Periodic Reporting for period 3 - MitoWild (Counting the cost of living: mitochondrial efficiency, environmental conditions, and performance in the wild)
Reporting period: 2022-10-01 to 2024-03-31
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 the rate of production of the energy molecule ATP. 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 project is therefore attempting 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 is examining the impact of metabolic efficiency on performance and the trade-off between efficiency and rates of senescence, using freshwater fish as an experimental system, and measuring performance in a range of ecological contexts (e.g. competing for resources in natural conditions, performing parental care etc). This will allow a re-evaluation of the links between ecology and metabolic rate.
The start-up phase of the project involved recruiting and training the team, setting up the aquarium rooms, testing protocols for whole-animal measurements of animal performance (e.g. locomotor performance), developing methods for quantifying use of refuges (using PIT tag detectors embedded in refuges) and use of energy (by means of changes in body shape assessed from analysis of photographs), developing methods for mitochondrial respirometry, collecting fish, testing the assays and conducting the first experiments. The covid outbreak caused a significant interruption to the programme of work, but the first experiments have now been successfully completed, and the data have been processed and been subjected to preliminary statistical analysis. The first papers from the project are now being written.
The project is using new techniques for measurement of both ATP production and the production of reactive oxygen species (ROS) by the mitochondria. These approaches are being used 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 on laboratory animals, to animals of wild origin living in semi-natural or 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.