Molecular Signatures of Adaptation and Selection in Forest Trees

Abstract

Abstract Uncovering the genes and molecular basis of phenotypic variation and adaptation is a major goal in conservation and evolutionary genetics; it also sets the basis for future operational breeding in commercial species, like forest trees. These taxa are characterized by their large size, growth habit and longevity, which hampers the use of reverse-genetic approaches (i.e. from gene function to phenotype) to pinpoint adaptive molecular variants. In this chapter, we summarize the basis of the forward-genetic approaches (i.e. from phenotype to gene function) currently used in forest trees. For each strategy, we provide a brief overview of the statistical approaches employed to identify candidate genes, and then highlight the main findings of landmark studies that provide evidence for adaptation in forest trees. Adaptive and commercial traits are generally well inherited in trees, although they are mostly affected by the variation of multiple genes, each one accounting for a small part of the phenotypic variance of each character. However, some individual and important genes involved in growth, phenology, drought resistance and cold hardiness have been identified; many of them showing evidence of selection across multiple taxa (sometimes including angiosperms and gymnosperms). Future challenges for detecting the signatures and understanding the molecular basis of adaptation in trees include more adequate and precise phenotype assessment in natural populations, and the inclusion of gene interactions and epigenetic variations in current models. The implications of these findings in conservation and breeding of forest trees are finally discussed.