Climate shapes tree genetics across Scandinavia, study reveals
Researchers found that three major boreal tree species in Sweden have evolved distinct genetic patterns along climate boundaries, despite growing from the same post-glacial origins. The discovery suggests that forestry management and breeding programs may need region-specific strategies to maintain forest health as climate pressures intensify.
Originaltitel: When South Meets North: A Joint Contact Zone Coinciding With Environmental Gradients in Three Boreal Tree Species
<p>Post-glacial recolonisation of Fennoscandia created secondary contact zones in many species, offering opportunities to study how gene flow and selection contribute to their establishment and maintenance. Here, we analyse genomic data from three boreal tree species-<em>Picea abies, Betula pendula</em> and <em>Pinus sylvestris</em>-sampled along a latitudinal gradient in Sweden. Despite differences in colonisation timing and dispersal ecology, all three species exhibit north-south genetic structuring aligned with environmental gradients. Most notably, the two main genetic clusters within each species overlap in a shared contact zone, corresponding to the climatic transition between Sweden's two major environmental zones. The extent and structure of the contact zone differ among species: <em>P. abies </em>shows stronger genetic structure and moderate gene flow, <em>B. pendula </em>exhibits intermediate differentiation and gene flow, and <em>P. sylvestris</em> displays the weakest structure with stronger gene flow. All three species also show genomic signatures of local adaptation, with distinct underlying architectures. In <em>P. abies</em>, adaptive loci are broadly distributed across the genome, while, strikingly, they are mostly found within an inversion on chromosome 1 in <em>B. pendula</em>. In <em>P. sylvestris</em>, local adaptation likely relies on subtle allele frequency shifts across many loci with weak signals. These patterns align with theoretical expectations for polygenic local adaptation under varying migration regimes. Our comparative approach demonstrates how gene flow and selection jointly shape genomic landscapes in shared environments and contribute to understanding local adaptation in forest trees, with implications for predicting species' responses to climate change.</p>