Linking phenotype, genotype and environment to unravel genetic components underlying cold hardiness in coastal Douglas-fir (Pseudotsuga menziesii var. menziesii)

Global climate change may detrimentally affect future generations of numerous forest tree species, hampering their long-term sustainability if appropriate evolutionary responses remain lacking. To face these novel threats, conservation biologists are in need of a thorough understanding and identification of adaptive variation in key fitness traits. We here provide an elaborate synthesis of pre-existing and novel analyses of an association mapping, genecological and landscape genomic study integrating genotypic, environmental and phenotypic data to gain insights into the genetic basis of cold-hardiness adaptation in coastal Douglas-fir (Pseudotsuga menziesii var. menziesii). Data were collected across part of the natural range for a total of 643 individuals. A landscape genomic approach revealed 28 putative non-neutral genes, although a variance partitioning analysis indicated only moderate power of this gene set in explaining cold-hardiness-related phenotypic variation, and suggests many important genes await discovery. Integrating these results within the entire phenotype-genotype-environment spectrum allowed us to delineate the six most promising candidate genes under selection. By combining genomic, phenotypic and environmental data, this study attempts to gain insights in the genetic basis of key adaptations, which may ultimately aid forestry managers to establish resilient ecosystems in face of future climate change.