SECOR, S.M.; Univ. of Alabama, Tuscaloosa: Allometry of SDA, scaling the metabolic response to digestion

The attention on the allometric effects of body mass on metabolism has predominately been focused on basal (or standard) and maximum metabolic rates. The growing interest in the metabolic states associated with meal digestion warrants an investigation of their allometric relationships. Here I present intra- and interspecific allometric relationships of postprandial metabolism and overall specific dynamic action (SDA) for several groups of reptiles and amphibians. For three snake species (Python molurus, Crotalus cerastes, and Pituophis melanoleucus) and the anuran Bufo marinus peak postprandial rates of oxygen consumption and SDA (kJ) scale, respectively, with intraspecific mass exponents ranging from 0.85 to 0.90 and from 1.00 to 1.02. For each species, these scaling exponents are significantly greater than the scaling of their standard metabolic rate (0.68 – 0.73). For ten species of anurans (2.4 – 115 g) digesting cricket meals equaling 10% of body mass, SDA (kJ) scales interspecifically with a mass exponent of 1.28, whereas for four species of colubrid snakes digesting rodent meals equaling 25% of body mass, SDA scales with a mass exponent of 1.07. Potentially contributing to these scaling relationships is the mass and function of digestive organs. Combined mass of digestive organs for the four previously noted species scale with mass exponents ranging from 0.91 to 1.02. Small intestinal nutrient uptake capacity of P. molurus scales with a mean mass exponent of 1.02, while intestinal uptake capacity for proline scales interspecifically among seven anuran species with an exponent of 0.98.