The effects of in vivo light and temperature acclimation on in vitro responses of heart rate to temperature in a cold-climate reptile, Thamnophis sirtalis parietalis

Abstract

A multifaceted hypothesis regarding seasonal metabolic function in cold-climate reptiles is set forth. It is hypothesized that (1) cold-climate reptiles do not possess a capability for time-dependent temperature compensation; (2) seasonal activity patterns are governed by air–ground thermal gradients; and (3) a metabolic depression is induced by constant darkness during the hibernation period.In vitro rates of heartbeat were measured in relation to temperature in 10 garter snakes (Thamnophis sirtalis parietalis) acclimated for 30 days to each of the following experimental regimes: 32 °C, 8L16D; 32 °C, 0L24D; 5 °C, 8L16D; 5 °C, 0L24D. R–T curves exhibited a triphasic pattern in all cases, with a plateau in the 20.0–25.0 °C range. Time-dependent temperature compensation in the rate of heartbeat did not occur. The R–T curve of the 5 °C, 0L24D treatment group possessed a significant depression, relative to the other three treatment groups, in the region below the plateau. These findings provide preliminary support for aspects of the hypothesis, and create a number of additional hypotheses.