Biology subjects

Rougemont, Q.

Publications and source records attributed to Rougemont, Q..

At least 19 recordsLinked to original sources

bioRxiv2026

A mosaic of genomic architectures underpins parasitism loss in a jawless vertebrate

Lampreys are the only ancestrally parasitic vertebrate lineage, yet parasitism has been repeatedly lost alongside a suite of life-history changes, such as loss of migration and juvenile feeding and accelerated maturation. Combining whole-genome resequencing, haplotype-resolved assemblies, hybrid-zone genotyping, multi-tissue transcriptomics, and sperm phenotyping, we map this life-history syndrome in European Lampetra to six chromosomes spanning a mosaic of genomic architectures: a [~]20 Mb low-recombination region on chromosome 1 lacking chromosomal rearrangements within Lampetra but involving inter-specific rearrangements across deep lamprey lineages; a translocated inversion with ecotype-dependent sperm-velocity effects; and ecotype-divergent deletions overlapping genes crucial for nervous system (CNTNAP2) and reproductive development (FSHR). However, this genomic basis is not shared with a convergent sister lineage, pointing to independent routes to a recurring life-history transition in lampreys.

evolutionary biology↗

bioRxiv2025

EASYstrata: a new workflow to infer evolutionary strata along sex chromosomes and other supergenes

New reference genomes and transcriptomes are increasingly available across the tree of life, opening new avenues to tackle exciting questions. However, there are still challenges associated with annotating genomes and inferring evolutionary processes and with a lack of methodological standardisation. Here, we propose a new workflow designed for evolutionary analyses to overcome these challenges, facilitating the detection of recombination suppression and its consequences in terms of rearrangements and transposable element accumulation. To do so, we assemble multiple bioinformatic steps in a single easy-to-use workflow. We combine state-of-the-art tools to detect transposable elements, annotate genomes, infer gene orthology relationships, compute divergence between sequences, infer evolutionary strata (i.e., footprints of stepwise extension of recombination suppression) and their structural rearrangements, and visualise the results. This workflow, called EASYstrata, was applied to reannotate 42 published genomes from Microbotryum fungi. We show in further case examples from a plant and an animal that we recover the same strata as previously described. While this tool was developed with the goal to infer divergence between sex or mating-type chromosomes, it can be applied to any pair of haplotypes whose patteern of divergence is of interest. This workflow will facilitate the study of non-model species for which newly sequenced phased diploid genomes are becoming available. Contactquentinrougemont@orange.fr

genomics↗

bioRxiv2024

Million years old recombination suppression and balancing selection in a region linked to the mating-type locus in the invasive chestnut blight fungal pathogen Cryphonectria parasitica

Recombination suppression can evolve in sex or mating-type chromosomes, or in autosomal supergenes, with different haplotypes being maintained by balancing selection. In the invasive chestnut blight fungus Cryphonectria parasitica, a genomic region was suggested to lack recombination and to be partially linked to the mating-type (MAT) locus based on segregation analyses. Using hundreds of available C. parasitica genomes and generating new high-quality genome assemblies, we show that a ca. 1.2 Mb genomic region proximal to the mating-type locus lacks recombination, with the segregation of two highly differentiated haplotypes in balanced proportions in invasive populations. High-quality genome assemblies further revealed an inversion in one of the haplotypes in the invaded range. The two haplotypes were estimated to have diverged 1.5 million years ago, and each harboured specific genes, some of which likely belonging to Starship elements, that are large mobile elements, mobilized by tyrosine recombinases, able to move accessory genes, and involved in adaptation in multiple fungi. The MAT-proximal region carried genes upregulated under virus infection or vegetative incompatibility reaction. In the native range, the MAT-proximal region also appeared to have a different evolutionary history than the rest of the genome. In all continents, the MAT-Proximal region was enriched in non-synonymous substitutions, in gene presence/absence polymorphism, in tyrosine recombinases and in transposable elements. This study thus sheds light on a case of a large non-recombining region partially linked to a mating compatibility locus, with likely balancing selection maintaining differentiated haplotypes, possibly involved in adaptation in a devastating tree pathogen.

evolutionary biology↗

bioRxiv2024

Repeated loss of function at HD mating-type genes and of recombination suppression without mating-type locus linkage in anther-smut fungi

