1
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Schneemann H, De Sanctis B, Welch JJ. Fisher's Geometric Model as a Tool to Study Speciation. Cold Spring Harb Perspect Biol 2024; 16:a041442. [PMID: 38253415 PMCID: PMC11216183 DOI: 10.1101/cshperspect.a041442] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2024]
Abstract
Interactions between alleles and across environments play an important role in the fitness of hybrids and are at the heart of the speciation process. Fitness landscapes capture these interactions and can be used to model hybrid fitness, helping us to interpret empirical observations and clarify verbal models. Here, we review recent progress in understanding hybridization outcomes through Fisher's geometric model, an intuitive and analytically tractable fitness landscape that captures many fitness patterns observed across taxa. We use case studies to show how the model parameters can be estimated from different types of data and discuss how these estimates can be used to make inferences about the divergence history and genetic architecture. We also highlight some areas where the model's predictions differ from alternative incompatibility-based models, such as the snowball effect and outlier patterns in genome scans.
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Affiliation(s)
- Hilde Schneemann
- Department of Genetics, University of Cambridge, Cambridge CB2 3EH, United Kingdom
| | - Bianca De Sanctis
- Department of Genetics, University of Cambridge, Cambridge CB2 3EH, United Kingdom
- Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, United Kingdom
| | - John J Welch
- Department of Genetics, University of Cambridge, Cambridge CB2 3EH, United Kingdom
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2
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Jahner JP, Parchman TL, Matocq MD. Multigenerational backcrossing and introgression between two woodrat species at an abrupt ecological transition. Mol Ecol 2021; 30:4245-4258. [PMID: 34219316 DOI: 10.1111/mec.16056] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Accepted: 06/28/2021] [Indexed: 12/27/2022]
Abstract
When organisms experience secondary contact after allopatric divergence, genomic regions can introgress differentially depending on their relationships with adaptation, reproductive isolation, recombination, and drift. Analyses of genome-wide patterns of divergence and introgression could provide insight into the outcomes of hybridization and the potential relationship between allopatric divergence and reproductive isolation. Here, we generate population genetic data (26,262 SNPs; 353 individuals) using a reduced-representation sequencing approach to quantify patterns of ancestry, differentiation, and introgression between a pair of ecologically distinct mammals-the desert woodrat (N. lepida) and Bryant's woodrat (N. bryanti)-that hybridize at a sharp ecotone in southern California. Individual ancestry estimates confirmed that hybrids were rare in this bimodal hybrid zone, and entirely consisted of a few F1 individuals and a broad range of multigenerational backcrosses. Genomic cline analyses indicated more than half of loci had elevated introgression from one genomic background into the other. However, introgression was not associated with relative or absolute measures of divergence, and loci with extreme values for both were not typically found near detoxification enzymes previously implicated in dietary specialization for woodrats. The decoupling of differentiation and introgression suggests that processes other than adaptation, such as drift, may underlie the extreme clines at this contact zone.
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Affiliation(s)
- Joshua P Jahner
- Department of Biology, University of Nevada, Reno, Nevada, USA.,Department of Botany, University of Wyoming, Laramie, Wyoming, USA
| | - Thomas L Parchman
- Department of Biology, University of Nevada, Reno, Nevada, USA.,Program in Ecology, Evolution, and Conservation Biology, University of Nevada, Reno, Nevada, USA
| | - Marjorie D Matocq
- Program in Ecology, Evolution, and Conservation Biology, University of Nevada, Reno, Nevada, USA.,Department of Natural Resources and Environmental Science, University of Nevada, Reno, Nevada, USA
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3
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Martin SH, Davey JW, Salazar C, Jiggins CD. Recombination rate variation shapes barriers to introgression across butterfly genomes. PLoS Biol 2019; 17:e2006288. [PMID: 30730876 PMCID: PMC6366726 DOI: 10.1371/journal.pbio.2006288] [Citation(s) in RCA: 175] [Impact Index Per Article: 35.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2018] [Accepted: 01/07/2019] [Indexed: 12/30/2022] Open
Abstract
Hybridisation and introgression can dramatically alter the relationships among groups of species, leading to phylogenetic discordance across the genome and between populations. Introgression can also erode species differences over time, but selection against introgression at certain loci acts to maintain postmating species barriers. Theory predicts that species barriers made up of many loci throughout the genome should lead to a broad correlation between introgression and recombination rate, which determines the extent to which selection on deleterious foreign alleles will affect neutral alleles at physically linked loci. Here, we describe the variation in genealogical relationships across the genome among three species of Heliconius butterflies: H. melpomene (mel), H. cydno (cyd), and H. timareta (tim), using whole genomes of 92 individuals, and ask whether this variation can be explained by heterogeneous barriers to introgression. We find that species relationships vary predictably at the chromosomal scale. By quantifying recombination rate and admixture proportions, we then show that rates of introgression are predicted by variation in recombination rate. This implies that species barriers are highly polygenic, with selection acting against introgressed alleles across most of the genome. In addition, long chromosomes, which have lower recombination rates, produce stronger barriers on average than short chromosomes. Finally, we find a consistent difference between two species pairs on either side of the Andes, which suggests differences in the architecture of the species barriers. Our findings illustrate how the combined effects of hybridisation, recombination, and natural selection, acting at multitudes of loci over long periods, can dramatically sculpt the phylogenetic relationships among species.
