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Pfennig A, Lachance J. The evolutionary fate of Neanderthal DNA in 30,780 admixed genomes with recent African-like ancestry. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.07.25.605203. [PMID: 39091830 PMCID: PMC11291122 DOI: 10.1101/2024.07.25.605203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 08/04/2024]
Abstract
Following introgression, Neanderthal DNA was initially purged from non-African genomes, but the evolutionary fate of remaining introgressed DNA has not been explored yet. To fill this gap, we analyzed 30,780 admixed genomes with African-like ancestry from the All of Us research program, in which Neanderthal alleles encountered novel genetic backgrounds during the last 15 generations. Observed amounts of Neanderthal DNA approximately match expectations based on ancestry proportions, suggesting neutral evolution. Nevertheless, we identified genomic regions that have significantly less or more Neanderthal ancestry than expected and are associated with spermatogenesis, innate immunity, and other biological processes. We also identified three novel introgression desert-like regions in recently admixed genomes, whose genetic features are compatible with hybrid incompatibilities and intrinsic negative selection. Overall, we find that much of the remaining Neanderthal DNA in human genomes is not under strong selection, and complex evolutionary dynamics have shaped introgression landscapes in our species.
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Affiliation(s)
- Aaron Pfennig
- School of Biological Sciences, Georgia Institute of Technology, 950 Atlantic Dr, Atlanta, 30332, GA, USA
| | - Joseph Lachance
- School of Biological Sciences, Georgia Institute of Technology, 950 Atlantic Dr, Atlanta, 30332, GA, USA
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2
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McFarlane SE, Jahner JP, Lindtke D, Buerkle CA, Mandeville EG. Selection leads to remarkable variability in the outcomes of hybridisation across replicate hybrid zones. Mol Ecol 2024; 33:e17359. [PMID: 38699787 DOI: 10.1111/mec.17359] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2022] [Revised: 04/03/2024] [Accepted: 04/05/2024] [Indexed: 05/05/2024]
Abstract
Hybrid zones have been viewed as an opportunity to see speciation in action. When hybrid zones are replicated, it is assumed that if the same genetic incompatibilities are maintaining reproductive isolation across all instances of secondary contact, those incompatibilities should be identifiable by consistent patterns in the genome. In contrast, changes in allele frequencies due to genetic drift should be idiosyncratic for each hybrid zone. To test this assumption, we simulated 20 replicates of each of 12 hybrid zone scenarios with varied genetic incompatibilities, rates of migration, selection and different starting population size ratios of parental species. We found remarkable variability in the outcomes of hybridisation in replicate hybrid zones, particularly with Bateson-Dobzhansky-Muller incompatibilities and strong selection. We found substantial differences among replicates in the overall genomic composition of individuals, including admixture proportions, inter-specific ancestry complement and number of ancestry junctions. Additionally, we found substantial variation in genomic clines among replicates at focal loci, regardless of locus-specific selection. We conclude that processes other than selection are responsible for some consistent outcomes of hybridisation, whereas selection on incompatibilities can lead to genomically widespread and highly variable outcomes. We highlight the challenge of mapping between pattern and process in hybrid zones and call attention to how selection against incompatibilities will commonly lead to variable outcomes. We hope that this study informs future research on replicate hybrid zones and encourages further development of statistical techniques, theoretical models and exploration of additional axes of variation to understand reproductive isolation.
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Affiliation(s)
- S Eryn McFarlane
- Department of Botany, University of Wyoming, Laramie, Wyoming, USA
- Department of Biology, York University, Toronto, Ontario, Canada
| | - Joshua P Jahner
- Department of Botany, University of Wyoming, Laramie, Wyoming, USA
| | | | - C Alex Buerkle
- Department of Botany, University of Wyoming, Laramie, Wyoming, USA
| | - Elizabeth G Mandeville
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada
- Biology Department, Northern Michigan University, Marquette, Michigan, USA
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3
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Dagilis AJ, Matute DR. The fitness of an introgressing haplotype changes over the course of divergence and depends on its size and genomic location. PLoS Biol 2023; 21:e3002185. [PMID: 37459351 PMCID: PMC10374083 DOI: 10.1371/journal.pbio.3002185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2023] [Revised: 07/27/2023] [Accepted: 06/06/2023] [Indexed: 07/28/2023] Open
Abstract
The genomic era has made clear that introgression, or the movement of genetic material between species, is a common feature of evolution. Examples of both adaptive and deleterious introgression exist in a variety of systems. What is unclear is how the fitness of an introgressing haplotype changes as species diverge or as the size of the introgressing haplotype changes. In a simple model, we show that introgression may more easily occur into parts of the genome which have not diverged heavily from a common ancestor. The key insight is that alleles from a shared genetic background are likely to have positive epistatic interactions, increasing the fitness of a larger introgressing block. In regions of the genome where few existing substitutions are disrupted, this positive epistasis can be larger than incompatibilities with the recipient genome. Further, we show that early in the process of divergence, introgression of large haplotypes can be favored more than introgression of individual alleles. This model is consistent with observations of a positive relationship between recombination rate and introgression frequency across the genome; however, it generates several novel predictions. First, the model suggests that the relationship between recombination rate and introgression may not exist, or may be negative, in recently diverged species pairs. Furthermore, the model suggests that introgression that replaces existing derived variation will be more deleterious than introgression at sites carrying ancestral variants. These predictions are tested in an example of introgression in Drosophila melanogaster, with some support for both. Finally, the model provides a potential alternative explanation to asymmetry in the direction of introgression, with expectations of higher introgression from rapidly diverged populations into slowly evolving ones.
