France

&quot;Time integrated Field Metabolic Rate (FMR) is arguably the most ecologically relevant measure of the energetics of wild animals, but the relative complexity of determining FMR routinely means that we have relatively few large datasets describing variation in energy use in free-living wild animals, particularly for aquatic ectotherms where double labelled water methods cannot be used.
Emerging proxies based on stable isotope systematics associated with respiration allow retrospective estimation of time integrated field metabolic rate, experienced temperature and growth in any free-living marine teleost fish. Here we present FMR data obtained for 780 individuals from 10 species of fishes sampled within a one month period in the Barents Sea. The dataset includes individual Atlantic cod with a body size range over 4 orders of magnitude, dramatically increasing the body size range over which scaling of field metabolic rates have been assessed for any single species. 
The allometric exponent for body size scaling of FMR is 0.9 across all taxa. Within-species scaling exponents range from 0.7 – 1.2. Mass scaling exponents may be non-linearly related to body size, but these field data are confounded by size-dependent temperature preferences. In all but one species, FMR is relatively insensitive to temperature, implying that FMR is not strongly constrained by external temperatures for fish populations operating within environmental conditions to which the population is adapted/acclimated. 



&quot;

Why and how does metabolic rate scale with body size?

Body size and temperature scaling of field metabolic rate in wild marine fishes

active metabolism

fish

isotope

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CAP Virtual Congress 2021

"Time integrated Field Metabolic Rate (FMR) is arguably the most ecologically relevant measure of the energetics of wild animals, but the relative complexity of determining FMR routinely means that we have relatively few large datasets describing variation in energy use in free-living wild animals, particularly for aquatic ectotherms where double labelled water methods cannot be used.
Emerging proxies based on stable isotope systematics associated with respiration allow retrospective estimation of time integrated field metabolic rate, experienced temperature and growth in any free-living marine teleost fish. Here we present FMR data obtained for 780 individuals from 10 species of fishes sampled within a one month period in the Barents Sea. The dataset includes individual Atlantic cod with a body size range over 4 orders of magnitude, dramatically increasing the body size range over which scaling of field metabolic rates have been assessed for any single species. 
The allometric exponent for body size scaling of FMR is 0.9 across all taxa. Within-species scaling exponents range from 0.7 – 1.2. Mass scaling exponents may be non-linearly related to body size, but these field data are confounded by size-dependent temperature preferences. In all but one species, FMR is relatively insensitive to temperature, implying that FMR is not strongly constrained by external temperatures for fish populations operating within environmental conditions to which the population is adapted/acclimated. 



"

technical paper

Metabolic rate is closely related to body size (body mass), but when mass increases, metabolic rate usually increases less. This allometric scaling relationship between metabolic rate and body mass is fundamental to biology and widely applied, but also one of the most debated concepts in integrative and comparative physiology, ecology, and evolutionary biology.

Several theories and hypotheses have been put forward to explain why and how metabolic rate scales with body mass, and why there appears to be variation in how steep this scaling relationship is among different taxa and physiological or ecological conditions (e.g. 'surface area', 'cell size', 'fractal distribution network', ‘dynamic energy budget’, and ‘metabolic-level boundaries’ theories or hypotheses). However, the lack of consensus on these important topics is a major barrier to our understanding of the pace at which organisms of different sizes and species expend energy and need to consume resources such as food and oxygen from the environment. It also limits our ability to predict how metabolic rate and body size (co)evolves, and how climate change affects metabolic demands and body sizes, as metabolic scaling exponents are used to model how these key organismal traits are affected by changing temperature and oxygen levels. The importance of metabolic scaling is clear, yet it remains one of the most controversial concepts in biology.

The overall aim of this satellite meeting is to bring together researchers working with metabolic scaling, to: (1) bring the field up to speed on state-of-the-art knowledge and research on metabolic scaling; (2) help understand how the vastly different views and opinions on metabolic scaling can persist despite more than a century of research (e.g. scaling in proportion to surface area or not, universal ¾-power scaling or not, governed by ecological vs. physical or geometric factors); and (3) identify and help streamline specific areas of research on metabolic scaling that will be particularly important for our further understanding of why and how metabolic rate scales with body size.

The meeting is being organised as part of the Animal Section of the SEB and will therefore have a focus on metabolic scaling of animals, but work on other organisms is welcome where this can provide insight into metabolic scaling in general.

