Using bomb calorimetry to assess thermal and seasonal energetics

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Many overwintering ectotherms pass the winter 'trapped' beneath the ice-cover of ponds.  During the early stages of their cold submergence, their metabolic rate is lowered by the cold temperatures.  As winter proceeds, the oxygen consumption of the residents in the pond and decaying vegetation effectively 'outpaces' the amount of oxygen renewed through photosynthesis, thus reducing the oxygen levels (i.e., become hypoxic).  The overwintering animal is placed in a precarious situation where it must not only cope with the dwindling oxygen, but also with a finite supply of energy stores (primarily fats and carbohydrates).  In the laboratory, these animals burn fat stores at the beginning of winter and turn to carbohydrate stores as cold, hypoxic exposure progresses, presumably sparing fat stores for spring activities.  How and whether these relationships manifest in the field is unknown.  Overwintering is accompanied quite often by large winterkill in the spring, where high numbers of aquatic ectotherms (mainly amphibians and fish) succumb to the combined cold and hypoxic environments.  Those that survive these conditions are presumably depleted of energy stores; yet, many amphibians must engage immediately in costly spring reproductive behaviours upon emergence from their overwintering state.  We propose to assess the energy stores of amphibians at various stages of their yearly cycle in order to ascertain whether variations in the quality of the overwintering environment (in terms of temperature and oxygen) modify post-hibernation energy stores.  Global climate change predicts progressively warmer winters, yet it is not necessarily the case that high temperatures will lead to increased survival for amphibians.  Warmer temperatures may lead to energy 'wasting' as a result of the increased metabolism.  A bomb calorimeter can directly measure the total energy content and give insight into how much fat or glycogen stores animals possess, and thus allow predictions of overwintering survival and reproductive fitness.  A bomb calorimeter is cost effective means of bringing laboratory techniques to a field station since it requires little technical and personnel support yet yields physiologically and ecologically meaningful results.