STARCK, J.M.; WERNER, R.; MOSER, P.; University of Munich (LMU), Germany; MPI Biogeochemistry, Jena, Germany; University of Munich (LMU), Germany: Source of Fuel for Post-Feeding Metabolic Responses in Python regius

The postprandial response of pythons has been characterized frequently. Pattern of organ size change, up-regulation of metabolic rate (SDA) and shifts in biochemical blood parameters are well known. The sources of energy supply for the up-regulation of metabolic rate and the up-regulation of organ size remained unknown. We investigated the energy source fueling the post-feeding metabolic up-regulation (specific dynamic action, SDA) in pythons (Python regius). Our goal was to distinguish between two competing hypotheses; 1) snakes fuel SDA by metabolizing their adipose tissue, or alternatively, 2) snakes fuel SDA by metabolizing their prey. To characterize the postprandial response of pythons we used transcutaneous ultrasonography for the measurement of organ size changes, and respirometry to record oxygen consumption. To discriminate unequivocally between the two hypotheses, we enriched prey with the stable isotope of carbon (13C). For 2 weeks after feeding we quantified the CO2 exhaled by pythons and determined its isotopic 13C/12C ratio. Ultrasonography and respirometry showed typical postprandial responses in pythons. After feeding, the isotope ratio of the exhaled breath changed rapidly to values that characterized enriched mouse tissue, followed by a very slow change towards less enriched values during a period of two weeks after feeding. We conclude that pythons metabolize their prey to fuel SDA. The slowly declining delta 13C-values indicate that less enriched tissues (bone, cartilage, collagen) from mouse become available after several days of digestion. The results from our experiment provide evidence against previous hypotheses (pay-before-pumping) that assumed that SDA is fueled from adipose tissue stores of snakes.