Meeting Abstract
Mandatory to meal digestion is the expenditure of energy stemming from the breakdown, absorption and assimilation of that meal. The magnitude of this collective energy expenditure, termed specific dynamic action (SDA), is largely a function of meal size. Predictably, any increase in meal size would generate a corresponding increase in SDA. However, unknown is the nature of this relationship. Hypothetically there are three possible scenarios: (1) increase in SDA is matched to the increase in meal size; (2) SDA increases at greater rate compared to the increase in meal size; and, (3) SDA increases at a lesser rate compared to the increase in meal size. We tested among these competing hypotheses by feeding snakes different size meals (5-25% of body mass) and quantifying for each meal size the maximum postprandial metabolism, duration of significant metabolic response, and SDA. We quantified for each of these variables a response coefficient, defined as the factorial increase of that response with a doubling in demand (i.e. meal size). For four species of pythons (Python molurus, P. sebae, P. reticulatus, Morelia viridis), four species of boas (Boa constrictor, Eunectes murinus, Eryx colubrinus, Epicrates cenchria), and the colubrid Pantherophis guttata the response coefficient for maximum postprandial metabolism averaged 1.41 (1.23-1.70) and for duration averaged 1.47 (1.15-2.13). The response coefficient for SDA averaged 2.35 (1.85-2.90). For these snakes, a doubling in meal size resulted on average in a 41% increase in peak postprandial metabolism and a 47% increase in duration that combined to generate a 135% increase in SDA. These findings support the second scenario that with an increase in relative meal size, snakes spend a disproportionately greater amount of energy in digesting and assimilating larger meals.
