Effect of temperature acclimation period on upper thermal tolerance in a terrestrial salamander

Background Physiological traits, such as the critical thermal maximum (CT max , defined as an individual’s upper thermal tolerance limit), can be important for understanding species’ vulnerability to climate and habitat change. A separate trait, thermal acclimation capacity, is defined as the physiological adjustment of organisms to temperature variation, which can influence phenotypic traits such as CT max . The relationship between acclimation capacity and CT max has been widely studied in ectotherms like fish, amphibians, and reptiles, and it is generally observed that CT max increases with higher acclimation temperatures. However, there is a lack of information about whether amphibians respond differently to long- versus short-term acclimation. Understanding thermal acclimation capacity under rapid environmental change is important, as high acclimation capacity may reduce vulnerability. Here, we evaluated the thermal acclimation capacity of the Eastern Red-backed Salamander, Plethodon cinereus , in response to short- and long-term acclimation treatments in a laboratory setting. Methods We exposed salamanders to three different treatments: control animals were maintained at 15 °C for 30 days; animals in the short-term acclimation group were maintained at 15 °C for 28 days, and 23 °C for 48 hours before testing CT max ; and animals in the long-term acclimation group were maintained at 23 °C for 30 days. We measured the CT max of all animals at the end of the experiment to determine whether tolerance to high temperatures varied depending on the length of exposure to warm conditions. Results Although we observed a slight increase in CT max from the control treatment to the short-term (+0.93 °C) and long-term (+0.98 °C) acclimation treatments, the difference in CT max between acclimation treatments was small (0.05 °C), and none of the differences were statistically significant. Discussion Several factors may explain the low variation in CT max described in our study, including phylogenetic conservation of upper thermal limits, or a lack of sufficient temperature differences in our treatments to elicit a physiological response. Regardless, our results provide limited evidence that different acclimation periods affect the degree of phenotypic plasticity in CT max in Plethodon cinereus .