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Affiliation(s)
- Simon H. Martin
- Department of Zoology, University of Cambridge, Cambridge, United Kingdom
| | - John W. Davey
- Department of Biology, University of York, York, United Kingdom
| | - Camilo Salazar
- Biology Program, Faculty of Natural Sciences and Mathematics, Universidad del Rosario, Bogota, Colombia
| | - Chris D. Jiggins
- Department of Zoology, University of Cambridge, Cambridge, United Kingdom
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4
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Westram AM, Ravinet M. Land ahoy? Navigating the genomic landscape of speciation while avoiding shipwreck. J Evol Biol 2018; 30:1522-1525. [PMID: 28786189 DOI: 10.1111/jeb.13129] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Accepted: 06/04/2017] [Indexed: 12/25/2022]
Affiliation(s)
- A M Westram
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield, UK
| | - M Ravinet
- Centre for Ecological and Evolutionary Synthesis, University of Oslo, Oslo, Norway
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5
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Simon A, Bierne N, Welch JJ. Coadapted genomes and selection on hybrids: Fisher's geometric model explains a variety of empirical patterns. Evol Lett 2018; 2:472-498. [PMID: 30283696 PMCID: PMC6145440 DOI: 10.1002/evl3.66] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Revised: 06/02/2018] [Accepted: 06/06/2018] [Indexed: 12/27/2022] Open
Abstract
Natural selection plays a variety of roles in hybridization, speciation, and admixture. Most research has focused on two extreme cases: crosses between closely related inbred lines, where hybrids are fitter than their parents, or crosses between effectively isolated species, where hybrids suffer severe breakdown. But many natural populations must fall into intermediate regimes, with multiple types of gene interaction, and these are more difficult to study. Here, we develop a simple fitness landscape model, and show that it naturally interpolates between previous modeling approaches, which were designed for the extreme cases, and invoke either mildly deleterious recessives, or discrete hybrid incompatibilities. Our model yields several new predictions, which we test with genomic data from Mytilus mussels, and published data from plants (Zea, Populus, and Senecio) and animals (Mus, Teleogryllus, and Drosophila). The predictions are generally supported, and the model explains a number of surprising empirical patterns. Our approach enables novel and complementary uses of genome-wide datasets, which do not depend on identifying outlier loci, or "speciation genes" with anomalous effects. Given its simplicity and flexibility, and its predictive successes with a wide range of data, the approach should be readily extendable to other outstanding questions in the study of hybridization.
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Affiliation(s)
- Alexis Simon
- Institut des Sciences de l'Évolution UMR5554, Université de MontpellierCNRS‐IRD‐EPHE‐UMFrance
- Department of GeneticsUniversity of CambridgeDowning St. CambridgeCB23EHUnited Kingdom
| | - Nicolas Bierne
- Institut des Sciences de l'Évolution UMR5554, Université de MontpellierCNRS‐IRD‐EPHE‐UMFrance
- Department of GeneticsUniversity of CambridgeDowning St. CambridgeCB23EHUnited Kingdom
| | - John J. Welch
- Department of GeneticsUniversity of CambridgeDowning St. CambridgeCB23EHUnited Kingdom
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6
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Ravinet M. Notes from a snail island: Littorinid evolution and adaptation. Mol Ecol 2018; 27:2781-2789. [PMID: 29802775 DOI: 10.1111/mec.14730] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2018] [Revised: 05/01/2018] [Accepted: 05/06/2018] [Indexed: 12/20/2022]
Abstract
The most successful study systems are built on a foundation of decades of research on the basic biology, ecology and life history of the organisms in question. Combined with new technologies, this can provide a formidable means to address important issues in evolutionary biology and molecular ecology. Littorinid marine snails are a good example of this, with a rich literature on their taxonomy, speciation, thermal tolerance and behavioural adaptations. In August 2017, an international meeting on Littorinid evolution was held at the Tjärnö Marine Research Laboratory in Western Sweden. In this meeting review, I provide a summary of some of the exciting work on parallel evolution, sexual selection and adaptation to environmental stress presented there. I argue that newly available genomic resources present an opportunity for integrating the traditionally divergent fields of speciation and environmental adaptation in Littorinid research.
