Counting the cost of living: mitochondrial efficiency, environmental conditions, and performance in the wild

ended

An organism’s metabolic rate is a central trait that links its physiology with its ecology and life history. However, while textbook definitions of metabolic rate generally refer to the rate of energy use by the animal, most empirical studies instead record it very indirectly as whole-animal oxygen consumption rate, without any actual measurement of ATP production. This approach contains a conceptual weakness: it is equivalent to estimating a car’s capacity or efficiency by measuring its fuel consumption per minute, with no measurement of what that consumption actually achieves in terms of speed or distance travelled. This can significantly weaken our ability to link metabolic rates to ecological processes, and may explain why conventional measures of metabolic rate often do not predict performance or fitness. This ambitious project will therefore attempt to re-dress the balance by shifting the focus onto the efficiency with which mitochondria produce ATP, with the expectation that this will lead to completely new insights into how metabolic rate influences and constrains the behaviour and ecology of animals. It will use new techniques that we have developed for simultaneous measurement of both ATP and ROS production by the mitochondria; these have revealed two-fold variation among individuals in the efficiency of ATP production (and hence ability to perform aerobic work), totally hidden from usual measurements of metabolic rate. I will use these approaches to examine the impact of metabolic efficiency on performance and the trade-off between efficiency and rates of senescence, using freshwater fish as an experimental system. By applying cutting-edge methods, so far only used in the laboratory, to animals living in their natural habitats, the project will reveal for the first time how environmental conditions select for particular mitochondrial phenotypes and hence metabolic efficiency, so allowing a re-evaluation of the links between ecology and metabolic rate.