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Affiliation(s)
- Andrius J Dagilis
- Biology Department, University of North Carolina, Chapel Hill, North Carolina, United States of America
| | - Daniel R Matute
- Biology Department, University of North Carolina, Chapel Hill, North Carolina, United States of America
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4
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Huang J, Thawornwattana Y, Flouri T, Mallet J, Yang Z. Inference of Gene Flow between Species under Misspecified Models. Mol Biol Evol 2022; 39:6783212. [PMID: 36317198 PMCID: PMC9729068 DOI: 10.1093/molbev/msac237] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
Genomic sequence data provide a rich source of information about the history of species divergence and interspecific hybridization or introgression. Despite recent advances in genomics and statistical methods, it remains challenging to infer gene flow, and as a result, one may have to estimate introgression rates and times under misspecified models. Here we use mathematical analysis and computer simulation to examine estimation bias and issues of interpretation when the model of gene flow is misspecified in analysis of genomic datasets, for example, if introgression is assigned to the wrong lineages. In the case of two species, we establish a correspondence between the migration rate in the continuous migration model and the introgression probability in the introgression model. When gene flow occurs continuously through time but in the analysis is assumed to occur at a fixed time point, common evolutionary parameters such as species divergence times are surprisingly well estimated. However, the time of introgression tends to be estimated towards the recent end of the period of continuous gene flow. When introgression events are assigned incorrectly to the parental or daughter lineages, introgression times tend to collapse onto species divergence times, with introgression probabilities underestimated. Overall, our analyses suggest that the simple introgression model is useful for extracting information concerning between-specific gene flow and divergence even when the model may be misspecified. However, for reliable inference of gene flow it is important to include multiple samples per species, in particular, from hybridizing species.
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Affiliation(s)
| | | | - Tomáš Flouri
- Department of Genetics, Evolution and Environment, University College London, London WC1E 6BT, United Kingdom
| | - James Mallet
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138
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5
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Pfennig A, Lachance J. Hybrid fitness effects modify fixation probabilities of introgressed alleles. G3 GENES|GENOMES|GENETICS 2022; 12:6583188. [PMID: 35536195 PMCID: PMC9258535 DOI: 10.1093/g3journal/jkac113] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/04/2021] [Accepted: 04/28/2022] [Indexed: 11/12/2022]
Abstract
Hybridization is a common occurrence in natural populations, and introgression is a major source of genetic variation. Despite the evolutionary importance of adaptive introgression, classical population genetics theory does not take into account hybrid fitness effects. Specifically, heterosis (i.e. hybrid vigor) and Dobzhansky–Muller incompatibilities influence the fates of introgressed alleles. Here, we explicitly account for polygenic, unlinked hybrid fitness effects when tracking a rare introgressed marker allele. These hybrid fitness effects quickly decay over time due to repeated backcrossing, enabling a separation-of-timescales approach. Using diffusion and branching process theory in combination with computer simulations, we formalize the intuition behind how hybrid fitness effects affect introgressed alleles. We find that hybrid fitness effects can significantly hinder or boost the fixation probability of introgressed alleles, depending on the relative strength of heterosis and Dobzhansky–Muller incompatibilities effects. We show that the inclusion of a correction factor (α, representing the compounded effects of hybrid fitness effects over time) into classic population genetics theory yields accurate fixation probabilities. Despite having a strong impact on the probability of fixation, hybrid fitness effects only subtly change the distribution of fitness effects of introgressed alleles that reach fixation. Although strong Dobzhansky–Muller incompatibility effects may expedite the loss of introgressed alleles, fixation times are largely unchanged by hybrid fitness effects.
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Affiliation(s)
- Aaron Pfennig
- School of Biological Sciences, Georgia Institute of Technology , Atlanta, GA 30332, USA
| | - Joseph Lachance
- School of Biological Sciences, Georgia Institute of Technology , Atlanta, GA 30332, USA
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6
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Nürnberger B, Baird SJE, Čížková D, Bryjová A, Mudd AB, Blaxter ML, Szymura JM. A dense linkage map for a large repetitive genome: discovery of the sex-determining region in hybridizing fire-bellied toads (Bombina bombina and Bombina variegata). G3 (BETHESDA, MD.) 2021; 11:6353606. [PMID: 34849761 PMCID: PMC8664441 DOI: 10.1093/g3journal/jkab286] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Accepted: 08/16/2021] [Indexed: 12/20/2022]
Abstract
Genomic analysis of hybrid zones offers unique insights into emerging reproductive isolation and the dynamics of introgression. Because hybrid genomes consist of blocks inherited from one or the other parental taxon, linkage information is essential. In most cases, the spectrum of local ancestry tracts can be efficiently uncovered from dense linkage maps. Here, we report the development of such a map for the hybridizing toads, Bombina bombina and Bombina variegata (Anura: Bombinatoridae). Faced with the challenge of a large (7–10 Gb), repetitive genome, we set out to identify a large number of Mendelian markers in the nonrepetitive portion of the genome that report B. bombina vs B. variegata ancestry with appropriately quantified statistical support. Bait sequences for targeted enrichment were selected from a draft genome assembly, after filtering highly repetitive sequences. We developed a novel approach to infer the most likely diplotype per sample and locus from the raw read mapping data, which is robust to over-merging and obviates arbitrary filtering thresholds. Validation of the resulting map with 4755 markers underscored the large-scale synteny between Bombina and Xenopus tropicalis. By assessing the sex of late-stage F2 tadpoles from histological sections, we identified the sex-determining region in the Bombina genome to 7 cM on LG5, which is homologous to X. tropicalis chromosome 5, and inferred male heterogamety. Interestingly, chromosome 5 has been repeatedly recruited as a sex chromosome in anurans with XY sex determination.
