Disentangling the roles of history and local selection in shaping clinal variation of allele frequencies and gene expression in Norway spruce (Picea abies)

Understanding the genetic basis of local adaptation is challenging due to the subtle balance among conflicting evolutionary forces that are involved in its establishment and maintenance. One system with which to tease apart these difficulties are clines in adaptive characters. Here we analyzed genetic and phenotypic variation in bud set, a highly heritable and adaptive trait, among 18 populations of Norway spruce (Picea abies), arrayed along a latitudinal gradient ranging from 47°N to 68°N. We confirmed that variation in bud set is strongly clinal using a subset of five populations. Genotypes for 137 single nucleotide polymorphisms (SNPs) chosen from 18 candidate genes putatively affecting bud set, and 308 control SNPs chosen from 264 random genes, were analyzed for patterns of genetic structure and correlation to environment. Population genetic structure was low (FST = 0.05), but latitudinal patterns were apparent among Scandinavian populations. Hence, part of the observed clinal varia...