Abstract

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 affect phenotypic traits such as CT_max. Indeed, 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 when the acclimation temperature is higher. However, there is a lack of information about whether amphibians respond differently to long- versus short-term acclimation. Understanding thermal acclimation capacity in response to rapid environmental change is important because high acclimation capacity may reduce vulnerability. Here, we evaluated thermal acclimation capacity in the Eastern Red-backed Salamander, Plethodon cinereus, in response to short- and long-term acclimation 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 an increase in CT _max from the control treatment to the short-term (+0.84 °C) and long-term (+2 °C) acclimation treatments, there was little difference in CT _max between short- and long-term acclimation (0.33 °C), and none of the differences we examined were statistically significant.

Discussion . Several factors may explain the low variation in CT _max despite the thermal variation treatments described in our study. CT _max could be more phylogenetically conserved, or the temperature changes in our treatments may not have been sufficient to elicit a physiological response. Thus, although our results provide limited evidence that there may be a degree of acclimation capacity (or phenotypic plasticity) in CT _max in Plethodon cinereus , different acclimation periods did not affect the degree of plasticity.