Evolutionary genomics; Populus; Adaptive introgression; Reproductive isolation; Ecological divergence; Selective sweep; Local adaptation; Porous genome; speciation; selection; gene flow; recombination; hybrid zone
(2013), Admixture mapping of quantitative traits in Populus hybrid zones: power and limitations, in Heredity
, advance online, 1.
(2013), Genomic scan for single nucleotide polymorphisms reveals patterns of divergence and gene flow between ecologically divergent species, in MOLECULAR ECOLOGY
, 22(3), 842-855.
(2012), Effects of interspecific recombination on functional traits in trees revealed by metabolomics and genotyping-by-resequencing, in PLANT ECOLOGY & DIVERSITY
, 5(4), 457-471.
(2012), Recombinant hybrids retain heterozygosity at many loci: new insights into the genomics of reproductive isolation in Populus, in MOLECULAR ECOLOGY
, 21(20), 5042-5058.
(2012), Whole genome sequencing (WGS) meets biogeography and shows that genomic selection in forest trees is feasible, in NEW PHYTOLOGIST
, 196(3), 652-654.
(2011), Genetic analysis of post-mating reproductive barriers in hybridizing European Populus species, in HEREDITY
, 107(5), 478-486.
(2011), Tracing the recombination and colonization history of hybrid species in space and time, in MOLECULAR ECOLOGY
, 20(18), 3701-3704.
(2010), Conservation Genomics, 349-368.
(2010), Genomic Admixture Analysis in European Populus spp. Reveals Unexpected Patterns of Reproductive Isolation and Mating, in GENETICS
, 186(2), 699-699.
(2010), Polymorphism of postmating reproductive isolation within plant species, in TAXON
, 59(5), 1367-1374.
, ‘Next generation’ biogeography: towards understanding the drivers of species diversification and persistence, in Journal of Biogeography
Reproductive barriers between species often do not conform to the idea of ‘whole genome isolation’. Rather, in many organismal groups such as birds, fishes, insects, and plants, divergent populations or species exhibit ‘porous’ genomes, implying that reproductive isolation often has a genic basis and can be studied with genetic tools. This ‘genic view’ of speciation and species evolution has driven rapid recent progress in speciation genomics, i.e. research on the mechanisms that generate and maintain biological diversity and adaptive differences in nature.A very little understood aspect of the porous genome is the full impact of porous species barriers on the evolution of functionally relevant variation within species. Predictions from theoretical models have so far been tested only in a small number of model organisms, and even there many important questions remain open. These include questions regarding the actual genetic mechanisms underlying species isolation (e.g. underdominance vs. negative epistasis), the functional role and nature of isolation genes (e.g. intrinsic or ecological), and questions regarding the genomic patterns of recombination that structure porous genomes into ‘genomic islands’ of divergence on the one hand, and into movable, introgression-prone regions on the other. We also know little to nothing about the proportion of introgressed genes that spread within the recipient species’ ranges due to positive selection.In this project I propose to address these topics for Populus alba and P. tremula, two hybridizing, ecologically divergent (flood-plain vs. upland pioneer) forest trees with wide overlapping geographic ranges across Europe. Recent and ongoing work in my lab indicates the presence of a wide range of recombinant genotypes in multiple localities where these species hybridize. This sets the stage for the present project by providing the opportunity to study a large number of well characterized genes potentially involved in species isolation and adaptive introgression. The proposed work is structured into three clearly defined steps.In the first step, we will use high-throughput sequencing of short DNA amplicons to develop molecular genetic markers (SNPs and microsatellites) in or near 250 expressed genes with known functional roles in flooding tolerance, phenology, and plant defence, the latter including clusters of pathogen resistance genes near the sex determination locus. The results will contribute to a genome-wide ‘divergence map’ for these two species and help clarify the role of the sex determining region in species isolation. In the second step, we will examine ‘genomic clines’ for each gene or gene-cluster in two hybrid zone ‘replicates’ to identify loci involved in species isolation on the one hand, and candidate loci for adaptive introgression on the other. In the same step, we will track polymorphisms in each gene in up to eight para- or allopatric populations of P. alba to determine the minimum number of introgressed genes that spread across the Western portion of the species’ range. In the third step, we will characterize top candidate loci for species isolation and adaptive introgression by analyzing full-length sequences and by assaying polymorphisms in nearby genes. This will allow us to evaluate patterns of diversity and linkage disequilibrium (LD) surrounding these non-neutral polymorphisms.The evolutionary genomics of speciation and species boundaries represents one of the most hotly debated topics in biology. Through its focus on two native European forest trees, the project will contribute significantly to our understanding of the origin and evolution of functionally relevant biodiversity in keystone or foundation species in terrestrial habitats. Information about DNA variants in ecologically important genes and their introgression across species barriers will be accessible by breeders, forest management and conservation bodies such as those collaborating on this project, thus the practical usefulness of the results is certain.