A wide diversity of mating systems occur in nature, with frequent evolutionary transitions in mating-compatibility mechanisms. Basidiomycete fungi typically have two mating-type loci controlling mating compatibility, HD and PR, usually residing on different chromosomes. In Microbotryum anther-smut fungi, there have been repeated events of linkage between the two mating-type loci through chromosome fusions, leading to large non-recombining regions. By generating high-quality genome assemblies, we found that two sister Microbotryum species parasitizing Dianthus plants, M. superbum and M. shykoffianum, as well as the distantly related M. scorzonarae, have their HD and PR mating-type loci on different chromosomes, but with the PR mating-type chromosome fused with part of the ancestral HD chromosome. Furthermore, progressive extensions of recombination suppression have generated evolutionary strata. In all three species, rearrangements suggest the existence of a transient stage of HD-PR linkage by whole chromosome fusion, and, unexpectedly, the HD genes lost their function. In M. superbum, multiple natural diploid strains were homozygous, and the disrupted HD2 gene was hardly expressed. Mating tests confirmed that a single genetic factor controlled mating compatibility (i.e. PR) and that haploid strains with identical HD alleles could mate and produce infectious hyphae. The HD genes have therefore lost their function in the control of mating compatibility in these Microbotryum species. While the loss of function of PR genes in mating compatibility has been reported in a few basidiomycete fungi, these are the first documented cases for the loss of mating-type determination by HD genes in heterothallic fungi. The control of mating compatibility by a single genetic factor is beneficial under selfing and can thus be achieved repeatedly, through evolutionary convergence in distant lineages, involving different genomic or similar pathways.

evolutionary biology↗

bioRxiv2023

The Silene latifolia genome and its giant Y chromosome

In some species, the Y is a tiny chromosome but the dioecious plant Silene latifolia has a giant [~]550 Mb Y chromosome, which has remained unsequenced so far. Here we used a hybrid approach to obtain a high-quality male S. latifolia genome. Using mutants for sexual phenotype, we identified candidate sex-determining genes on the Y. Comparative analysis of the sex chromosomes with outgroups showed the Y is surprisingly rearranged and degenerated for a [~]11 MY-old system. Recombination suppression between X and Y extended in a stepwise process, and triggered a massive accumulation of repeats on the Y, as well as in the non-recombining pericentromeric region of the X, leading to giant sex chromosomes. One-Sentence SummaryThis work uncovers the structure, function, and evolution of one of the largest giant Y chromosomes, that of the model plant Silene latifolia, which is almost 10 times larger than the human Y, despite similar genome sizes.

genomics↗

bioRxiv2022

Subtle introgression footprints at the end of the speciation continuum in a clade of Heliconius butterflies

Quantifying gene flow between lineages at different stages of the speciation continuum is central to understanding speciation. Heliconius butterflies have undergone an adaptive radiation in wing colour patterns driven partly by natural selection for local mimicry. Colour patterns are also known to be used as assortative mating cues. Therefore, wing pattern divergence is considered to play a role in speciation. A corollary is that mimicry between closely-related species may be associated with hybridization and interfere with reproductive isolation. Here, we take a multifaceted approach to explore speciation history, species boundaries, and traits involved in species differentiation between the two closely-related species H. hecale and H. ismenius. We focus on geographic regions where the two species mimic each other, and contrast this with geographic regions where they do not mimic each other. To examine population history and patterns of gene flow, we tested and compared a four-population model accounting for linked selection. This model suggests that the two species have remained isolated for a large part of their history, yet with a small amount of gene exchange. Accordingly, signatures of genomic introgression were small except at a major wing pattern allele and chemosensing genes, and stronger in the mimetic populations compared to non-mimetic populations. Behavioural assays confirm that visual confusion exists but that short-range cues determine strong sexual isolation. Tests for chemical differentiation between species identified major differences in putative pheromones which likely mediate mate choice and the maintenance of species differences.