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Affiliation(s)
- Beate Nürnberger
- Research Facility Studenec, Institute of Vertebrate Biology, Czech Academy of Sciences, 603 65 Brno, Czech Republic
| | - Stuart J E Baird
- Research Facility Studenec, Institute of Vertebrate Biology, Czech Academy of Sciences, 603 65 Brno, Czech Republic
| | - Dagmar Čížková
- Research Facility Studenec, Institute of Vertebrate Biology, Czech Academy of Sciences, 603 65 Brno, Czech Republic
| | - Anna Bryjová
- Research Facility Studenec, Institute of Vertebrate Biology, Czech Academy of Sciences, 603 65 Brno, Czech Republic
| | - Austin B Mudd
- Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, 94720 CA, USA
| | - Mark L Blaxter
- Tree of Life Programme, Wellcome Sanger Institute, Hinxton, Cambridge CB10 1SA, UK
| | - Jacek M Szymura
- Department of Comparative Anatomy, Jagiellonian University, 30-387 Kraków, Poland
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7
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Moran BM, Payne C, Langdon Q, Powell DL, Brandvain Y, Schumer M. The genomic consequences of hybridization. eLife 2021; 10:e69016. [PMID: 34346866 PMCID: PMC8337078 DOI: 10.7554/elife.69016] [Citation(s) in RCA: 94] [Impact Index Per Article: 31.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Accepted: 07/09/2021] [Indexed: 12/29/2022] Open
Abstract
In the past decade, advances in genome sequencing have allowed researchers to uncover the history of hybridization in diverse groups of species, including our own. Although the field has made impressive progress in documenting the extent of natural hybridization, both historical and recent, there are still many unanswered questions about its genetic and evolutionary consequences. Recent work has suggested that the outcomes of hybridization in the genome may be in part predictable, but many open questions about the nature of selection on hybrids and the biological variables that shape such selection have hampered progress in this area. We synthesize what is known about the mechanisms that drive changes in ancestry in the genome after hybridization, highlight major unresolved questions, and discuss their implications for the predictability of genome evolution after hybridization.
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Affiliation(s)
- Benjamin M Moran
- Department of Biology, Stanford UniversityStanfordUnited States
- Centro de Investigaciones Científicas de las Huastecas “Aguazarca”HidalgoMexico
| | - Cheyenne Payne
- Department of Biology, Stanford UniversityStanfordUnited States
- Centro de Investigaciones Científicas de las Huastecas “Aguazarca”HidalgoMexico
| | - Quinn Langdon
- Department of Biology, Stanford UniversityStanfordUnited States
| | - Daniel L Powell
- Department of Biology, Stanford UniversityStanfordUnited States
- Centro de Investigaciones Científicas de las Huastecas “Aguazarca”HidalgoMexico
| | - Yaniv Brandvain
- Department of Ecology, Evolution & Behavior and Plant and Microbial Biology, University of MinnesotaMinneapolisUnited States
| | - Molly Schumer
- Department of Biology, Stanford UniversityStanfordUnited States
- Centro de Investigaciones Científicas de las Huastecas “Aguazarca”HidalgoMexico
- Hanna H. Gray Fellow, Howard Hughes Medical InstituteStanfordUnited States
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8
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Yair S, Lee KM, Coop G. The timing of human adaptation from Neanderthal introgression. Genetics 2021; 218:iyab052. [PMID: 33787889 PMCID: PMC8128397 DOI: 10.1093/genetics/iyab052] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Accepted: 02/26/2021] [Indexed: 12/26/2022] Open
Abstract
Admixture has the potential to facilitate adaptation by providing alleles that are immediately adaptive in a new environment or by simply increasing the long-term reservoir of genetic diversity for future adaptation. A growing number of cases of adaptive introgression are being identified in species across the tree of life, however the timing of selection, and therefore the importance of the different evolutionary roles of admixture, is typically unknown. Here, we investigate the spatio-temporal history of selection favoring Neanderthal-introgressed alleles in modern human populations. Using both ancient and present-day samples of modern humans, we integrate the known demographic history of populations, namely population divergence and migration, with tests for selection. We model how a sweep placed along different branches of an admixture graph acts to modify the variance and covariance in neutral allele frequencies among populations at linked loci. Using a method based on this model of allele frequencies, we study previously identified cases of adaptive Neanderthal introgression. From these, we identify cases in which Neanderthal-introgressed alleles were quickly beneficial and other cases in which they persisted at low frequency for some time. For some of the alleles that persisted at low frequency, we show that selection likely independently favored them later on in geographically separated populations. Our work highlights how admixture with ancient hominins has contributed to modern human adaptation and contextualizes observed levels of Neanderthal ancestry in present-day and ancient samples.
