Relationship of metabolic rate to body size in Orthoptera

Authors: Fielding, Dennis; Defoliart, Linda

Submitted to: Journal of Orthoptera Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2008
Publication Date: 12/20/2008
Citation: Fielding, D.J., Defoliart, L.S. 2008. Relationship of metabolic rate to body size in Orthoptera. Journal of Orthoptera Research. 17(2):301-306.

Interpretive Summary: Typically, larger organisms have a lower metabolic rate, per unit of mass, than smaller organisms. Because metabolic rate influences many life processes such as an individual’s rate of resource acquisition, assimilation, growth, survival, and reproduction, the relationship of metabolic rate to body size has been a subject of intense scrutiny. Studies involving a broad range of taxa and body sizes typically result in whole-organism metabolic rate scaling to the ¾ power of body mass, that is, for a 4-fold increase in body weight, metabolic rate increases only 3-fold. Competing models have been proposed to explain this allometric relationship. The nutrient supply network model of West et al. (1997) proposes that the ¾ power relationship results from the fractal nature of space-filling nutrient supply networks. The model of Kozlowski et al. (2003) proposes that the scaling of metabolic rate with body mass will vary from 2/3 to 1 among different taxa, depending on the degree to which increasing body size depends on increasing cell size or number. The present study measured resting metabolic rates across a broad range of body sizes in nymphs and adults of Melanoplus sanguinipes F. and also analyzed published reports of metabolic rates in adult Orthoptera. The two sets of data were in close agreement: the scaling exponent for the ontogenetic series of M. sanguinipes was 0.923, and for the interspecific compilation of adult Orthoptera, it was 0.918. Both scaling exponents were significantly greater than the 0.75 predicted by the nutrient supply network model. This information will help to understand how metabolic processes of individuals affect life histories and population dynamics of Orthoptera, including many pest species of grasshoppers.

Technical Abstract: Metabolic rate determines an individual’s rate of resource acquisition, assimilation, growth, survival, and reproduction. Studies involving a broad range of taxa and body sizes typically result in whole-organism metabolic rate scaling to the ¾ power of body mass. Competing models have been proposed to explain this allometric relationship. The nutrient supply network model of West et al. (1997) proposes that the ¾ power relationship results from the fractal nature of space-filling nutrient supply networks. The model of Kozlowski et al. (2003) proposes that the scaling of metabolic rate with body mass will vary from 2/3 to 1 among different taxa, depending on the degree to which increasing body size depends on increasing cell size or number. The present study measured resting metabolic rates across a broad range of body sizes in nymphs and adults of Melanoplus sanguinipes F. and also analyzed published reports of metabolic rates in adult Orthoptera. The two sets of data were in close agreement: the scaling exponent for the ontogenetic series of M. sanguinipes was 0.923, and for the interspecific compilation of adult Orthoptera, it was 0.918. Both scaling exponents were significantly greater than the 0.75 predicted by the nutrient supply network model.