Thermoregulation as a function of thermal quality in a northern population of painted turtles, Chrysemys picta

Abstract

Body temperature affects nearly all processes of ectotherms. Reptiles do not generate sufficient body heat to regulate their body temperature internally and therefore use behavioural thermoregulation. We determined whether thermoregulatory effort varied among seasons in an environment where large temporal differences in environmental temperatures (Te) exist. We took 31 297 internal body temperature (Tb) measurements from 18 painted turtles ( Chrysemys picta (Schneider, 1783)) throughout their active season. We estimated Te with physical models and water temperatures. We measured the range of preferred body temperatures (Tset) in a thermal gradient. Tset was 21.3–25.0 °C. We used Tb, Te, and Tset to calculate standard thermoregulation indices (Ex and de – db). An Ex of 40.7% and a de – db of 2.4 °C indicated that painted turtles are moderate thermoregulators, despite inhabiting a high-cost environment. Effort to regulate Tb increased as the thermal quality of the habitat decreased. Thermoregulatory effort was higher when Tset could not be achieved. Painted turtles put more effort in thermoregulation in the early season than in the rest of the season. This within-species pattern follows the pattern seen among species. This study is the first to measure Tb internally and to apply standard thermoregulation indices to free-ranging turtles.