1School of Sport, Exercise and Health Sciences, Loughborough University, 2Department of Anthropology, Yale University, 3Yale School of Medicine, Yale University, 4Department of Archaeology, University of Cambridge, 5Department of Life Sciences, Anglia Ruskin Ruskin, 6Department of Anthropology, University of Western Ontario, 7Department of Archaeology, Max Planck Institute for the Science of Human History, 8Childhood Nutrition Research Centre, UCL Institute of Child Health
April 16, 2020 , Platinum Ballroom
Life history theory predicts the existence of trade-offs between competing physiological functions. In the absence of increased energy availability, a greater allocation of energy toward one trait necessitates reduced investment in others. The core metabolic cost of self-maintenance (measured by resting metabolic rate, RMR), varies significantly between individuals. However, the fitness consequences are unclear.
This study tests whether there is a trade-off between a measure of maintenance (RMR) and fitness (fluctuating asymmetry, FA). FA reflects growth quality and is linked to success in both intra and intersexual selection. Two theories predict contrasting relationships between RMR and FA. The ‘Increased intake’ hypothesis contends that RMR reflects metabolic capacity, with high RMRs allowing greater energy allocation to growth, reducing FA. Conversely, the ‘Compensation’ hypothesis predicts that high RMRs consume energy, reducing energy for growth, increasing FA.
Measurement of RMR and FA in university rowers revealed a significant positive correlation amongst men (n=57, r=0.344, p=0.009, 1-tailed), and a weak non-significant positive relationship amongst women (n=48, r=0.142, p=0.169, 1-tailed). The results provide support for the ‘Compensation’ hypothesis in males, but not females. Intersexual selection favours low FA in both sexes, while intrasexual selection favours larger body size in males only. Male selection for both growth quality and quantity may therefore impose a greater energy stress, resulting in the positive relationship observed here.
Food availability is thought to modulate the fitness consequences of RMR variability. As rowing imposes high energy demands, further work is required to investigate the effect of energy balance on this trade-off.
This study was funded by the European Research Council under the European Union’s Seventh Framework Programme, Grant/Award Number: (FP/2007-2013)/ERC Grant Agreement n.617627 to Jay Stock.