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Affiliation(s)
- Sivan Yair
- Center for Population Biology, University of California, Davis, Davis, CA 95616, USA
- Department of Evolution and Ecology, University of California, Davis, Davis, CA 95616, USA
| | - Kristin M Lee
- Department of Biological Sciences, Columbia University, New York, NY 10027, USA
| | - Graham Coop
- Center for Population Biology, University of California, Davis, Davis, CA 95616, USA
- Department of Evolution and Ecology, University of California, Davis, Davis, CA 95616, USA
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9
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Bisschop G, Setter D, Rafajlović M, Baird SJE, Lohse K. The impact of global selection on local adaptation and reproductive isolation. Philos Trans R Soc Lond B Biol Sci 2020; 375:20190531. [PMID: 32654652 PMCID: PMC7423272 DOI: 10.1098/rstb.2019.0531] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Despite the homogenizing effect of strong gene flow between two populations, adaptation under symmetric divergent selection pressures results in partial reproductive isolation: adaptive substitutions act as local barriers to gene flow, and if divergent selection continues unimpeded, this will result in complete reproductive isolation of the two populations, i.e. speciation. However, a key issue in framing the process of speciation as a tension between local adaptation and the homogenizing force of gene flow is that the mutation process is blind to changes in the environment and therefore tends to limit adaptation. Here we investigate how globally beneficial mutations (GBMs) affect divergent local adaptation and reproductive isolation. When phenotypic divergence is finite, we show that the presence of GBMs limits local adaptation, generating a persistent genetic load at the loci that contribute to the trait under divergent selection and reducing genome-wide divergence. Furthermore, we show that while GBMs cannot prohibit the process of continuous differentiation, they induce a substantial delay in the genome-wide shutdown of gene flow. This article is part of the theme issue ‘Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers’.
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Affiliation(s)
- Gertjan Bisschop
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, UK
| | - Derek Setter
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, UK
| | - Marina Rafajlović
- Department of Marine Sciences, Centre for Marine Evolutionary Biology, University of Gothenburg, Gothenburg, Sweden
| | - Stuart J E Baird
- Institute of Vertebrate Biology, Academy of Sciences of the Czech Republic, Brno, Czech Republic
| | - Konrad Lohse
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, UK
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10
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Shang H, Hess J, Pickup M, Field DL, Ingvarsson PK, Liu J, Lexer C. Evolution of strong reproductive isolation in plants: broad-scale patterns and lessons from a perennial model group. Philos Trans R Soc Lond B Biol Sci 2020; 375:20190544. [PMID: 32654641 DOI: 10.1098/rstb.2019.0544] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Many recent studies have addressed the mechanisms operating during the early stages of speciation, but surprisingly few studies have tested theoretical predictions on the evolution of strong reproductive isolation (RI). To help address this gap, we first undertook a quantitative review of the hybrid zone literature for flowering plants in relation to reproductive barriers. Then, using Populus as an exemplary model group, we analysed genome-wide variation for phylogenetic tree topologies in both early- and late-stage speciation taxa to determine how these patterns may be related to the genomic architecture of RI. Our plant literature survey revealed variation in barrier complexity and an association between barrier number and introgressive gene flow. Focusing on Populus, our genome-wide analysis of tree topologies in speciating poplar taxa points to unusually complex genomic architectures of RI, consistent with earlier genome-wide association studies. These architectures appear to facilitate the 'escape' of introgressed genome segments from polygenic barriers even with strong RI, thus affecting their relationships with recombination rates. Placed within the context of the broader literature, our data illustrate how phylogenomic approaches hold great promise for addressing the evolution and temporary breakdown of RI during late stages of speciation. This article is part of the theme issue 'Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers'.
