Metabolic Scaling: A New Perspective Based on Scaling of Glycolytic Enzyme Activities

Abstract

The decline of mass specific aerobic metabolic rates with increasing animal size has a long history of study in zoology. Attempts to explain this phenomenon have generally been concerned only with aerobic metabolism and with estimators of muscle and skeletal strength. Our finding of tremendous increases in mass-specific glycolytic enzyme activity in locomotory muscle with size in some species of pelagic fishes indicates that this approach has been too narrow. It is necessary to consider total metabolic power in any consideration of metabolic scaling in relation to skeletal strength or muscle power, since the anaerobic component of muscle power is usually greater than the aerobic and often scales differently. We show that scaling of glycolytic power appears to be much more variable among species than is scaling of aerobic power, and we suggest that the different glycolytic power scaling patterns reflect selection for different sprint swimming abilities in fishes of different habits. The rather narrow range of variation in aerobic scaling patterns suggests that they are the result of natural selection acting in the context of geometric constraints on maximum aerobic gas uptake and transport. The glycolytic scaling data emphasize that the role of natural selection has usually been neglected in considerations of scaling of metabolism while the role of the scaling of solids has been overemphasized.