Determinants and repeatability of the specific dynamic response of the corn snake, Pantherophis guttatus

Ingesting, digesting, absorbing, and assimilating a meal are all energy consuming processes that accumulate to form the specific dynamic action (SDA) of the meal. Sensitive to digestive demand, SDA is theoretically fixed to a given meal size and type. In this study, we altered relative meal size to explore the effects of digestive demand on the postprandial metabolic profile and SDA of the corn snake, Pantherophis guttatus. We also examined the effects of body temperature on the SDA response while controlling for meal size and type and assessed whether these responses are highly repeatable under the same conditions. Additionally, the effects of body mass on SDA were investigated by feeding snakes the same relative and absolute meal size. With increases in digestive demand (meals from 5% to 45% of body mass), P. guttatus   responded with incremental increases in the postprandial peak in oxygen consumption (V˙ O2), the duration of the significantly elevated V˙ O2, and SDA. Body temperature had an observable impact on the postprandial metabolic profile, decreasing the duration and increasing the peak V˙ O2, however, body temperature did not significantly alter SDA. Regardless of temperature, and hence duration, snakes expended the same amount of energy in digesting a given meal. This was additionally borne out when testing the individual repeatability of the SDA response, individual P. guttatus exhibited nearly identical postprandial responses to the same meal. Over a 90-fold range in body mass, and fed meals equaling 25% of body mass, P. guttatus exhibited an isometric relationship between SDA and body mass. When fed a set 10-gram meal, snakes regardless of body size expended the same amount of energy on digestion and assimilation. Characteristically, P. guttatus experience a rapid postprandial increase in metabolic rate that peaks and gradually descends to prefeeding levels. The magnitude of that response (quantified as SDA) varies as a function of digestive demand (i.e., meal size); however, when demand is fixed, SDA is constant regardless of body temperature and body size.