Phenotypic plasticity is a key generator of biodiversity, with fundamental ramifications for a variety of ecological and evolutionary processes. We will investigate the relative roles of phenotypic plasticity and genetic adaptation for thermal performance in natural amphibian populations. My previous studies have revealed the importance of countergradient variation (CnGV) in local adaptation of populations originating from different thermal environments. We will use transcriptome profiling in a common garden setting to investigate the genomic basis of CnGV. Our central hypothesis is that non-adaptive plasticity allows rapid adaptation of ectotherm populations to changing climate. We will assess variation in gene expression and life history phenotypes along replicated latitudinal gradients and in two local population networks to characterize the genomic foundations of differential temperature-induced phenotypic plasticity across different spatial and temporal scales. This research will generate novel insight into the roles of phenotypic plasticity and genetics in thermal adaptation in an important ecological and evolutionary model system. It will link variation in gene expression and molecular pathways to variation in life history phenotypes across multiple populations at multiple spatial scales. In the face of climate change, this research will add invaluable information on the mechanisms and potential of thermal adaptation in natural populations.