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Affiliation(s)
- Huiying Shang
- Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, 1030 Vienna, Austria.,Vienna Graduate School of Population Genetics, Vienna, Austria
| | - Jaqueline Hess
- Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, 1030 Vienna, Austria.,Helmholtz Centre for Environmental Research, Halle (Saale), Germany
| | - Melinda Pickup
- Institute of Science and Technology (IST), Klosterneuburg, Austria
| | - David L Field
- Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, 1030 Vienna, Austria.,Edith Cowan University, Perth, Australia
| | - Pär K Ingvarsson
- Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden
| | - Jianquan Liu
- Key Laboratory for Bio-resources and Eco-environment, College of Life Science, Sichuan University, Chengdu, People's Republic of China
| | - Christian Lexer
- Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, 1030 Vienna, Austria
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11
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VolcanoFinder: Genomic scans for adaptive introgression. PLoS Genet 2020; 16:e1008867. [PMID: 32555579 PMCID: PMC7326285 DOI: 10.1371/journal.pgen.1008867] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Revised: 06/30/2020] [Accepted: 05/18/2020] [Indexed: 12/16/2022] Open
Abstract
Recent research shows that introgression between closely-related species is an important source of adaptive alleles for a wide range of taxa. Typically, detection of adaptive introgression from genomic data relies on comparative analyses that require sequence data from both the recipient and the donor species. However, in many cases, the donor is unknown or the data is not currently available. Here, we introduce a genome-scan method—VolcanoFinder—to detect recent events of adaptive introgression using polymorphism data from the recipient species only. VolcanoFinder detects adaptive introgression sweeps from the pattern of excess intermediate-frequency polymorphism they produce in the flanking region of the genome, a pattern which appears as a volcano-shape in pairwise genetic diversity. Using coalescent theory, we derive analytical predictions for these patterns. Based on these results, we develop a composite-likelihood test to detect signatures of adaptive introgression relative to the genomic background. Simulation results show that VolcanoFinder has high statistical power to detect these signatures, even for older sweeps and for soft sweeps initiated by multiple migrant haplotypes. Finally, we implement VolcanoFinder to detect archaic introgression in European and sub-Saharan African human populations, and uncovered interesting candidates in both populations, such as TSHR in Europeans and TCHH-RPTN in Africans. We discuss their biological implications and provide guidelines for identifying and circumventing artifactual signals during empirical applications of VolcanoFinder. The process by which beneficial alleles are introduced into a species from a closely-related species is termed adaptive introgression. We present an analytically-tractable model for the effects of adaptive introgression on non-adaptive genetic variation in the genomic region surrounding the beneficial allele. The result we describe is a characteristic volcano-shaped pattern of increased variability that arises around the positively-selected site, and we introduce an open-source method VolcanoFinder to detect this signal in genomic data. Importantly, VolcanoFinder is a population-genetic likelihood-based approach, rather than a comparative-genomic approach, and can therefore probe genomic variation data from a single population for footprints of adaptive introgression, even from a priori unknown and possibly extinct donor species.
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12
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Abstract
Interspecific hybridization is the process where closely related species mate and produce offspring with admixed genomes. The genomic revolution has shown that hybridization is common, and that it may represent an important source of novel variation. Although most interspecific hybrids are sterile or less fit than their parents, some may survive and reproduce, enabling the transfer of adaptive variants across the species boundary, and even result in the formation of novel evolutionary lineages. There are two main variants of hybrid species genomes: allopolyploid, which have one full chromosome set from each parent species, and homoploid, which are a mosaic of the parent species genomes with no increase in chromosome number. The establishment of hybrid species requires the development of reproductive isolation against parental species. Allopolyploid species often have strong intrinsic reproductive barriers due to differences in chromosome number, and homoploid hybrids can become reproductively isolated from the parent species through assortment of genetic incompatibilities. However, both types of hybrids can become further reproductively isolated, gaining extrinsic isolation barriers, by exploiting novel ecological niches, relative to their parents. Hybrids represent the merging of divergent genomes and thus face problems arising from incompatible combinations of genes. Thus hybrid genomes are highly dynamic and undergo rapid evolutionary change, including genome stabilization in which selection against incompatible combinations results in fixation of compatible ancestry block combinations within the hybrid species. The potential for rapid adaptation or speciation makes hybrid genomes a particularly exciting subject of in evolutionary biology. Here we summarize how introgressed alleles or hybrid species can establish and how the resulting hybrid genomes evolve.
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Affiliation(s)
- Anna Runemark
- Department of Biology, Lund University, Lund, Sweden
- * E-mail:
| | - Mario Vallejo-Marin
- Biological and Environmental Sciences, University of Stirling, Stirling, Scotland, United Kingdom
| | - Joana I. Meier
- St John's College, Cambridge, Cambridge, United Kingdom
- Department of Zoology, University of Cambridge, Cambridge, United Kingdom
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13
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Marques DA, Meier JI, Seehausen O. A Combinatorial View on Speciation and Adaptive Radiation. Trends Ecol Evol 2019; 34:531-544. [DOI: 10.1016/j.tree.2019.02.008] [Citation(s) in RCA: 162] [Impact Index Per Article: 32.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Revised: 02/07/2019] [Accepted: 02/13/2019] [Indexed: 01/28/2023]
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14
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Oziolor EM, Reid NM, Yair S, Lee KM, Guberman VerPloeg S, Bruns PC, Shaw JR, Whitehead A, Matson CW. Adaptive introgression enables evolutionary rescue from extreme environmental pollution. Science 2019; 364:455-457. [DOI: 10.1126/science.aav4155] [Citation(s) in RCA: 114] [Impact Index Per Article: 22.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2018] [Accepted: 03/25/2019] [Indexed: 12/19/2022]
Abstract
Radical environmental change that provokes population decline can impose constraints on the sources of genetic variation that may enable evolutionary rescue. Adaptive toxicant resistance has rapidly evolved in Gulf killifish (Fundulus grandis) that occupy polluted habitats. We show that resistance scales with pollution level and negatively correlates with inducibility of aryl hydrocarbon receptor (AHR) signaling. Loci with the strongest signatures of recent selection harbor genes regulating AHR signaling. Two of these loci introgressed recently (18 to 34 generations ago) from Atlantic killifish (F. heteroclitus). One introgressed locus contains a deletion in AHR that confers a large adaptive advantage [selection coefficient (s) = 0.8]. Given the limited migration of killifish, recent adaptive introgression was likely mediated by human-assisted transport. We suggest that interspecies connectivity may be an important source of adaptive variation during extreme environmental change.
