Abstract
Metabolic rate is often measured as a phenotype in evolutionary genetics, among other fields including many facets of physiology, behavior, and ecology, because it impacts organismal fitness, is repeatable and heritable, and is responsive to numerous environmental variables. Aquatic respirometry, a method used to measure metabolic rate, has allowed key questions in these fields to be investigated, namely: 1) why do individuals from the same population exhibit up to three fold differences in metabolic rate, 2) how does metabolic rate change during an individual’s lifetime, and 3) what metabolic rate is advantageous in a specific environment? Current respirometry studies often suffer from small sample sizes and rely on low throughput approaches to measure metabolic rate, making it difficult to answer these and other relevant ecological and evolutionary questions due to lack of power, failure to capture true biological variation, and confounding variables, like time, that are introduced due to limitations in methodology. Here we describe a scalable high-throughput intermittent flow respirometer (HIFR) design and use it to measure the metabolic rates of 19 aquatic animals in one night while reducing equipment costs and time by more than 50%.
Highlights
Metabolic rate is often measured as a phenotype in evolutionary genetics, among other fields including many facets of physiology, behavior, and ecology, because it impacts organismal fitness, is repeatable and heritable, and is responsive to numerous environmental variables (Christoffersen et al, 2007; Nespolo and Franco, 2007; Norin and Malte, 2011; Schulte, 2015; Pettersen et al, 2018)
To calculate repeatability the mean sum of squares among and within individuals was taken from the ANOVA, and 3 measures per individual a repeatability of the tenth percentile value of metabolic rate, used here to represent Routine metabolic rate (RMR), was 0.96
Metabolic rates measured in high-throughput intermittent flow respirometer (HIFR) are comparable with values from previously reported metabolic rate values for F. heteroclitus (±5%) and other teleost fish (±40%) further validating the methods described here (Healy and Schulte, 2012; Blewett et al, 2013; Chabot et al, 2016)
Summary
Metabolic rate is often measured as a phenotype in evolutionary genetics, among other fields including many facets of physiology, behavior, and ecology, because it impacts organismal fitness, is repeatable and heritable, and is responsive to numerous environmental variables (Christoffersen et al, 2007; Nespolo and Franco, 2007; Norin and Malte, 2011; Schulte, 2015; Pettersen et al, 2018). Flow through respirometry is achieved by measuring the amount of oxygen entering and leaving a chamber relative to the flow rate of air or water through the chamber (Svendsen et al, 2016b). Closed respirometry places an organism in a sealed chamber of known volume and measures oxygen or carbon dioxide partial pressures at multiple time points throughout the trial. The sealed chamber during closed respirometry may result in the accumulation of nitrogenous waste and carbon dioxide, which can increase stress, and may cause loss of equilibrium (LOE) in aquatic organisms (Snyder et al, 2016). Where MO2 was the minimum metabolic rate of each fish as previously described and background respiration was a chamber specific value calculated by averaging the oxygen consumption over time in each empty chamber across three replicate blank runs.
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