Effects of temperature, photoperiod and season on in vitro metabolic rates of tissues from Thamnophis sirtalis parietalis, a cold climate reptile

Abstract

1. 1. Oxygen consumption of liver, heart and skeletal muscle homogenates was measured in vitro from 4 to 34°C for Thamnophis sirtalis parietalis acclimated to 26°C, 12L 12D; 4°C, 12L 12D; and 4°C, 0L 24D in summer and winter. 2. 2. In most cases, the relationship of metabolic rate (μmoles O 2/mg protein per hr) to immediate temperature change was biphasic, with a low Q 10 at high temperatures and a high Q 10 at low temperatures. 3. 3. Acclimation to 4°C, 12L 12D resulted in a decrease in the metabolic rate of liver and an increase in the metabolic rate of heart at low temperatures, relative to the 26°C, 12L 12D group. The metabolic rate of skeletal muscle was increased by cold acclimation during the summer, but was unaffected during the winter. 4. 4. Acclimation to 4°C, 0L 24D in winter (simulated hibernating conditions) resulted in an increase in the metabolic rate of liver and a decrease in the metabolic rate of heart at low temperatures, relative to the 4°C, 12L 12D group. The metabolic rate of skeletal muscle was not affected at temperatures below 12°C. 5. 5. Seasonal differences were observed in metabolic rates of tissues from individuals held under constant conditions. The nature and magnitude of these differences depended on the acclimation state of the intact organism and the tissue in question. 6. 6. Cold acclimation caused a decrease in the metabolic rates of liver and skeletal muscle from T. sirtalis concinnus, a warm temperate sub-species. 7. 7. In T. sirtalis parietalis, adjustment of metabolic rates to changing energy conditions (temperature and food) in the environment is regulated by a complex interaction of direct thermal effects, photoperiodic effects and inherent seasonal rhythms.