Ancient vicariance is reinforced by adaptive divergence in the southern beech: Contributions from geogenomics

FASANELLA, MARIANA; MATHIASEN PAULA; JURI GABRIELA; DÍAZ DAYANA; HASBÚN RODRIGO; ANDREA CECILIA PREMOLI

JOURNAL OF BIOGEOGRAPHY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2022

0305-0270

Aim: Geogenomics seeks to understand geological processes linked to lineage divergence.However, the mechanisms that conserve ancient signals in spite of gene floware still unclear. In the southern beech, the deep lineage divergence produced by vicariantevents is associated with ancient marine transgressions. We hereby evaluatethe hypothesis that this divergence is maintained by diversifying selection.Location: Southern Argentina and Chile.Taxon: Nothofagus dombeyi.Methods: The lineage divergence by means of analysis of molecularvariance (AMOVA), principal coordinate analysis, assignment tests and multiple matrixregression analyses were assessed using chloroplast DNA and neutral and outliersingle nucleotide polymorphisms (SNPs). Several environmental variables were usedto characterize potential within-speciesniche structuring and genotype–environmentassociations.Results: Two deep-rootedlatitudinally structured lineages resulted from cpDNA, thenorthern cluster being more genetically diverse than the southern one. Of the totalof 2943 SNPs, 33 identified as outliers and produced two genetic clusters. NeutralSNPs yielded no structure by AMOVA, whereas higher (>75%) FST values were obtainedfor cpDNA and outlier SNPs. Precipitation variables were mostly associatedwith population clusters and suggested two climatic niches, consisting of cold and dryin the south and more variable precipitation, temperature and soil conditions in thenorth. Associations of genetic distance with environment and geography suggestedisolation-by-distanceand isolation-by-ecologyor isolation-by-environmenteffects.Main conclusions: Ancient lineage divergence in N. dombeyi, originally driven by vicariance,has been maintained by diversifying selection under distinct environmentalconditions that also define distinct within-speciesniches. Deeply rooted phylogeographicalbreaks can be conserved in continuously distributed species in the absenceof current geographical barriers. Yet, physical gradients exert differential selectivepressures, which are maintained in the face of potential gene flow. As a result, selectioncan lead to geographically localized and differentially adapted groups of populationsthat can be detected by a combination of traditional phylogeographical andnovel genomic methods.