The overall aim of this satellite meeting is to bring together researchers working with metabolic scaling, to: bring the field up to speed on state-of-the-art knowledge and research on metabolic scaling; help understand how the vastly different views and opinions on metabolic scaling can persist despite more than a century of research (e.g. scaling in proportion to surface area or not, universal ¾-power scaling or not, governed by ecological vs. physical or geometric factors); and identify and help streamline specific areas of research on metabolic scaling that will be particularly important for our further understanding of why and how metabolic rate scales with body size.

Living organisms use energy to grow and reproduce, so the processes of energy metabolism and biological production should be tightly bound. Based on this fundamental tenet, we develop new theory that predicts the relationships between three fundamental aspects of life: metabolic rate, growth, and reproduction. We test and validate this theory using empirical data for more than 10,000 species from 12 phyla, and show that the optimisation of these processes yields the observed allometries of metazoan life. We conclude that metabolic rate, growth, and reproduction are inextricably linked and together determine fitness, and, in contrast to longstanding dogma, that no single component drives another.

Metabolic scaling is the product of life history optimization

Adult body size in insects can be influenced by environmental conditions during larval growth. The effect of such intraspecific variation in body mass on flight performance is poorly understood. In Batocera rufomaculata, a large tree boring beetle, often engaging in dispersal flight, adults emerging from larvae that developed in a dying host tree under nutrient-deprived diet conditions, are smaller than individuals who developed in nutrient rich environments. This leads to a large variation in adult body mass (1 to 7 g) with an expected effect on flight Metabolic Rate (MR). Measuring MR poses a formidable challenge in free-flying insects who can’t breathe into masks or be trained to fly in controlled settings. Consequently, flight MR has been predominantly measured on hovering or tethered insects flying in closed systems. In this study we applied the ‘bolus injection of isotopic 13C Na-bicarbonate’ method to explore the relationship between intraspecific body size and power expended during tethered steady forward flight and free flying B. rufomaculata. While the method was previously used solely on vertebrates, we report a 90% accuracy of the method in our beetle when compared to direct respirometry. We found that free FMR and tethered FMR increased in relation to body mass as 99·𝑀0.54 and 36∙M^0.56 respectfully showing that while the free FMR is ~3 times higher than FMR recorded in tethered flight, the mass exponent remains unchanged. This mass exponent of ~0.55 is lower than the expected exponent for interspecific variation in body mass of M^0.74 to M^0.98.

The scaling of free flight energetics of the mango stem borer beetle, Batocera rufomaculata

Metabolic scaling theory: New Insights in Scaling Form, Function & Diversity

Seed plants vary tremendously in size and morphology. However, variation and covariation between plant traits may at least in part be governed by universal biophysical laws and biological constants. Metabolic Scaling Theory (MST) posits that whole-organismal metabolism and growth rate are under stabilizing selection that minimizes the scaling of hydrodynamic resistance and maximizes the scaling of resource uptake. This constrains variation in physiological traits and in the rate of biomass accumulation, so that they can be expressed as mathematical functions of plant size with near constant allometric scaling exponents across species. However, observed variation in allometric exponents questions the evolutionary drivers and the universality of scaling exponents. We have measured growth scaling and fitness traits of 451 Arabidopsis thaliana accessions with sequenced genomes. Variation among accessions around the scaling exponent predicted by MST correlated with climate, seed production and stress resistance. Genomic analyses indicate that growth allometry is affected by many genes associated with local climate and abiotic stress response. The gene with the strongest effect, PUB4, has molecular signatures of balancing selection, suggesting that intraspecific variation in growth scaling is maintained by opposing selection on two major components of fitness, seed production and abiotic stress resistance. Our findings support one of the core MST predictions and suggest that allometry contributes to local adaptation to contrasting environments. Our results help reconcile past debates on the origin of allometric scaling in biology, and begin to link adaptive variation in allometric scaling to specific genes.

Adaptive diversification of metabolic scaling in the plant Arabidopsis thaliana

How much energy an organism consumes can be used to make inferences across scales and could be a valuable tool to predict energy fluxes of populations and communities. While scaling patterns can be seen across species and systems, the mechanisms that drive variation in metabolic scaling and influence functioning at larger scales remain unclear. I will present work that explores how competition alters the metabolism of individual organisms, and how these effects change as species coevolve. I will then discuss how competition modifies energy fluxes at larger scales and the implications for predicting community functioning.

