Speciation-with-gene-flow; Admixture; Porous genome; Populus; Hybridization; Species barriers; Reproductive isolation; Evolutionary genomics
Christe C Stölting KN Paris M Fraisse C Bierne N & Lexer C (2017), Adaptive evolution and segregating load contribute to the genomic landscape of divergence in two tree species connected by episodic gene flow, in Molecular Ecology
, 26, 59-76.
Holliday JA Aitken SN Cooke JEK Fady B González-Martínez SC Heuertz M Jaramillo-Correa J-P Le (2017), Advances in ecological genomics in forest trees and applications to genetic resources conservation and breeding, in Molecular Ecology
, 26, 706-717.
David Macaya-Sanz Myriam Heuertz Dorothea Lindtke Giovanni G. Vendramin Christian Lexer Santiag (2016), Causes and consequences of large clonal assemblies in a poplar hybrid zone, in Molecular Ecology
, 25, 5330-5344.
Suarez-Gonzalez A Hefer CA Christe C Corea O Lexer C Cronk QCB & Douglas CJ (2016), Genomic and functional approaches reveal a case of adaptive introgression from Populus balsamifera (balsam poplar) in P. trichocarpa (black cottonwood), in Molecular Ecology
, 25, 2427-2442.
Christe C Stölting KN Bresadola L Fussi B Heinze B Wegmann D & Lexer C (2016), Selection against recombinant hybrids maintains reproductive isolation in hybridizing Populus species despite F1 fertility and recurrent gene flow, in Molecular Ecology
, 25, 2482-2498.
Caseys C Stritt C Glauser G Blanchard T & Lexer C (2015), Effects of hybridization and evolutionary constraints on secondary metabolites: the genetic architecture of phenylpropanoids in European Populus species, in PLoS ONE
, 10, e0128200.
Stölting KN Paris M Meier C Heinze B Castiglione S Bartha D & Lexer C (2015), Genome-wide patterns of differentiation and spatially varying selection between postglacial recolonization lineages of Populus alba (Salicaceae), a widespread forest tree, in New Phytologist
, 207, 723-734.
Caseys C Stölting KN Barbará T González-Martínez SC & Lexer C (2015), Patterns of genetic diversity and differentiation in resistance gene clusters of two hybridizing European Populus species, in Tree Genetics and Genomes
, 11, 81.
Lindtke D Gompert Z Lexer C & Buerkle CA (2014), Unexpected ancestry of Populus seedlings from a hybrid zone implies a large role for postzygotic selection in the maintenance of species, in Molecular Ecology
, 23, 4316-4330.
Adriana Suarez-Gonzalez Charles A. Hefer Christian Lexer Carl J. Douglas and Quentin C. B. Cronk, Introgression from Populus balsamifera underlies adaptation and range boundaries in P. trichocarpa, in New Phytologist
Rapid recent progress in ecological & evolutionary genomics is imparting fresh perspectives to the study of speciation, i.e. the origin and maintenance of biological diversity. A particularly active field of research at the current time is the study of ‘divergence with gene flow’ (DWGF), that is, divergence that involves episodes of sym- or parapatry and thus genetic contact during some stage of the process, before reproductive isolation is complete. A conceptual framework for DWGF has started to emerge, motivated by the increasing ease with which genomic data can now be collected in wild species using high throughput (HT) sequencing approaches. As a result, there are now testable predictions on the types of genetic architectures, genomic patterns of differentiation and linkage disequilibrium (LD), and the interplay of population genetic forces operating at each stage. These hypotheses are relevant to both speciation and the breakdown and potential resurgence of reproductive barriers upon secondary contact. To test these predictions, there is an urgent need to couple genomics with experiments.In this project I propose to combine population genomics with ecological and crossing experiments to address DWGF in Populus alba and P. tremula, two hybridizing, ecologically divergent (flood-plain vs. upland pioneer) members of the ‘model tree’ genus Populus, including recombinant hybrids formed between them (P. x canescens). Recent evolutionary genomics work in my lab indicates ongoing DWGF in this group, with great variation in genetic divergence and hybrid ancestry across the genome, and this sets the stage for the present project. The proposed work is structured into three clearly defined steps.First, we will use HT genotyping-by-sequencing approaches to study open pollinated progeny arrays of these species and hybrids planted in a reciprocal common garden trial. This will allow us to test key hypotheses regarding (a) the role of early- vs. late-acting barriers in the maintenance of species boundaries, (b) the fine-scale genomic architecture of species differences maintained in these ecologically divergent species in the face of gene flow, (c) the contribution of divergent selection and drift to the maintenance of RI. Second, we will study controlled crosses with the same HT genotyping methods to test the role of meiotic drive, cyto-nuclear incompatibilities, and other early post-mating barriers in maintaining species boundaries. Third, we will extend our recent population genomics work of these species from Europe to Asia to examine intraspecific variation for genomic isolation, which may arise due to variation in isolation genes or divergent selection associated with environmental differences at this greatly extended geographic scale.The results of all three objectives will be mapped onto available Populus genome assemblies to yield a picture and synthesis of the genomic architecture of isolation for these ‘model forest tree’ taxa with unprecedented breadth and depth, and the results will be published and available to the Populus and wider evolutionary genomics communities, natural resource managers and breeders. The evolutionary genomics of speciation and species boundaries represents one of the most hotly debated topics in biology. By coupling genomics with experiments, we will significantly advance our understanding of these important topics in native tree species representing keystone or foundation species in terrestrial habitats.