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15
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Replicability of Introgression Under Linked, Polygenic Selection. Genetics 2018; 210:1411-1427. [PMID: 30274989 DOI: 10.1534/genetics.118.301429] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2018] [Accepted: 09/28/2018] [Indexed: 11/18/2022] Open
Abstract
We study how a block of genome with a large number of weakly selected loci introgresses under directional selection into a genetically homogeneous population. We derive exact expressions for the expected rate of growth of any fragment of the introduced block during the initial phase of introgression, and show that the growth rate of a single-locus variant is largely insensitive to its own additive effect, but depends instead on the combined effect of all loci within a characteristic linkage scale. The expected growth rate of a fragment is highly correlated with its long-term introgression probability in populations of moderate size, and can hence identify variants that are likely to introgress across replicate populations. We clarify how the introgression probability of an individual variant is determined by the interplay between hitchhiking with relatively large fragments during the early phase of introgression and selection on fine-scale variation within these, which at longer times results in differential introgression probabilities for beneficial and deleterious loci within successful fragments. By simulating individuals, we also investigate how introgression probabilities at individual loci depend on the variance of fitness effects, the net fitness of the introduced block, and the size of the recipient population, and how this shapes the net advance under selection. Our work suggests that even highly replicable substitutions may be associated with a range of selective effects, which makes it challenging to fine map the causal loci that underlie polygenic adaptation.
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Introgression of a Block of Genome Under Infinitesimal Selection. Genetics 2018; 209:1279-1303. [PMID: 29895560 DOI: 10.1534/genetics.118.301018] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2018] [Accepted: 05/25/2018] [Indexed: 11/18/2022] Open
Abstract
Adaptive introgression is common in nature and can be driven by selection acting on multiple, linked genes. We explore the effects of polygenic selection on introgression under the infinitesimal model with linkage. This model assumes that the introgressing block has an effectively infinite number of loci, each with an infinitesimal effect on the trait under selection. The block is assumed to introgress under directional selection within a native population that is genetically homogeneous. We use individual-based simulations and a branching process framework to compute various statistics of the introgressing block, and explore how these depend on parameters such as the map length and initial trait value associated with the introgressing block, the genetic variability along the block, and the strength of selection. Our results show that the introgression dynamics of a block under infinitesimal selection are qualitatively different from the dynamics of neutral introgression. We also find that, in the long run, surviving descendant blocks are likely to have intermediate lengths, and clarify how their length is shaped by the interplay between linkage and infinitesimal selection. Our results suggest that it may be difficult to distinguish the long-term introgression of a block of genome with a single, strongly selected, locus from the introgression of a block with multiple, tightly linked and weakly selected loci.
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Dannemann M, Racimo F. Something old, something borrowed: admixture and adaptation in human evolution. Curr Opin Genet Dev 2018; 53:1-8. [PMID: 29894925 DOI: 10.1016/j.gde.2018.05.009] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2018] [Revised: 05/21/2018] [Accepted: 05/24/2018] [Indexed: 01/09/2023]
Abstract
The sequencing of ancient DNA from archaic humans-Neanderthals and Denisovans-has revealed that modern and archaic humans interbred at least twice during the Pleistocene. The field of human paleogenomics has now turned its attention towards understanding the nature of this genetic legacy in the gene pool of present-day humans. What exactly did modern humans obtain from interbreeding with Neanderthals and Denisovans? Was the introgressed genetic material beneficial, neutral or maladaptive? Can differences in phenotypes among present-day human populations be explained by archaic human introgression? These questions are of prime importance for our understanding of recent human evolution, but will require careful computational modeling and extensive functional assays before they can be answered in full. Here, we review the recent literature characterizing introgressed DNA and the likely biological consequences for their modern human carriers. We focus particularly on archaic human haplotypes that were beneficial to modern humans as they expanded across the globe, and on ways to understand how populations harboring these haplotypes evolved over time.
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Affiliation(s)
- Michael Dannemann
- Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
| | - Fernando Racimo
- Centre for GeoGenetics, Natural History Museum of Denmark, Copenhagen, Denmark.
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Turissini DA, Matute DR. Fine scale mapping of genomic introgressions within the Drosophila yakuba clade. PLoS Genet 2017; 13:e1006971. [PMID: 28873409 PMCID: PMC5600410 DOI: 10.1371/journal.pgen.1006971] [Citation(s) in RCA: 56] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2017] [Revised: 09/15/2017] [Accepted: 08/09/2017] [Indexed: 12/15/2022] Open
Abstract
The process of speciation involves populations diverging over time until they are genetically and reproductively isolated. Hybridization between nascent species was long thought to directly oppose speciation. However, the amount of interspecific genetic exchange (introgression) mediated by hybridization remains largely unknown, although recent progress in genome sequencing has made measuring introgression more tractable. A natural place to look for individuals with admixed ancestry (indicative of introgression) is in regions where species co-occur. In west Africa, D. santomea and D. yakuba hybridize on the island of São Tomé, while D. yakuba and D. teissieri hybridize on the nearby island of Bioko. In this report, we quantify the genomic extent of introgression between the three species of the Drosophila yakuba clade (D. yakuba, D. santomea), D. teissieri). We sequenced the genomes of 86 individuals from all three species. We also developed and applied a new statistical framework, using a hidden Markov approach, to identify introgression. We found that introgression has occurred between both species pairs but most introgressed segments are small (on the order of a few kilobases). After ruling out the retention of ancestral polymorphism as an explanation for these similar regions, we find that the sizes of introgressed haplotypes indicate that genetic exchange is not recent (>1,000 generations ago). We additionally show that in both cases, introgression was rarer on X chromosomes than on autosomes which is consistent with sex chromosomes playing a large role in reproductive isolation. Even though the two species pairs have stable contemporary hybrid zones, providing the opportunity for ongoing gene flow, our results indicate that genetic exchange between these species is currently rare.