How does competition alter metabolism and what are the consequences for community functioning?

Meta-analysis of metabolic rates in three anadromous fishes reveals variation in scaling with mass, temperature and swim speed

Large-scale comparisons of mammalian basal metabolic rates often transform metabolism (using Q10 effects) to approximate a standard body temperature of 37°C. However, existing mammalian body temperature datasets do not take into account the high degree of within-species and within-individual variability in body temperatures. There is increasing recognition that rather than being fully homeothermic, most endotherms display some degree of flexibility in body temperature. Yet existing body temperature datasets use temperatures from different non-analog states (such as resting versus active or scotophase versus acrophase) or mean body temperature, which has increasingly been shown to have little biological relevance. Using a new dataset of standardised resting body temperatures in mammals, we show that the relationship between basal metabolism and body temperature is not as straightforward as has been presumed. We discuss the implications of correcting, or not, for body temperature in studies on metabolic scaling and discuss the role of thermoregulatory phenotypes in shaping mammalian basal metabolic rates.

The role of body temperature in the scaling of metabolic rate in mammals

Metabolism; Scaling; Mammals; Hibernation

Seasonal Changes in the Metabolic Scaling of Hibernating Thirteen-Lined Ground Squirrels (Ictidomys tridecemlineatus)

Metabolism is a fundamental property of organisms as it underpins all life-sustaining processes. The relationship between metabolic rate (R) and body size (M) has become a central topic in ecology, yet the mechanism(s) that underlie this mass dependence (termed scaling) and its variation, remain enigmatic. Metabolic scaling can be affected by temperature and activity, as warming and muscular work not only accelerate metabolic level (L), but often lead to changes in the scaling exponent (or slope b, in log R vs. log M). This change has been explained through a shift of resource supply from volume- to surface-area related processes. However, whether the same supply constraints apply among and within species is unclear, as the quantitative relationship between b and L remains largely untested within species. Only by understanding these patterns we will be able to address proximate and ultimate mechanisms behind metabolic scaling variation. Through a meta-analysis, we quantitatively compare the intra-specific change in b when L is increased by either temperature or locomotor activity in a wide range of ectothermic vertebrates, including fish, amphibians, and reptiles. We show that b decreases with temperature-increased L in water-breathing (fish) but not in air-breathing species (amphibians and reptiles), whereas b increases with activity-increased L in air-breathing but not in water-breathing species. Our findings in the most comprehensive intra-specific analysis of ectothermic vertebrates to date indicate that b varies differently with temperature and activity in water- and air-breathers, and suggest that oxygen availability in water may constrain metabolic scaling of fish.

Intraspecific variation in metabolic scaling with temperature and activity differs between water- and air-breathing ectothermic vertebrates

Metabolic rate (MR) usually changes (scales) out of proportion to body mass (BM) as MR = aBM^b, where a is a normalisation constant and b the scaling exponent that reflects how steep this change is. This scaling relationship is fundamental to biology, but over a century of research has provided little consensus on the value of b, and why it appears to vary among taxa and taxonomic levels. Here, I show that individual variation in fish growth under naturally restricted food availability can explain variation in within-individual (ontogenetic) b for standard metabolic rate (SMR) of brown trout (Salmo trutta); the fastest growers had the steepest metabolic scaling, and within-individual b varied much more widely than previously assumed from work on different individuals or different species, from –1 to 1. The negative b for some individuals was caused by reductions in metabolic rate, likely to maintain positive growth, which resulted in a mean within-individual b that was significantly lower than the across-individual (‘static’) b, a difference that also existed for another species, cunner (Tautogolabrus adspersus). I also show that across-species (‘evolutionary’) b for SMR of 134 fishes is significantly steeper than the mean ontogenetic b for the trout and cunner. I hypothesise that the steeper evolutionary than ontogenetic scaling for fishes could arise as a by-product of natural selection for fast-growing individuals with steep metabolic scaling early in life, where size-selective mortality is high. I support this by showing that b for SMR tends to increase with natural mortality rates of fish larvae within taxa.

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Body size and temperature scaling of field metabolic rate in wild marine fishes

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