Multiphasic allometry: the reality and significance of ontogenetic shifts in the body-mass scaling of metabolic rate

Commonly observed multiphasic ontogenetic scaling of the rate of metabolism with body mass deserves increased attention because metabolism fuels all biological processes, including growth and development. Traditionally, developmental biologists have largely overlooked how ontogenetic transitions are powered by metabolic energy. The reality of multiphasic allometry in some species has also been challenged based on statistical grounds. Therefore, this article attempts to provide helpful perspectives about the reality and significance of multiphasic ontogenetic allometry in three ways. First, it is argued that recent statistical criticisms of multiphasic allometry are problematic because they are based on data that were not properly scaled in geometric (log–log) space and/or on results of analyses of covariance that were distorted by unequal sample sizes and/or unequal/nonoverlapping body-size ranges of the different developmental stages analyzed. Second, it is recommended that the existence of nonlinear (multiphasic or curvilinear) allometry should be tested by comparing linear versus curvilinear regression models or body-size scaling slopes (and their 95% confidence intervals) of different developmental stages, each analyzed with separate, statistically independent log–log regression lines. Third, ontogenetic shifts in metabolic scaling are related to other fundamental developmental changes, thus highlighting the significance of multiphasic allometry for understanding organismal development. Ontogenetic metabolic allometry should be given a more central (general) place in the field of developmental biology.