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

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.

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.

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.

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.