Recent introductions, ancient recolonization events and local adaptation: a first fine-scale mapping of the population genetic structure of Norway spruce across Sweden

• Population genetic structure matters for a large range of issues: it is intrinsically related to speciation and local adaptation, it informs us on past demography, it conditions the response of populations to climate change or to the spread of diseases and it severely limits the power of genome wide association studies (GWAS). In the present study we genotyped all individuals from the base population of the Swedish P. abies breeding program using exome capture. In total 4769 individuals were genotyped. This very large and dense sampling along a latitudinal gradient ranging from 55°N to 67°N, together with a large number of polymorphisms (>300,000 SNPs) allowed us to analyze population genetic structure at an unprecedented scale and to test for associations between genetic polymorphisms and environmental variables We used clustering methods (PCA, Admixture) to obtain a first genetic clustering of the data. Moreover, in order to better capture the mixture of discrete and continuous processes that generated the distribution of the genetic variation of Norway spruce across Sweden two recently developed spatialized analyses (conStruct, EEMS) were also performed. The overall data comprises both trees of Swedish origin and a large number of trees recently introduced into Sweden from the rest of the range and is highly structured with a total of six clusters representing the main postglacial refugia and admixed populations originating from the refugia. Focusing on the trees of Swedish origin, the data shows that those can be divided into two main clusters with a contact zone in central Sweden and a third small cluster in northern Sweden. The contact zone is also observed in other species and likely reflects the meeting point of the two main waves of recolonization of Scandinavia after the Last Glacial Maximum. As to the northernmost cluster it was characterized by a high contribution from P. obovata. A large number of SNPs were found to be associated to environmental variables and exhibited a stronger pattern of isolation-by-distance than random SNP. Considering that P. abies has been in Sweden for less than 50 generations, this suggests a strong selection pressure during the expansion of the species through Scandinavia. 

Subject headings

NATURVETENSKAP  -- Biologi -- Evolutionsbiologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Evolutionary Biology (hsv//eng)

NATURVETENSKAP  -- Biologi -- Genetik (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Genetics (hsv//eng)

Keyword

Evolutionary Genetics

Evolutionär genetik

Evolutionary Genetics

Evolutionär genetik

Biology with specialization in Evolutionary Genetics

Biologi med inriktning mot evolutionär genetik

Publication and Content Type

vet (subject category)

ovr (subject category)