A forest dark : an evolutionary history of Norway spruce

Embedded within the relationships among species is a dense forest of gene trees, each with a potentially unique and discordant history. Such widespread genealogical heterogeneity is expected, but embracing this hierarchy of discordance while reconstructing the histories of populations and species remains a major challenge. In this thesis, I studied the history of the genes and genomes contained within Norway spruce (Picea abies: Pinaceae), a forest tree distributed throughout boreal and montane Europe. I sequenced plastid genomes from all the commonly-recognized Picea species and developed a novel strategy to assemble the bacterial-sized mitochondrial genome of Norway spruce. Using multispecies coalescent network models, I reconstructed the relationships among populations of Norway spruce and the parapatric Siberian spruce (P. obovata) and distinguished between drift and hybridization as sources of phylogenetic discord. Norway spruce holds heterogenous histories at multiple levels of organization. Although organelle genomes are expected to be clonal and uniparentally inherited, the chloroplast genome held by Norway spruce originated after sexual recombination between two divergent lineages. In the mitochondrial genome, recombination creates a diverse population of genome arrangements subjected to drift and selection within individuals and populations. Genetic diversity among populations is shaped in nearly equal measure by divergence and hybridization. Norway spruce is discordance distilled