evolutionary biology↗

bioRxiv2022

Allele surfing causes maladaptation in a Pacific salmon of conservation concern

How various factors, including demography, recombination or genome duplication, may impact the efficacy of natural selection and the burden of deleterious mutations,is a central question in evolutionary biology and genetics. In this study, we show that key evolutionary processes, including variations in i) effective population size (Ne) ii) recombination rates and iii) chromosome inheritance, have influenced the genetic load and efficacy of selection in Coho salmon (Oncorhynchus kisutch), a widely distributed salmonid species on the west coast of North America. Using whole genome resequencing data from 14 populations at different migratory distances from their southern glacial refugium, we found evidence supporting gene surfing, wherein reduced Ne at the postglacial recolonization front, leads to a decrease in the efficacy of selection and a surf of deleterious alleles in the northernmost populations. Furthermore, our results indicate that recombination rates play a prime role in shaping the load along the genome. Additionally, we identified variation in polyploidy as a contributing factor to within-genome variation of the load. Overall, our results align remarkably well with expectations under the nearly neutral theory of molecular evolution. We discuss the fundamental and applied implications of these findings for evolutionary and conservation genomics. Author SummaryUnderstanding how historical processes, such as past glaciations, may have impacted variations in population size and genetic diversity along the genome is a fundamental question in evolution. In this study, we investigated how recent postglacial demographic expansion has affected the distribution of deleterious genetic variants and the resulting deleterious mutation load in Coho salmon (Oncorhynchus kisutch), throughout its native range in North America. By sequencing the entire genome of 71 Coho salmon, we reveal that postglacial expansion has led to allele surfing, a process where alleles increase in frequency in populations that are expanding or colonizing new environments. Here, allele surfing resulted in an increased deleterious mutation load at the colonization front. Furthermore, we demonstrated that the efficacy of natural selection scales with variation in effective population size among populations. We showed that the specific genomic features of Coho salmon, namely variation in local recombination rate and variation in chromosomal inheritance, strongly impacted the segregation of deleterious mutations.

evolutionary biology↗

bioRxiv2022

Isolation-by-distance and population-size history inferences from the coho salmon (Oncorhynchus kisutch) genome

Coho salmon (Oncorhynchus kisutch) are a culturally and economically important species that return from multiyear ocean migrations to spawn in rivers that flow to the Northern Pacific Ocean. Southern stocks of coho salmon have significantly declined over the past quarter century, and unfortunately, conservation efforts have not reversed this trend. To assist in stock management and conservation efforts, we generated two chromosome-level genome assemblies and sequenced 24 RNA-seq libraries to better annotate the coho salmon genome assemblies. We also resequenced the genomes of 83 coho salmon across their North American range to identify nucleotide variants, characterize the broad effects of isolation-by-distance using a genome-wide association analysis approach, and understand the demographic histories of these salmon by modeling population size from genome-wide data. We observed that more than 13% of all SNPs were associated with latitude (before multiple test correction), likely an affect of isolation-by-distance. From demographic history modeling, we estimated that the SNP latitudinal gradient likely developed as recently as 8,000 years ago. In addition, we identified four genes each harboring multiple SNPs associated with latitude; all of these SNPs were also predicted to modify the function of the gene. Three of these genes have roles in cell junction maintenance and may be involved in osmoregulation. This signifies that ocean salinity may have been a factor influencing coho salmon recolonization after the last glaciation period - generating the current pattern of variation in these three genes.

genomics↗

bioRxiv2021

Population genetics reveals cryptic lineages and ongoing hybridization in a declining migratory fish species complex

Deciphering the effects of historical and recent demographic processes responsible for the spatial patterns of genetic diversity and structure is a key objective in evolutionary and conservation biology. Using population genetic analyses, we investigated the demographic history, the contemporary genetic diversity and structure, and the occurrence of hybridization and introgression of two species of anadromous fish with contrasting life history strategies and which have undergone recent demographic declines, the allis shad (Alosa alosa) and the twaite shad (Alosa fallax). We genotyped 706 individuals from 20 rivers and 5 sites at sea in Southern Europe at thirteen microsatellite markers. Genetic structure between populations was lower for the nearly semelparous species A. alosa, which disperses greater distances compared to the iteroparous species, A. fallax. Individuals caught at sea were assigned at the river level for A. fallax and at the region level for A. alosa. Using an approximate Bayesian computation framework, we inferred that the most likely long term historical divergence scenario between both species and lineages involved historical separation followed by secondary contact accompanied by strong population size decline. Accordingly, we found evidence for contemporary hybridization and bidirectional introgression due to gene flow between both species and lineages. Moreover, our results support the existence of at least one distinct species in the Mediterrannean sea: A. agone in Golfe du Lion area, and another divergent lineage in Corsica. Overall, our results shed light on the interplay between historical and recent demographic processes and life history strategies in shaping population genetic diversity and structure of closely related species. The recent demographic decline of these species populations and their hybridization should be carefully considered while implementing conservation programs.

evolutionary biology↗

bioRxiv2021

Long distance migration is a major factor driving local adaptation at continental scale in Coho Salmon

