title: Evidence for extensive parallelism but divergent genomic architecture of adaptation along altitudinal and latitudinal gradients in Populus trichocarpa.
abstract: Adaptation to climate across latitude and altitude reflects shared climatic constraints, which may lead to parallel adaptation. However, theory predicts that higher gene flow should favor more concentrated genomic architectures, which would lead to fewer locally maladapted recombinants. We used exome capture to resequence the gene space along a latitudinal and two altitudinal transects in the model tree Populus trichocapra. Adaptive trait phenotyping was coupled with FST outlier tests and sliding window analysis to assess the degree of parallel adaptation as well as the genomic distribution of outlier loci. Up to 51% of outlier loci overlapped between transect pairs and up to 15% of these loci overlapped among all three transects. Genomic clustering of adaptive loci was more pronounced for altitudinal than latitudinal transects. In both altitudinal transects, there was a larger number of these 'islands of divergence', which were on average longer and included several of exceptional physical length. Our results suggest that recapitulation of genetic clines over latitude and altitude involves extensive parallelism, but that steep altitudinal clines generate islands of divergence. This suggests that physical proximity of genes in coadapted complexes may buffer against the movement of maladapted alleles from geographically proximal but climatically distinct populations.
authors.affiliation: Department of Forest Resources and Environmental Conservation, Virginia Polytechnic Institute and State University, 304 Cheatham Hall, Blacksburg, VA, 24061, USA.
authors.forename: Jason A
authors.initials: JA
authors.lastname: Holliday
authors.affiliation: Department of Forest Resources and Environmental Conservation, Virginia Polytechnic Institute and State University, 304 Cheatham Hall, Blacksburg, VA, 24061, USA.
authors.forename: Lecong
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Department of Forest Resources and Environmental Conservation, Virginia Polytechnic Institute and State University, 304 Cheatham Hall, Blacksburg, VA, 24061, USA.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Bawa
authors.affiliation: Department of Forest Resources and Environmental Conservation, Virginia Polytechnic Institute and State University, 304 Cheatham Hall, Blacksburg, VA, 24061, USA.
authors.forename: Man
authors.initials: M
authors.lastname: Zhang
authors.affiliation: Department of Forest Resources and Environmental Conservation, Virginia Polytechnic Institute and State University, 304 Cheatham Hall, Blacksburg, VA, 24061, USA.
authors.forename: Regis W
authors.initials: RW
authors.lastname: Oubida
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics*; D000531:Altitude; D016000:Cluster Analysis; D018899:CpG Islands / Q000235:genetics; D063990:Gene Ontology; D056426:Genetic Loci; D018745:Genome, Plant; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D032107:Populus / Q000235:genetics* / Q000502:physiology*
keywords: Populus trichocarpa; genomic architecture; local adaptation; parallel adaptation; sequence capture