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

Abstract

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 acclimation (spring vs. autumn) in the lab affected the thermal sensitivity of standard metabolic rates (SMR) and rates of evaporative water loss (EWL) in the spotted salamander (Ambystoma maculatum). We hypothesised that temperature would have both acute and prolonged effects over traits (i.e., exposure to test temperatures and seasonal acclimation, respectively). After accounting for body mass and sex, we found that acute changes in temperature led to an increase in SMR and EWL. Additionally, SMR differed between seasons, but EWL did not. Salamanders had lower SMR in the spring, suggesting that energy may be allocated toward overwintering emergence and breeding. By contrast, maintaining higher SMR in the autumn may allow salamanders to forage aboveground on rainy nights to replenish energy reserves in preparation for the winter. The seasonal constancy of EWL suggests that salamanders should rely on behavioural rather than physiological modulations to mitigate possible detrimental effects of warming over the maintenance of hydric state. 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 hydric requirements.