Population Genetics and Genome Organization of Norway Spruce

Abstract: Understanding the underlying genetic causes of adaptation to local conditions is one of the main goals of population genetics. A strong latitudinal cline in the phenotypic trait of bud set is observed in present day populations of Norway spruce (Picea abies (L.) Karst). The first step towards determining how this strong selection on adaptive traits translates at the loci underlying the trait was to use multilocus sequence data to gain information on the fundamental population genetic properties of Norway spruce. We determined that the level of LD was low and genetic diversity was in the low range. Coalescent simulations revealed a demographic scenario of a fairly old and severe bottleneck as consistent with the observed data. To examine the role of selection at genes putatively involved in the control of bud set we, again, used a multilocus data set to test for deviations from neutrality and demographic scenarios inferred from background loci. Different candidate genes were identified by using different approaches, highlighting the difficulty in predicting how local adaptation will manifest itself on different time scales and in rangewide samples. When examining properties important in the design of association studies, the inevitable next step in identifying genes involved in local adaptation, we found that previous estimates of a low level of LD were highly influenced by the joint analysis of several loci over a large distribution range and that estimates of LD was in fact heterogeneous across loci and increased within populations. In addition, we found that within species tests for deviations from neutral expectations were highly sensitive to sample size. Additional genomic sequence characterization in Norway spruce is necessary to provide more comprehensive sets of markers for association studies, also including gene promoters and non-genic regions of the genome. In the final paper we show that the HMPR method is effective in constructing libraries enriched for the single copy fraction of the genome when applied to the large and dominantly repetitive genome of Norway spruce.In summary, the studies presented in this thesis together constitute a foundation for future studies on adaptive evolution in Norway spruce.