Local Adaptation in the Interior Spruce Hybrid Complex

Abstract

Interior spruce is a hybrid species complex composed of white spruce, Engelmann spruce, and their hybrids, distributed across a wide area in western Canada. In both interior spruce and allopatric white spruce, half a century of study on local adaptation to climate has been complemented by a large number of genomic studies within the past decade. This chapter reviews the genomic evidence for local adaptation in interior spruce and allopatric white spruce, comparing the results gleaned from these studies with phenotypic studies when possible. In interior spruce, genomic and phenotypic studies have consistently identified local adaptation to cold temperatures, particularly through autumn cold hardiness, with mixed results for other traits and climatic variables. Studies in allopatric white spruce have found variable evidence for local adaptation, with genomic studies largely finding clinal variation with mean annual temperature. Several genomic approaches have been used to infer local adaptation in this species complex, and these have often found contrasting patterns of adaptation between allopatric white spruce and interior spruce, and weak correlation between genetic markers identified across multiple studies. While genomic and phenotypic analyses are often complementary, novel genomic approaches have also been applied to understand aspects of local adaptation that are difficult or impossible to measure exclusively phenotypically, including hybrid fitness, the genetic architectures of adaptive traits, and phenotypic plasticity.