Seasonal plasticity in the thermal sensitivity of metabolism but not water loss in a fossorial ectotherm

Ectotherms from highly seasonal habitats should have enhanced potential for physiological plasticity to cope with climatic variability. However, whether this pattern is applicable to fossorial ectotherms, who are potentially buffered from thermal variability, is still unclear. Here, we evaluated how seasonal acclimatisation (spring vs. autumn) affected the thermal sensitivity of standard metabolic rates (SMR), rates of evaporative water loss (EWL), and skin resistance to water loss ( R _s ) in the spotted salamander ( Ambystoma maculatum ). We hypothesised that temperature would have both short- and long-term effects over traits (i.e., acute exposure to test temperatures and seasonal acclimatisation, respectively). After accounting for body mass and sex, we found that short-term changes in temperature led to an increase in SMR, EWL, and R _s . Additionally, SMR and R _s differed between seasons, but EWL did not. Sustaining low SMR and high R _s in the spring may allow salamanders to allocate energy toward overwintering emergence and breeding while simultaneously maximising water conservation. By contrast, maintaining high SMR and low R _s in the autumn may allow salamanders to forage aboveground on rainy nights to replenish energy reserves in preparation for the winter. Despite the common assumption that fossorial ectotherms are buffered from thermal effects, our study shows that functional differences between seasons (i.e., breeding in the spring and provisioning in the autumn) are accompanied by seasonal changes in energetic and hydroregulatory requirements.