacities of RNA (kRNA in vitro mg protein mg RNA–1 day–1). In vitro protein synthesis capacity in the cold-adapted pectinid at 0 °C was similar to the one found in the temperate scallop at 25 °C. These findings might reflect cold compensated rates in Adamussium colbecki, partly explainable by high tissue levels of RNA. Cold-compensated in vitro protein synthesis capacities may further result from increments in the translational capacity of RNA. The thermal sensitivity of the translation machinery was slightly different in the two species, with significantly lower levels of Arrhenius activation energies Ea and Q10 in Adamussium colbecki in the temperature range 0–15 °C. Reduced protein synthesis and translational capacities were found in vitro in gills of long-term aquarium-maintained Adamussium colbecki and were accounted for by a loss of protein synthesis machinery, i.e. a reduction in RNA levels, as well as a decrease in the amount of protein synthesized per milligram of RNA (RNA translational capacity, kRNA in vitro). Such changes may involve food uptake or mirror metabolic depression strategies, like those occurring during winter. Consequences of high in vitro RNA translational capacities found in the permanently cold-adapted species are discussed in the context of seasonal food availability and growth rates at high latitudes

Squid (Lolliguncula brevis) life in shallow waters: oxygen limitation of metabolism and swimming performance

Squid (Lolliguncula brevis) were exercised in a tunnel respirometer during a stepwise increase in water velocity in order to evaluate the anaerobic treshold, i.e. the critical swimming speed above which anaerobic metabolism contributes to energy production. The average anaerobic treshold was found at speeds of 1.5-2 mantle lenghts s-1. Above this velocity, α-glycerophosphate, succinate and levels fell and phospho-L-arginine was progressively depleted, while the levels of glucose 6-phosphate and inorganic phosphate rose. The finding of a simultaneous onset of anaerobic metabolism in the cytosol and the mitochondria indicates that a limited oxygen supply to the mitochondria elicits anaerobic energy production. This finding is opposite to the situation found in many other vertebrate and invertebrate species, in which energy covered by anaerobic energy production. This finding is opposite to the situation found in many other vertebrate and invertebrate species, in which energy requirements in exvess of aerobic energy production are covered by anaerobic metabolism, with mitochondira remaining aerobic. In L. brevis, swimming at higher speeds is associated with a small factorial increase in metabolic rate based on a high resting rate of oxygen cnsumption. Pressure recordings in the mantle cavity support this finding, indicating a high basal level of spontaneous activity at rest and a small rise in mean pressure at higher swimming velocity. Bursts of higher pressures from the jet support elevated swiming speeds and may explain the early transition to anaerobic energy production which occurs when pressure rises above 0.22-0.25kPa. The finding f mitochondrial hypoxia at a low critical speed in these squid is interpreted to be related to their life in shallow coastal and bay waters, which limits the necessity to maintain high swimming velocities. At increased swimming velocities, the animals oscilliate between periods of high and lo muscular activity. This behaviour is interpreted to reduce transport cost and to permit a longer-term net use of anaerobic resources when speed exceeds the critical value or when the squid dive into toxic waters. The simultaneous onset of anaerobic metabolism in the cytosol and the mitochondria emphasizes that squid generally make maximal use of available requirements are the highest among marine invertebrates