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Affiliation(s)
- Mark Ravinet
- Centre for Ecological and Evolutionary Synthesis, University of Oslo, Oslo, Norway
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7
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Rafati N, Blanco-Aguiar JA, Rubin CJ, Sayyab S, Sabatino SJ, Afonso S, Feng C, Alves PC, Villafuerte R, Ferrand N, Andersson L, Carneiro M. A genomic map of clinal variation across the European rabbit hybrid zone. Mol Ecol 2018; 27:1457-1478. [PMID: 29359877 DOI: 10.1111/mec.14494] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2017] [Revised: 12/03/2017] [Accepted: 12/04/2017] [Indexed: 01/02/2023]
Abstract
Speciation is a process proceeding from weak to complete reproductive isolation. In this continuum, naturally hybridizing taxa provide a promising avenue for revealing the genetic changes associated with the incipient stages of speciation. To identify such changes between two subspecies of rabbits that display partial reproductive isolation, we studied patterns of allele frequency change across their hybrid zone using whole-genome sequencing. To connect levels and patterns of genetic differentiation with phenotypic manifestations of subfertility in hybrid rabbits, we further investigated patterns of gene expression in testis. Geographic cline analysis revealed 253 regions characterized by steep changes in allele frequency across their natural region of contact. This catalog of regions is likely to be enriched for loci implicated in reproductive barriers and yielded several insights into the evolution of hybrid dysfunction in rabbits: (i) incomplete reproductive isolation is likely governed by the effects of many loci, (ii) protein-protein interaction analysis suggest that genes within these loci interact more than expected by chance, (iii) regulatory variation is likely the primary driver of incompatibilities, and (iv) large chromosomal rearrangements appear not to be a major mechanism underlying incompatibilities or promoting isolation in the face of gene flow. We detected extensive misregulation of gene expression in testis of hybrid males, but not a statistical overrepresentation of differentially expressed genes in candidate regions. Our results also did not support an X chromosome-wide disruption of expression as observed in mice and cats, suggesting variation in the mechanistic basis of hybrid male reduced fertility among mammals.
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Affiliation(s)
- Nima Rafati
- Science for Life Laboratory Uppsala, Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden.,Science for Life Laboratory Uppsala, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden
| | - José A Blanco-Aguiar
- CIBIO/InBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade do Porto, Vairão, Portugal.,Instituto de Investigacion en Recursos Cinegéticos (IREC-CSIC-UCLM-JCCM), Ciudad Real, Spain
| | - Carl J Rubin
- Science for Life Laboratory Uppsala, Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden
| | - Shumaila Sayyab
- Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Uppsala, Sweden.,Research Center for Modeling and Simulation, National University of Sciences and Technology, Islamabad, Pakistan
| | - Stephen J Sabatino
- CIBIO/InBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade do Porto, Vairão, Portugal
| | - Sandra Afonso
- CIBIO/InBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade do Porto, Vairão, Portugal
| | - Chungang Feng
- Science for Life Laboratory Uppsala, Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden
| | - Paulo C Alves
- CIBIO/InBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade do Porto, Vairão, Portugal.,Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Porto, Portugal
| | | | - Nuno Ferrand
- CIBIO/InBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade do Porto, Vairão, Portugal.,Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Porto, Portugal.,Department of Zoology, Faculty of Sciences, University of Johannesburg, Auckland, South Africa
| | - Leif Andersson
- Science for Life Laboratory Uppsala, Department of Medical Biochemistry and Microbiology, Uppsala University, Uppsala, Sweden.,Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, Uppsala, Sweden.,Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Miguel Carneiro
- CIBIO/InBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos, Universidade do Porto, Vairão, Portugal.,Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Porto, Portugal
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8
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Heterogeneous Patterns of Genetic Diversity and Differentiation in European and Siberian Chiffchaff ( Phylloscopus collybita abietinus/P. tristis). G3-GENES GENOMES GENETICS 2017; 7:3983-3998. [PMID: 29054864 PMCID: PMC5714495 DOI: 10.1534/g3.117.300152] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Identification of candidate genes for trait variation in diverging lineages and characterization of mechanistic underpinnings of genome differentiation are key steps toward understanding the processes underlying the formation of new species. Hybrid zones provide a valuable resource for such investigations, since they allow us to study how genomes evolve as species exchange genetic material and to associate particular genetic regions with phenotypic traits of interest. Here, we use whole-genome resequencing of both allopatric and hybridizing populations of the European (Phylloscopus collybita abietinus) and the Siberian chiffchaff (P. tristis)—two recently diverged species which differ in morphology, plumage, song, habitat, and migration—to quantify the regional variation in genome-wide genetic diversity and differentiation, and to identify candidate regions for trait variation. We find that the levels of diversity, differentiation, and divergence are highly heterogeneous, with significantly reduced global differentiation, and more pronounced differentiation peaks in sympatry than in allopatry. This pattern is consistent with regional differences in effective population size and recurrent background selection or selective sweeps reducing the genetic diversity in specific regions prior to lineage divergence, but the data also suggest that postdivergence selection has resulted in increased differentiation and fixed differences in specific regions. We find that hybridization and backcrossing is common in sympatry, and that phenotype is a poor predictor of the genomic composition of sympatric birds. The combination of a differentiation scan approach with identification of fixed differences pinpoint a handful of candidate regions that might be important for trait variation between the two species.
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