Inferring the genomic basis of local adaptation is a long-standing goal of evolutionary biology. Beyond its fundamental evolutionary implications, such knowledge can guide conservation decisions for populations of conservation and management concern. Here, we investigated the genomic basis of local adaptation in the Coho salmon (Oncorhynchus kisutch) across its entire North American range. We hypothesized that extensive spatial variation in environmental conditions and the species homing behavior may promote the establishment of local adaptation. We genotyped 7,829 individuals representing 217 sampling locations at more than 100,000 high-quality RADseq loci to investigate how recombination might affect the detection of loci putatively under selection and took advantage of the precise description of the demographic history of the species from our previous work to draw accurate population genomic inferences about local adaptation. Results indicated that genetic differentiation scans and genetic-environment association analyses were both significantly affected by variation in recombination rate as low recombination regions displayed an increased number of outliers. By taking these confounding factors into consideration, we revealed that migration distance was the primary selective factor driving local adaptation and partial parallel divergence among distant populations. Moreover, we identified several candidates SNP associated with long distance migration and altitude including a gene known to be involved in adaptation to altitude in other species. The evolutionary implications of our findings are discussed along with conservation applications.

evolutionary biology↗

bioRxiv2020

Copy number variants outperform SNPs to reveal genotype-temperature association in a marine species

Copy number variants (CNVs) are a major component of genotypic and phenotypic variation in genomes. To date, our knowledge of genotypic variation and evolution has largely been acquired by means of single nucleotide polymorphism (SNPs) analyses. Until recently, the adaptive role of structural variants (SVs) and particularly that of CNVs has been overlooked in wild populations, partly due to their challenging identification. Here, we document the usefulness of Rapture, a derived reduced-representation shotgun sequencing approach, to detect and investigate copy number variants (CNVs) alongside SNPs in American lobster (Homarus americanus) populations. We conducted a comparative study to examine the potential role of SNPs and CNVs in local adaptation by sequencing 1,141 lobsters from 21 sampling sites within the southern Gulf of St. Lawrence, which experiences the highest yearly thermal variance of the Canadian marine coastal waters. Our results demonstrated that CNVs accounts for higher genetic differentiation than SNP markers. Contrary to SNPs, for which no significant genetic-environment association was found, 48 CNV candidates were significantly associated with the annual variance of sea surface temperature, leading to the genetic clustering of sampling locations despite their geographic separation. Altogether, we provide a strong empirical case that CNVs putatively contribute to local adaptation in marine species and unveil stronger spatial signal of population structure than SNPs. Our study provides the means to study CNVs in non-model species and highlights the importance of considering structural variants alongside SNPs to enhance our understanding of ecological and evolutionary processes shaping adaptive population structure.

genomics↗

bioRxiv2019

Riverscape genetics in brook lamprey: genetic diversity is less influenced by river fragmentation than by gene flow with the anadromous ecotype

Understanding the effect of human induced landscape fragmentation on gene flow and evolutionary potential of wild populations has become a major concern. Here, we investigated the effect of riverscape fragmentation on patterns of genetic diversity in the freshwater resident brook lamprey (Lampetra planeri) that has a low ability to pass obstacles to migration. We also tested the hypotheses of i) asymmetric gene flow following water current and ii) admixture with the closely related anadromous L. fluviatilis ecotype having a positive effect on L. planeri genetic diversity. We genotyped 2472 individuals, including 225 L. fluviatilis, sampled in 81 sites upstream and downstream from barriers to migration, in 29 West-European rivers. Linear modelling revealed a strong positive relationship between the distance to the source and genetic diversity, consistent with expected patterns of decreased gene flow into upstream populations. However, the presence of anthropogenic barriers had a moderate effect on spatial genetic structure. Accordingly, we found evidence for downstream-directed gene flow, supporting the hypothesis that barriers do not limit dispersal following water flow. Downstream L. planeri populations in sympatry with L. fluviatilis displayed consistently higher genetic diversity. We conclude that genetic drift and slight downstream gene flow mainly drive the genetic make up of upstream L. planeri populations whereas admixture between ecotypes maintains higher levels of genetic diversity in L. planeri populations sympatric with L. fluviatilis. We discuss the implications of these results for the design of conservation strategies of lamprey, and other freshwater organisms with several ecotypes, in fragmented dendritic river networks.