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Affiliation(s)
- David A. Turissini
- Biology Department, University of North Carolina, Chapel Hill, Chapel Hill, North Carolina, United States of America
| | - Daniel R. Matute
- Biology Department, University of North Carolina, Chapel Hill, Chapel Hill, North Carolina, United States of America
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Zancolli G, Baker TG, Barlow A, Bradley RK, Calvete JJ, Carter KC, de Jager K, Owens JB, Price JF, Sanz L, Scholes-Higham A, Shier L, Wood L, Wüster CE, Wüster W. Is Hybridization a Source of Adaptive Venom Variation in Rattlesnakes? A Test, Using a Crotalus scutulatus × viridis Hybrid Zone in Southwestern New Mexico. Toxins (Basel) 2016; 8:toxins8060188. [PMID: 27322321 PMCID: PMC4926154 DOI: 10.3390/toxins8060188] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Revised: 06/02/2016] [Accepted: 06/09/2016] [Indexed: 11/16/2022] Open
Abstract
Venomous snakes often display extensive variation in venom composition both between and within species. However, the mechanisms underlying the distribution of different toxins and venom types among populations and taxa remain insufficiently known. Rattlesnakes (Crotalus, Sistrurus) display extreme inter- and intraspecific variation in venom composition, centered particularly on the presence or absence of presynaptically neurotoxic phospholipases A₂ such as Mojave toxin (MTX). Interspecific hybridization has been invoked as a mechanism to explain the distribution of these toxins across rattlesnakes, with the implicit assumption that they are adaptively advantageous. Here, we test the potential of adaptive hybridization as a mechanism for venom evolution by assessing the distribution of genes encoding the acidic and basic subunits of Mojave toxin across a hybrid zone between MTX-positive Crotalus scutulatus and MTX-negative C. viridis in southwestern New Mexico, USA. Analyses of morphology, mitochondrial and single copy-nuclear genes document extensive admixture within a narrow hybrid zone. The genes encoding the two MTX subunits are strictly linked, and found in most hybrids and backcrossed individuals, but not in C. viridis away from the hybrid zone. Presence of the genes is invariably associated with presence of the corresponding toxin in the venom. We conclude that introgression of highly lethal neurotoxins through hybridization is not necessarily favored by natural selection in rattlesnakes, and that even extensive hybridization may not lead to introgression of these genes into another species.
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Affiliation(s)
- Giulia Zancolli
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Timothy G Baker
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Axel Barlow
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
- Evolutionary and Adaptive Genomics Group, Institute for Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, Haus 29, 14476 Potsdam (Golm), Germany.
| | - Rebecca K Bradley
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Juan J Calvete
- Venomics and Structural Proteomics Laboratory, Instituto de Biomedicina de Valencia, Consejo Superior de Investigaciones Científicas (CSIC), Jaume Roig 11, 46010 Valencia, Spain.
| | - Kimberley C Carter
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Kaylah de Jager
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - John Benjamin Owens
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Jenny Forrester Price
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Libia Sanz
- Venomics and Structural Proteomics Laboratory, Instituto de Biomedicina de Valencia, Consejo Superior de Investigaciones Científicas (CSIC), Jaume Roig 11, 46010 Valencia, Spain.
| | - Amy Scholes-Higham
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Liam Shier
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Liam Wood
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Catharine E Wüster
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Wolfgang Wüster
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
- Chiricahua Desert Museum, P.O. Box 376, Rodeo, NM 88056, USA.
