Genome-wide shifts in climate-related variation underpin responses to selective breeding in a widespread conifer MacLachlan, Ian; McDonald, Tegan; Lind, Brandon; Rieseberg, Loren; Yeaman, Samuel; Aitken, Sally
Locally adapted temperate tree populations exhibit genetic trade-offs among climate-related traits that can be exacerbated by selective breeding, and are challenging to manage under climate change. To inform climatically adaptive forest management, we investigated the genetic architecture and impacts of selective breeding on four climate-related traits in 105 natural and 20 selectively bred lodgepole pine populations from western Canada. Growth, cold injury and growth initiation and growth cessation phenotypes were tested for associations with 18,600 SNPs in natural populations to identify ‘positive effect alleles’ (PEAs). The effects of artificial selection for faster growth on PEA frequencies for each trait were quantified in breeding populations from different climates.
Substantial shifts in PEA proportions and frequencies were observed across many loci after two generations of selective breeding for height, and responses of phenology-associated PEAs differed strongly among climatic regions. Extensive genetic overlap was evident among traits. Alleles most strongly associated with greater height were often also associated with greater cold injury and delayed phenology, although it is unclear whether potential trade-offs arose directly from pleiotropy or indirectly via genetic linkage. Modest variation among populations in PEA frequencies across many loci was associated with large phenotypic differences and strong climatic gradients, providing support for assisted gene flow polices. Relationships among genotypes, phenotypes and climate in natural populations were maintained or strengthened by selective breeding. However, future adaptive phenotypes and assisted gene flow may be compromised if selective breeding further increases the PEA frequencies of SNPs involved in adaptive trade-offs among climate-related traits.; Usage notes
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