Specific dynamic action of a large carnivorous lizard, Varanus albigularis.

Varanus albigularis inhabits grasslands of southern and eastern Africa and experiences months of fasting during the dry season (May-December) followed by voracious feeding during the wet season (January-April). Previous studies have found that sit-and-wait foraging snakes, which also experience long intervals between large meals, exhibit unprecedented increases in post-feeding metabolism, which reflects the added cost of up-regulating a previously quiescent gut and digesting a large meal. Hence we measured pre- and post-prandial oxygen consumption rates (VO2) of adult V. albigularis in order to observe whether they exhibit similarly large metabolic responses to digestion as sit-and-wait foraging snakes. Following the consumption of meals consisting of ground turkey and snails, hard-boiled eggs, or juvenile rats, lizards rapidly increased their VO2 to peak within 24-27 hr at 7-10 times pre-feeding values (mean = 0.035 mL O2.g-1.h-1). During the 60-90 hr of significantly elevated VO2, the extra oxygen consumed (the specific dynamic action) represented an energy expenditure of 830-1260 kJ. For meals that were fully digested, specific dynamic action equalled 24% of ingested energy. The magnitudes of V. albigularis post-prandial metabolic responses are similar to those previously observed for sit-and-wait foraging snakes. Like sit-and-wait foraging snakes, V. albigularis may also down-regulate intestinal performance during their months of fasting (suggested by their relatively low standard metabolic rate) and then up-regulate their gut (bearing its high energetic cost) upon feeding.