evolutionary biology↗

bioRxiv2019

Genomics of local adaptation in blue tit

Understanding the genomic processes underlying local adaptation is a central aim of modern evolutionary biology. This task requires identifying footprints of local selection but also estimating spatio-temporal variation in population demography and variation in recombination rate and diversity along the genome. Here, we investigated these parameters in blue tit populations inhabiting deciduous versus evergreen forests and insular versus mainland areas, in the context of a previously described strong phenotypic differentiation. Neighboring population pairs of deciduous and evergreen habitats were weakly genetically differentiated (FST = 0.004 on average), nevertheless with a statistically significant effect of habitat type on the overall genetic structure. This low differentiation was consistent with the strong and long-lasting gene flow between populations, inferred by demographic modeling. In turn, insular and mainland populations were moderately differentiated (FST = 0.08 on average), in line with the inference of moderate ancestral migrations, followed by isolation since the end of the last glaciation. Effective population sizes were overall large, yet smaller on the island than on the mainland. Weak and non-parallel footprints of divergent selection between deciduous and evergreen populations were consistent with their high connectivity and the probable polygenic nature of local adaptation in these habitats. In turn, stronger footprints of divergent selection were identified between long isolated insular versus mainland birds, and were more often found in regions of low recombination as expected from theory. Lastly, we identified a genomic inversion on the mainland, spanning 2.8Mb. These results provide insights into the demographic history and genetic architecture of local adaptation in blue tit populations at multiple geographic scales.

evolutionary biology↗

bioRxiv2019

Standing genetic variation and chromosomal rearrangements facilitate local adaptation in a marine fish

Population genetic theory states that adaptation most frequently occurs from standing genetic variation, which results from the interplay between different evolutionary processes including mutation, chromosomal rearrangements, drift, gene flow and selection. To date, empirical work focusing on the contribution of standing genetic variation to local adaptation in the presence of high gene flow has been limited to a restricted number of study systems. Marine organisms are excellent biological models to address this issue since many species have to cope with variable environmental conditions acting as selective agents despite high dispersal abilities. In this study, we examined how, demographic history, standing genetic variation linked to chromosomal rearrangements and shared polymorphism among glacial lineages contribute to local adaptation to environmental conditions in the marine fish, the capelin (Mallotus villosus). We used a comprehensive dataset of genome-wide single nucleotide polymorphisms (25,904 filtered SNPs) genotyped in 1,359 individuals collected from 31 spawning sites in the northwest Atlantic (North America and Greenland waters). First, we reconstructed the history of divergence among three glacial lineages and showed that they diverged from 3.8 to 1.8 MyA. Depending on the pair of lineages considered, historical demographic modelling provided evidence for divergence with gene flow and secondary contacts, shaped by barriers to gene flow and linked selection. We next identified candidate loci associated with reproductive isolation of these lineages. Given the absence of physical or geographic barriers, we thus propose that these lineages may represent three cryptic species of capelin. Within each of these, our analyses provided evidence for large Ne and high gene flow at both historical and contemporary time scales among spawning sites. Furthermore, we detected a polymorphic chromosomal rearrangement leading to the coexistence of three haplogroups within the Northwest Atlantic lineage, but absent in the other two clades. Genotype-environment associations revealed molecular signatures of local adaptation to environmental conditions prevailing at spawning sites. Altogether, our study shows that standing genetic variation associated with both chromosomal rearrangements and ancestral polymorphism contribute to local adaptation in the presence of high gene flow.

genomics↗

bioRxiv2019

Demographic history, linked selection, and recombination shape the genomic landscape of a broadly distributed Pacific salmon.

A thorough reconstruction of historical processes is essential for a comprehensive understanding the mechanisms shaping patterns of genetic diversity. Indeed, past and current conditions influencing effective population size have important evolutionary implications for the efficacy of selection, increased accumulation of deleterious mutations, and loss of adaptive potential. Here, we gather extensive genome-wide data that represent the extant diversity of the Coho salmon (Oncorhynchus kisutch) to address two objectives. We demonstrate that a single glacial refugium is the source of most of the present-day genetic diversity, with detectable inputs from a putative secondary micro-refugium. We found statistical support for a scenario whereby ancestral populations located south of the ice sheets expanded in postglacial time, swamping out most of the diversity from other putative micro-refugia. Demographic inferences revealed that genetic diversity was also affected by linked selection in large parts of the genome. Moreover, we demonstrate that the recent demographic history of this species generated regional differences in the load of deleterious mutations among populations, a finding that mirrors recent results from human populations and provides increased support for models of expansion load. We propose that insights from these historical inferences should be better integrated in conservation planning of wild organisms, which currently focuses largely on neutral genetic diversity and local adaptation, with the role of potentially maladaptive variation being generally ignored.

