Solving the conundrum of intra‐specific variation in metabolic rate: A multidisciplinary conceptual and methodological toolkit

Abstract

Researchers from diverse disciplines, including organismal and cellular physiology, sports science, human nutrition, evolution and ecology, have sought to understand the causes and consequences of the surprising variation in metabolic rate found among and within individual animals of the same species. Research in this area has been hampered by differences in approach, terminology and methodology, and the context in which measurements are made. Recent advances provide important opportunities to identify and address the key questions in the field. By bringing together researchers from different areas of biology and biomedicine, we describe and evaluate these developments and the insights they could yield, highlighting the need for more standardisation across disciplines. We conclude with a list of important questions that can now be addressed by developing a common conceptual and methodological toolkit for studies on metabolic variation in animals.

Consequences of the cost of living: is variation in metabolic rate evolutionarily significant?

“…Ongoing technological advances are increasing both the throughput and precision of metabolic rate measurements, and providing previously unexplored insights into metabolic rate variation [4]. Thoral et al [33] provide a new method for repeated non-destructive sampling of mitochondrial function in individuals through time.…”

Tissue-specific metabolic enzyme levels covary with whole-animal metabolic rates and life-history loci via epistatic effects

“…Species and populations can show substantial and adaptive variation in wholeanimal metabolic rate [1][2][3], which can be an important target for selection, as metabolism affects the allocation of energy to fitness-related traits, potentially constraining life-history evolution [4]. Understanding the evolutionary origins of variation in metabolic rates, such as standard/basal (SMR/BMR) and maximum/active (MMR) metabolic rates is, however, challenging, due to the complexity of underlying mechanisms and plasticity in them [3,[5][6][7]. For example, cellular metabolism exhibits temporal and spatial compartmentalization in different cell types and tissues during development, in different environmental conditions, and across life stages [8], leading to differences in energy allocation and functions among tissues, and subsequently, ecology of the species.…”

Interactive effects of intrinsic and extrinsic factors on metabolic rate

“…Given that metabolism can only occur as a result of a dynamic interaction between the internal and external environments of an organism, it is not surprising that many kinds of intrinsic (biological) and extrinsic (external environmental) factors can affect its tempo [1][2][3][4][5][6][7][8][9][10]. Understanding what causes the broad variation in metabolic rate that exists in the living world is a fundamental challenge in biology because metabolic rate is an important indicator of the 'pace of life', which can significantly influence the ecological success and evolutionary fitness of organisms ( [5,[10][11][12]; but see [13,14]). After many decades of research, we now know much about the effects of many intrinsic and extrinsic factors, especially body size, activity level and temperature, on metabolic rate both within and among species [8,[15][16][17][18][19][20][21][22][23][24].…”