Effects of meal size, meal type, body temperature, and body size on the specific dynamic action of the marine toad, Bufo marinus

Specific dynamic action (SDA), the accumulated energy expended on all physiological processes associated with meal digestion, is strongly influenced by features of both the meal and the organism. We assessed the effects of meal size, meal type, body temperature, and body size on the postprandial metabolic response and calculated SDA of the marine toad, Bufo marinus. Peak postprandial rates of O-2 consumption ((V)over dot(2)) and CO2 production ((V)over dotCO(2)) and SDA increased with meal size (5%-20% of body mass). Postprandial metabolism was impacted by meal type; the digestion of hard-bodied superworms (Zophobas larva) and crickets was more costly than the digestion of soft-bodied earthworms and juvenile rats. An increase in body temperature (from 20degrees to 35degreesC) altered the postprandial metabolic profile, decreasing its duration and increasing its magnitude, but did not effect SDA, with the cost of meal digestion remaining constant across body temperatures. Allometric mass exponents were 0.69 for standard metabolic rate, 0.85 for peak postprandial (V)over dot(2), and 1.02 for SDA; therefore, the factorial scope of peak postprandial (V)over dot(2) increased with body mass. The mass of nutritive organs (stomach, liver, intestines, and kidneys) accounted for 38% and 20% of the variation in peak postprandial (V)over dot(2) and SDA, respectively. Toads forced to exercise experienced 25-fold increases in (V)over dot(2), much greater than the 5.5-fold increase experience during digestion. Controlling for meal size, meal type, and body temperature, the specific dynamic responses of B. marinus are similar to those of the congeneric Bufo alvarius, Bufo boreas, Bufo terrestris, and Bufo woodhouseii.