How the genomics of adaptation to climate and post-Pleistocene demography can inform our understanding of global change
Temperate zone forest trees, ranging across broad geographic areas, have experienced drastic changes in climate and geographic distributions throughout the Quaternary. Spanning strong environmental gradients, local adaptation has become a defining feature. We investigated the genomic basis of adaptation and reconstructed the population history of a dominant riparian tree, Populus trichocarpa using 544 complete genome sequences and replicated common gardens.
We found strong genomic evidence of recent positive and/or divergent selection at loci that impact key adaptive traits, such as spring and fall phenology. Using a combination of genomic approaches to demographic analysis, we examined the species’ population dynamics prior to and following the Last Glacial Maximum, finding that the current distribution of genetic variation likely arose recently from several refugia with contrasting patterns of growth and contraction throughout the range. Regional gene flow, within P. trichocarpa and through introgression from other hybridizing Populus species, also influences patterns of genetic variation and adaptation. Together, these studies inform our understanding of how extant patterns of genetic variation arose – from a mix of standing variation, novel mutations, and introgression; rapid serial colonization of new habitat; and directional selection in large effective populations. In the face of global change, such knowledge will aid breeding and conservation efforts in ecologically and commercially important forest trees.