Specific Dynamic Action of a Large Carnivorous Lizard, Varanus albigularis

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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 (V̇O 2) 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 V̇O 2 to peak within 24–27 hr at 7–10 times pre-feeding values (mean = 0.035 mL O 2 · g −1 · h −1). During the 60–90 hr of significantly elevated V̇O 2, 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.