Is metabolic rate depression (MRD) a life prolonging strategy in long-lived Arctica islandica on a latitudinal climate gradient? Environmental constraints and evolutionary adaptation in the Ocean quahog

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The ocean quahog Arctica islandica is an arctic boreal marine mud clam with a wide ranging distribution on the Northern hemisphere, spanning habitats with different climate regimes. It is also the longest-lived of all bivalve and molluscan species, animals >100 yrs are common in many populations, and reported maximum live span is 374 yrs (Iceland population). However, such venerable age has not yet been reported for all populations. Based on the Free Radical-Rate of Living theory by Pearl (1928) and Harman (1956) we assume that random bouts of self-induced metabolic rate depression (MRD) will lower generation rates of reactive oxygen species. This may be an energy saving and life prolonging strategy in the ocean quahog. Further, we assume that cold climate will favour MRD behaviour and raise life expectancy in cold-boreal compared to temperate populations.Here we propose to study MRD behaviour in two A. islandica populations from different temperature regimes (Iceland and North Sea) in an age dependent manner. We will compare postmitotic neuronal and proliferating tissues (gill, mantle, adductor muscle) of differently aged individuals from the two populations with respect to energy metabolism, antioxidant capacities, oxidative stress indicators and lipofuscin accumulation. Physiological age and stress markers will be related to MRD frequency and duration in both populations. Moreover, we propose to investigate the involvement of an NO signal in MRD during self-induced hypoxic/anoxic exposure of the quahog.