FAULKNER, A.C.; SECOR, S.M.: Determinants of post-feeding response of the toad Bufo marinus

Feeding stimulates an increase in metabolic rate and the summation of the energy expended on the ingestion, digestion, absorption, and assimilation of a meal is termed specific dynamic action (SDA). Previously, studies documented the effects of one or two of the following variables on SDA; meal size, meal composition, body temperature, and body size. In this study, we evaluated the influence of each of these four variables on the SDA of the toad Bufo marinus. Toads (at 30 C) responded to an increase in meal size (rodent meals ranging from 5 to 20% of toad body mass) with matched increases in metabolic rate (3- to 7-fold of standard metabolic rate (SMR)) and overall SDA (50 – 380 kJ/kg). At a given meal size (rodent meals equaling 10% of body mass), differences in body temperature (20 – 35 C) had little influence on the relative increase in metabolic rate and SDA. However, body temperature did significantly effect the duration of the metabolic response, lasting 8 days at 20 C and shortened to 2.5 days at 35 C. Metabolic response and SDA differed significantly among different meal types. Weighing 10% of body mass, rodent and earthworm meals generated a lower SDA than cricket and superworm (Zophobas) meals. The most energy efficient meals were rodents (SDA = 15% of ingested energy), whereas the least efficient were earthworms (SDA = 35% of ingested energy). Over a 150-fold range in body mass (2 – 300 g), SDA (stemming from a 10% rodent meal at 30 C) scaled lineraly (mass exponent = 1.02) with body mass, whereas SMR and the combined masses of the stomach, small intestine and large intestine scaled, respectively, with mass exponents of 0.67 and 0.81.