Conclusions
Studies focusing on seedling adaptive potential to multivariate stressors mimicking changing climatic conditions are timely given the focus on assisted migration efforts. A multitude of common garden experiments and genome-wide association studies provide remarkable evidence for local adaptation and GEI (Langlet, 1971; Savolainenet al ., 2013). Here, we demonstrate strong evidence of adaptive evolution and GEI at both the per-transcript and co-expression module levels, with partial evidence that these patterns interact with interspecific gene flow through the survival component of fitness. We further highlight that populations of long-lived tree species may be more able than expected to respond to rapidly changing climatic conditions through ample genetic variation underlying expression traits and a modulation of genetic architecture depending on the degree and direction of environmental change. This response, moreover, appears to be provided by pleiotropic loci underlying strongly connected adaptive expression traits. The generality of our primary finding of rapid adaptive potential aided by pleiotropic loci additionally awaits further work across phylogenetically diverse tree species distributed across various climatic gradients with differing demographic histories.