The effects of temperature on metabolic rate and protein synthesis following a meal in the isopod Glyptonotus antarcticus, Eights (1852)
Seawater temperatures in Antarctica are low, and typically rather stable seasonally. Associated with this, many marine invertebrates have low resting metabolic rates with a limited aerobic scope, and are often stenothermal. We have therefore investigated the response of metabolic rate and protein synthesis to feeding in the large Antarctic isopod, Glyptonotus antarcticus, at two different temperatures. The resting oxygen consumption of starved Glyptonotus was low, and comparable with a previous measure for this species and other Antarctic marine invertebrates. Resting metabolic rate exhibited a Q10 of 2.18 between 0°C and +4°C. After feeding at 0°C, oxygen consumption increased by a factor of 2.5 and ammonia excretion eightfold, before returning to prefeeding levels, in a classic if somewhat prolonged SDA (specific dynamic action) response. At 4°C, the postprandial factorial increase in both oxygen uptake and ammonia excretion was reduced. Whole-body protein synthesis rates for prefeeding animals showed a similar Q10 to oxygen consumption. Rates of synthesis increased significantly after feeding, and there was an associated drop in the O:N ratio, indicating that protein formed the primary metabolic substrate during the SDA response. The contribution of the costs of protein synthesis to the overall SDA was estimated to be 68%, although this estimate is based on a previous estimate of the costs of protein synthesis in Glyptonotus which is higher than typical values for temperate-water crustaceans. The fraction of ingested energy utilised in the SDA was, however, low (2-3%). Further work is needed to determine whether these unusual features in Glyptonotus are typical of polar marine invertebrates in general.