Individual variation in seasonal acclimation by sympatric amphibians: A climate change perspective

Many ectotherms modify their phenotype seasonally as a response to variation in abiotic factors. Given the potential of seasonal acclimation to reduce the impact of climate change on the dynamics of ectotherm populations, the adaptive evolution of this reversible plasticity has received much attention. Nevertheless, the key assumption of selection on the magnitude of seasonal acclimation, consistent among-individual variation (repeatability), remains unexplored. We studied the short- (across body temperatures) and long-term (over two consecutive years) repeatability of seasonal acclimation on standard metabolic rate (SMR) and spontaneous locomotor activity (SLA) in two sympatric newt taxa, Ichthyosaura alpestris and Lissotriton vulgaris. We exposed the newts to various fluctuating thermal regimes over spring and summer and measured SMR and SLA at three body temperatures in each individual over two consecutive years. We quantified seasonal acclimation as difference between summer and spring trait values. We show that individuals of both species vary substantially in their seasonal acclimation responses. Body temperature affected the population means of seasonal acclimation in a quadratic I. alpestris or linear L. vulgaris fashion. Both short- and long-term repeatability of SMR and SLA seasonal acclimation were poor and both species varied in the amount of total variation in the plastic response. Seasonal shifts in environmental temperatures showed high variation between years, but with no apparent trend attributable to local climate change. Our results demonstrate that seasonal SMR and SLA acclimation prevents the establishment of a consistent relationship between individual trait values and environmental gradients, which may limit the adaptive evolution of this plastic response. Disparate thermal dependence patterns and the amount of total variation in seasonal acclimation suggest a species-specific ability for coping with stochasticity of seasonal variation in the thermal environment. To sum up, information on individual variation and population means measured across ecologically realistic body temperatures is necessary to fully understand the occurrence of seasonal acclimation across taxa and its role in the adaptive capacity to climate change. A free Plain Language Summary can be found within the Supporting Information of this article.