An energy budget comparison of two populations of garter snakes (Thamnophis sirtalis) found in different environments

Common garter snakes (Thamnophis sirtalis) are the most abundant and widely distributed snakes in North America. They are found in various habitats and have a diverse prey selection. My main objective was to determine if energy allocation among the competing segments of the energy budget differs in two populations, Grand River Wildlife Area, OH (GRWA) and Spruce Knob Lake, WV (SKL), occupying different thermal environments. Using standard common-garden experimental techniques, I compared energy allocated to maintenance, digestion, reproduction and growth. I characterized the two thermal environments using historical weather data and physical snake models placed at each location. Energy allocated to maintenance, digestion, and reproduction were determined by measuring metabolic rates. Bomb calorimetry was used to measure caloric content of neonates. Energy allocated to growth was determined by measuring weight and linear growth over a five week period while snakes were fed weekly and kept at a constant body temperature.; The historical weather data and data collected with the snake models suggest the thermal environment at SKL is more challenging than at GRWA. Snakes at GRWA have more hours available to thermoregulate at 28°C or greater than snakes at SKL do. I did not find any significant differences between the two study sites in most of the comparisons. However, as expected, resting metabolic rates increased with increasing body temperature and specific dynamic action (SDA) increased significantly with meal size but was not influenced by body temperature. Food consumption declined while postabsorptive metabolic rates increased during pregnancy. SKL females had significantly longer gestation periods and allocated less energy to neonates compared to GRWA females.; The two populations of garter snakes examined in this study responded similarly under common conditions. SKL snakes may grow more slowly and either reach reproductive maturity later or at a smaller size because of the cooler temperatures. The increased metabolic rates (∼3 times above resting) during gestation may contribute to the observed anorexia during pregnancy. In addition to egg production, the increased metabolic rates to support pregnancy and the potential energy lost as a result of anorexia contribute significantly to the overall cost of reproduction. In summary, this study reports the most thorough examination of metabolic rates during pregnancy in viviparous snakes, and possibly viviparous squamates.