Adaptations to Northern Wintering Conditions
The two main wintering stressors on Sitka spruce are increased pressure involved with snowfall and freezing. Northern conifers already have conserved adaptions to snowfall, with homeotic genes conferring a triangular form factor and thin needles to reduce the build-up of snow (Du et al., 2020; Uddenberg et al., 2015). Here we identified a reduction in size as a major adaption to snowfall. The high minor allele frequency of these adaptive alleles indicates recent local adaptions. This is clear in the geographic distribution of these alleles with northern populations having more alleles negatively affecting height. From the co-association analysis, we see the traits associated with freezing grouping together as cluster 3. These traits are temperature seasonality and minimum, maximum and mean snow cover. From the CANCOR analysis we see a negative correlation between height and these freezing traits.