The breakdown of food and absorption of nutrients are essential physiological processes in animals. Differences in response to feeding have been attributed to a variety of ecological factors such as foraging mode and body shape, but other ecological attributes could lead to differences in important behaviors and physiological ecological interactions as well. Comparing species energy use gives insight into how species allocate energy for survival and what changes in their habitat could affect that energy use. Measuring the amount of energy an organism uses in response to feeding can be accomplished by measuring its oxygen consumption and using it to calculate pre-feeding energy use (Standard Metabolic Rate; SMR) and post-feeding energy use (Specific Dynamic Action; SDA). We compare responses to feeding between two similar species with differing use of habitat; copperheads (Agkistrodon contortrix; a terrestrial species) and cottonmouths (Agkistrodon piscivorus; a semi-aquatic species). To make these comparisons we measured pre- and post-feeding metabolic rates (at 20, 25, and 30°C) and body temperature selection by digesting snakes. We used an open-system respirometer to measure metabolism and a laboratory thermal gradient to measure body temperature selection. We selected these two species because of their similar evolutionary histories and ecologies and predicted that they would have dissimilar physiological and behavioral responses to feeding because of their differing use of habitat.
Results/Conclusions
We collected 101 SMR’s, calculated 27 SDA’s, and compared 14 snakes pre- versus post-feeding body temperatures between A. piscivorus and A. contortrix. SMR was not significantly different between the species and following the consumption of rodent meals, SDA followed a similar trend of non-significance at the test temperatures. These results suggest that both species of Agkistrodon allocate energy similarly towards digestion. If these two species do not have differing energetic responses when digesting, even at different temperatures, then we would predict in a thermal gradient with no external pressures acting on behavior, both species would behave similarly. Post-feeding, A. contortrix did not select different temperatures but A. piscivorus selected 5-6°C warmer temperatures. After feeding, A. contortrix selected a mean post-feeding temperature of 26°C and A. piscivorus selected a mean post-feeding temperature of 29°C. These behavioral results do not support the prediction set by our metabolic results, indicating that another variable is having an effect on snakes post-feeding behavior. These results indicate that habitat use has an effect on behavior, even when that behavior does not have an apparent physiological energetic benefit.