evolutionary biology↗

bioRxiv2018

Combining population genomics and forward simulations to investigate stocking impacts: A case study of Muskellunge (Esox masquinongy) from the St. Lawrence River basin

Understanding the genetic and evolutionary impacts of fish stocking on wild populations has long been of interest as negative consequences such as reduced fitness and loss of genetic resources are commonly reported. Nearly five decades of extensive stocking of over a million Muskellunge (Esox masquinongy) in the Lower St. Lawrence River (Quebec, Canada) was implemented by managers in an attempt to sustain a fishery. We investigated the effect of stocking on this native species genetic structure and allelic diversity in the St. Lawrence river and its tributaries as well as several stocked inland lakes. Using Genotype-By-Sequencing (GBS), we genotyped 643 individuals representing 22 sampling sites and combined this information with forward simulations to investigate the genetic consequences of stocking. Individuals native to the St. Lawrence watershed were genetically divergent from the sources used for stocking and both the St. Lawrence tributaries and inland lakes were also naturally divergent from the main stem. Empirical data and simulations revealed weak effects of stocking on admixture patterns within the St. Lawrence despite intense stocking in the past, whereas footprints of admixture were higher in the smaller stocked populations from tributaries and lakes. Altogether, our data suggests that selection against introgression has been relatively efficient within the large St. Lawrence River. In contrast, the smaller populations from adjacent tributaries and lakes still displayed stocking related admixture which apparently resulted in higher genetic diversity, suggesting that, while stocking stopped at the same time, its impact remained higher in these populations. Finally, the origin of populations from inland lakes that were established by stocking confirmed their close affinity with these source populations. This study illustrates the benefit of combining extensive genomic data with forward simulations for improved inferences regarding outcomes of population enhancement by stocking, as well as its relevance for fishery management decision making.

evolutionary biology↗

bioRxiv2018

Secondary contacts between European white oaks reveal genes underlying reproductive isolation

AO_SCPLOWBSTRACTC_SCPLOWOaks are dominant forest tree species widely distributed across the Northern Hemisphere, where they constitute natural resources of economic, ecological, social and historical value. Hybridization and adaptive introgression have long been thought to be major drivers of their ecological success. Thus, the maintenance of species barriers remains a key question, given the extent of interspecific gene flow. In this study, we scanned the genomes of four European white oak species for reproductive barriers. We identified the ecological and phylogenic relationships of these species and inferred a long-term strict isolation followed by a recent and extensive postglacial contact. Then, we made use of the tremendous genetic variation among these species (31 million SNPs) to identify genomic regions for reproductive isolation. A literature-based functional annotation of the underlying genes highlighted important functions driving the reproductive isolation between these sister species. These functions were consistent with their ecological preferences and included tolerance to biotic and abiotic constraints. This study holds important implications for the renewal of European forests under global warming.

evolutionary biology↗

bioRxiv2017

Reconstructing The Demographic History Of Atlantic Salmon (Salmo salar) Across Its Distribution Range Using Approximate Bayesian Computations

Understanding the dual roles of demographic and selective processes in the buildup of population divergence is one of the most challenging tasks in evolutionary biology. In the Northern hemisphere in particular, species genetic makeup has been largely influenced by severe climatic oscillations of the Quaternary Period. Here, we investigated the demographic history of Atlantic Salmon across the entire species range using 2035 anadromous individuals from 77 sampling sites from North America and Eurasia genotyped at 4,656 SNPs. By combining results from admixture graphs, geogenetic maps and an approximate Bayesian computation framework, we validate previous hypotheses pertaining to secondary contact between European and Northern American populations, but also demonstrate that European populations from different glacial refugia have been exchanging alleles in contemporary times. We further identify the major sources of admixture from the southern range of North America to more northern populations along with a strong signal of secondary gene flow between genetic regional groups. We hypothesize that these patterns reflects the spatial redistribution of ancestral variation across the entire American range. Results also point to a role for linked selection in the form of background selection and or positive hitchhiking. Altogether, differential introgression and linked selective effects likely played an underappreciated role in shaping the genomic landscape of species in the Northern hemisphere Therefore we conclude that such heterogeneity among loci should be systematically integrated into demographic inferences of the divergence process, even between incompletely reproductively isolated populations.

evolutionary biology↗