School of Life and Environmental Sciences, Hangzhou Normal University,,,,College of Life and Environmental Sciences,Wenzhou University
The thermal acclimatory capacity of a particular species determines its tolerance to environmental changes and affects its survival under future changing climatic conditions. Acclimation effects on physiological traits have been determined in many fish and frog species, but rarely in newts or salamanders. In the present study, we evaluated the physiological acclimatory response of newts. A total of 48 juvenile Chinese fire-belly newts (Cynops orientalis) were collected and acclimated to 15℃, 20℃, and 25℃, which represented the low, intermediate, and high environmental temperatures experienced by C. orientalis during their active period, respectively, over the course of 4 weeks. The locomotor (swimming) performances of individuals were measured at the same three test temperatures in a glass tank (150 cm×10 cm×15 cm) filled with water to a depth of 5 cm, and the critical thermal minimum (CTMin) and maximum (CTMax) were determined using a dynamic method. The thermal resistance range (TRR) was calculated as the difference between CTMax and CTMin, and acclimation response ratio (ARR) of CTMin and CTMax was obtained by dividing the tolerance change by the change in acclimation temperature. The results from repeated-measures ANOVA analyses revealed that newt swimming speeds were significantly affected by the acclimation and test temperatures. Despite no statistically significant difference, low and intermediate temperature-acclimated newts had relatively high mean swimming speeds at 15℃ and 20℃, respectively, while the high-temperature-acclimated newts had superior swimming speeds at 25℃. Similarly, at 15℃, low temperature-acclimated newts swam faster than those acclimated to a high temperature. However, at 20℃, intermediate temperature-acclimated newts swam faster than low or high temperature-acclimated individuals, while at 25℃, high and intermediate temperature-acclimated newts swam faster than those acclimated to low temperature. Thus, our data supports the beneficial acclimation hypothesis, which predicts that acclimation to a particular temperature enhances the animal's performance or fitness at that temperature. Our results also indicate that temperature acclimation shifts the thermal sensitivity of swimming performance in C. orientalis since low temperature-acclimated newts appear to have lower thermal sensitivity levels than those acclimated to high temperature. Both CTMin and CTMax were significantly enhanced at higher acclimation temperatures, suggesting that juvenile newts acclimated to low temperatures are more resistant to low temperatures and less resistant to high temperatures, whereas those acclimated to high temperatures are more resistant to high but less resistant to low temperatures. These results are consistent with previous studies focused on the various ectothermic vertebrate species analyzed to date. The TRR of newts was not affected by acclimation temperature, while the ARR of CTMax (0.26) was higher than that of CTMin (0.09) at acclimation temperatures between 15℃ and 20℃, but lower at acclimation temperatures between 20℃ and 25℃ (CTMax:0.16 vs CTMin:0.21). These results are consistent with previous predictions that the magnitude of the change in CTMin or CTMax slowly decreases and ultimately approaches zero as the acclimation temperature gradually reaches its thermal limits. Inter-species differences in thermal physiological response to acclimation in amphibians may be correlated with differences in thermal environments in their natural habitats.