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Christe C, Stölting KN, Bresadola L, Fussi B, Heinze B, Wegmann D, Lexer C. Selection against recombinant hybrids maintains reproductive isolation in hybridizingPopulusspecies despite F1fertility and recurrent gene flow. Mol Ecol 2016; 25:2482-98. [DOI: 10.1111/mec.13587] [Citation(s) in RCA: 72] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Revised: 01/31/2016] [Accepted: 02/02/2016] [Indexed: 12/31/2022]
Affiliation(s)
- Camille Christe
- Department of Biology; University of Fribourg; Chemin du Musée 10 CH-1700 Fribourg Switzerland
| | - Kai N. Stölting
- Department of Biology; University of Fribourg; Chemin du Musée 10 CH-1700 Fribourg Switzerland
| | - Luisa Bresadola
- Department of Biology; University of Fribourg; Chemin du Musée 10 CH-1700 Fribourg Switzerland
| | - Barbara Fussi
- Applied Forest Genetics; Bavarian Office for Forest Seeding and Planting; Forstamtsplatz 1 83317 Teisendorf Germany
| | - Berthold Heinze
- Department of Genetics; Austrian Federal Research and Training Centre for Forests; Natural Hazards and Landscape; Seckendorff-Gudent-Weg 8 A-1130 Vienna Austria
| | - Daniel Wegmann
- Department of Biology; University of Fribourg; Chemin du Musée 10 CH-1700 Fribourg Switzerland
| | - Christian Lexer
- Department of Biology; University of Fribourg; Chemin du Musée 10 CH-1700 Fribourg Switzerland
- Department of Botany and Biodiversity Research; University of Vienna; Rennweg 14 A-1030 Vienna Austria
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The Role of Recombination in Evolutionary Rescue. Genetics 2015; 202:721-32. [PMID: 26627842 DOI: 10.1534/genetics.115.180299] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2015] [Accepted: 11/16/2015] [Indexed: 11/18/2022] Open
Abstract
How likely is it that a population escapes extinction through adaptive evolution? The answer to this question is of great relevance in conservation biology, where we aim at species' rescue and the maintenance of biodiversity, and in agriculture and medicine, where we seek to hamper the emergence of pesticide or drug resistance. By reshuffling the genome, recombination has two antagonistic effects on the probability of evolutionary rescue: it generates and it breaks up favorable gene combinations. Which of the two effects prevails depends on the fitness effects of mutations and on the impact of stochasticity on the allele frequencies. In this article, we analyze a mathematical model for rescue after a sudden environmental change when adaptation is contingent on mutations at two loci. The analysis reveals a complex nonlinear dependence of population survival on recombination. We moreover find that, counterintuitively, a fast eradication of the wild type can promote rescue in the presence of recombination. The model also shows that two-step rescue is not unlikely to happen and can even be more likely than single-step rescue (where adaptation relies on a single mutation), depending on the circumstances.
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Main BJ, Lee Y, Collier TC, Norris LC, Brisco K, Fofana A, Cornel AJ, Lanzaro GC. Complex genome evolution in Anopheles coluzzii associated with increased insecticide usage in Mali. Mol Ecol 2015; 24:5145-57. [PMID: 26359110 PMCID: PMC4615556 DOI: 10.1111/mec.13382] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2014] [Revised: 08/07/2015] [Accepted: 08/21/2015] [Indexed: 01/01/2023]
Abstract
In certain cases, a species may have access to important genetic variation present in a related species via adaptive introgression. These novel alleles may interact with their new genetic background, resulting in unexpected phenotypes. In this study, we describe a selective sweep on standing variation on the X chromosome in the mosquito Anopheles coluzzii, a principal malaria vector in West Africa. This event may have been influenced by the recent adaptive introgression of the insecticide resistance gene known as kdr from the sister species Anopheles gambiae. Individuals carrying both kdr and a nearly fixed X-linked haplotype, encompassing at least four genes including the P450 gene CYP9K1 and the cuticular protein CPR125, have rapidly increased in relative frequency. In parallel, a reproductively isolated insecticide-susceptible A. gambiae population (Bamako form) has been driven to local extinction, likely due to strong selection from increased insecticide-treated bed net usage.
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Affiliation(s)
- Bradley J Main
- Vector Genetics Laboratory, UC Davis, 1089 Veterinary Medicine Dr, 4225 VM3B, Davis, CA, 95616, USA.,Department of Pathology, Microbiology and Immunology, UC Davis, 1089 Veterinary Medicine Dr, 4225 VM3B, Davis, CA, 95616, USA
| | - Yoosook Lee
- Vector Genetics Laboratory, UC Davis, 1089 Veterinary Medicine Dr, 4225 VM3B, Davis, CA, 95616, USA.,Department of Pathology, Microbiology and Immunology, UC Davis, 1089 Veterinary Medicine Dr, 4225 VM3B, Davis, CA, 95616, USA
| | - Travis C Collier
- Vector Genetics Laboratory, UC Davis, 1089 Veterinary Medicine Dr, 4225 VM3B, Davis, CA, 95616, USA.,Department of Pathology, Microbiology and Immunology, UC Davis, 1089 Veterinary Medicine Dr, 4225 VM3B, Davis, CA, 95616, USA
| | - Laura C Norris
- Vector Genetics Laboratory, UC Davis, 1089 Veterinary Medicine Dr, 4225 VM3B, Davis, CA, 95616, USA.,Department of Pathology, Microbiology and Immunology, UC Davis, 1089 Veterinary Medicine Dr, 4225 VM3B, Davis, CA, 95616, USA
| | - Katherine Brisco
- Department of Entomology and Nematology, University of California, Davis, CA, 95616, USA
| | - Abdrahamane Fofana
- Malaria Research and Training Center, University of Bamako, BP 1805, Bamako, Mali
| | - Anthony J Cornel
- Vector Genetics Laboratory, UC Davis, 1089 Veterinary Medicine Dr, 4225 VM3B, Davis, CA, 95616, USA.,Department of Entomology and Nematology, University of California, Davis, CA, 95616, USA
| | - Gregory C Lanzaro
- Vector Genetics Laboratory, UC Davis, 1089 Veterinary Medicine Dr, 4225 VM3B, Davis, CA, 95616, USA.,Department of Pathology, Microbiology and Immunology, UC Davis, 1089 Veterinary Medicine Dr, 4225 VM3B, Davis, CA, 95616, USA
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