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.