1
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Thomson L, Espinosa DP, Brandvain Y, Van Cleve J. Linked selection and the evolution of altruism in family-structured populations. Ecol Evol 2024; 14:e10980. [PMID: 38371869 PMCID: PMC10870336 DOI: 10.1002/ece3.10980] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Revised: 01/12/2024] [Accepted: 01/29/2024] [Indexed: 02/20/2024] Open
Abstract
Much research on the evolution of altruism via kin selection, group selection, and reciprocity focuses on the role of a single locus or quantitative trait. Very few studies have explored how linked selection, or selection at loci neighboring an altruism locus, impacts the evolution of altruism. While linked selection can decrease the efficacy of selection at neighboring loci, it might have other effects including promoting selection for altruism by increasing relatedness in regions of low recombination. Here, we used population genetic simulations to study how negative selection at linked loci, or background selection, affects the evolution of altruism. When altruism occurs between full siblings, we found that background selection interfered with selection on the altruistic allele, increasing its fixation probability when the altruistic allele was disfavored and reducing its fixation when the allele was favored. In other words, background selection has the same effect on altruistic genes in family-structured populations as it does on other, nonsocial, genes. This contrasts with prior research showing that linked selective sweeps can favor the evolution of cooperation, and we discuss possibilities for resolving these contrasting results.
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Affiliation(s)
- Lia Thomson
- Department of Plant and Microbial BiologyUniversity of MinnesotaSt. PaulMinnesotaUSA
| | | | - Yaniv Brandvain
- Department of Plant and Microbial BiologyUniversity of MinnesotaSt. PaulMinnesotaUSA
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2
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Bock DG, Cai Z, Elphinstone C, González-Segovia E, Hirabayashi K, Huang K, Keais GL, Kim A, Owens GL, Rieseberg LH. Genomics of plant speciation. PLANT COMMUNICATIONS 2023; 4:100599. [PMID: 37050879 PMCID: PMC10504567 DOI: 10.1016/j.xplc.2023.100599] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Revised: 03/21/2023] [Accepted: 04/06/2023] [Indexed: 06/19/2023]
Abstract
Studies of plants have been instrumental for revealing how new species originate. For several decades, botanical research has complemented and, in some cases, challenged concepts on speciation developed via the study of other organisms while also revealing additional ways in which species can form. Now, the ability to sequence genomes at an unprecedented pace and scale has allowed biologists to settle decades-long debates and tackle other emerging challenges in speciation research. Here, we review these recent genome-enabled developments in plant speciation. We discuss complications related to identification of reproductive isolation (RI) loci using analyses of the landscape of genomic divergence and highlight the important role that structural variants have in speciation, as increasingly revealed by new sequencing technologies. Further, we review how genomics has advanced what we know of some routes to new species formation, like hybridization or whole-genome duplication, while casting doubt on others, like population bottlenecks and genetic drift. While genomics can fast-track identification of genes and mutations that confer RI, we emphasize that follow-up molecular and field experiments remain critical. Nonetheless, genomics has clarified the outsized role of ancient variants rather than new mutations, particularly early during speciation. We conclude by highlighting promising avenues of future study. These include expanding what we know so far about the role of epigenetic and structural changes during speciation, broadening the scope and taxonomic breadth of plant speciation genomics studies, and synthesizing information from extensive genomic data that have already been generated by the plant speciation community.
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Affiliation(s)
- Dan G Bock
- Department of Botany and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada
| | - Zhe Cai
- Department of Botany and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada
| | - Cassandra Elphinstone
- Department of Botany and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada
| | - Eric González-Segovia
- Department of Botany and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada
| | | | - Kaichi Huang
- Department of Botany and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada
| | - Graeme L Keais
- Department of Botany and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada
| | - Amy Kim
- Department of Botany and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada
| | - Gregory L Owens
- Department of Biology, University of Victoria, Victoria, BC, Canada
| | - Loren H Rieseberg
- Department of Botany and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada.
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3
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Wong ELY, Filatov DA. The role of recombination landscape in species hybridisation and speciation. FRONTIERS IN PLANT SCIENCE 2023; 14:1223148. [PMID: 37484464 PMCID: PMC10361763 DOI: 10.3389/fpls.2023.1223148] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/15/2023] [Accepted: 06/13/2023] [Indexed: 07/25/2023]
Abstract
It is now well recognised that closely related species can hybridize and exchange genetic material, which may promote or oppose adaptation and speciation. In some cases, interspecific hybridisation is very common, making it surprising that species identity is preserved despite active gene exchange. The genomes of most eukaryotic species are highly heterogeneous with regard to gene density, abundance of repetitive DNA, chromatin compactisation etc, which can make certain genomic regions more prone or more resistant to introgression of genetic material from other species. Heterogeneity in local recombination rate underpins many of the observed patterns across the genome (e.g. actively recombining regions are typically gene rich and depleted for repetitive DNA) and it can strongly affect the permeability of genomic regions to interspecific introgression. The larger the region lacking recombination, the higher the chance for the presence of species incompatibility gene(s) in that region, making the entire non- or rarely recombining block impermeable to interspecific introgression. Large plant genomes tend to have highly heterogeneous recombination landscape, with recombination frequently occurring at the ends of the chromosomes and central regions lacking recombination. In this paper we review the relationship between recombination and introgression in plants and argue that large rarely recombining regions likely play a major role in preserving species identity in actively hybridising plant species.
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Affiliation(s)
- Edgar L. Y. Wong
- Department of Biology, University of Oxford, Oxford, United Kingdom
- Senckenberg Biodiversity and Climate Research Centre, Frankfurt am Main, Germany
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4
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Friedlander E, Steinrücken M. A numerical framework for genetic hitchhiking in populations of variable size. Genetics 2022; 220:6526396. [PMID: 35143667 PMCID: PMC8893261 DOI: 10.1093/genetics/iyac012] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Accepted: 12/27/2021] [Indexed: 11/13/2022] Open
Abstract
Natural selection on beneficial or deleterious alleles results in an increase or decrease, respectively, of their frequency within the population. Due to chromosomal linkage, the dynamics of the selected site affect the genetic variation at nearby neutral loci in a process commonly referred to as genetic hitchhiking. Changes in population size, however, can yield patterns in genomic data that mimic the effects of selection. Accurately modeling these dynamics is thus crucial to understanding how selection and past population size changes impact observed patterns of genetic variation. Here, we model the evolution of haplotype frequencies with the Wright-Fisher diffusion to study the impact of selection on linked neutral variation. Explicit solutions are not known for the dynamics of this diffusion when selection and recombination act simultaneously. Thus, we present a method for numerically evaluating the Wright-Fisher diffusion dynamics of 2 linked loci separated by a certain recombination distance when selection is acting. We can account for arbitrary population size histories explicitly using this approach. A key step in the method is to express the moments of the associated transition density, or sampling probabilities, as solutions to ordinary differential equations. Numerically solving these differential equations relies on a novel accurate and numerically efficient technique to estimate higher order moments from lower order moments. We demonstrate how this numerical framework can be used to quantify the reduction and recovery of genetic diversity around a selected locus over time and elucidate distortions in the site-frequency-spectra of neutral variation linked to loci under selection in various demographic settings. The method can be readily extended to more general modes of selection and applied in likelihood frameworks to detect loci under selection and infer the strength of the selective pressure.
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Affiliation(s)
- Eric Friedlander
- Department of Ecology and Evolution, University of Chicago, Chicago, IL 60637, USA,Department of Mathematics, Saint Norbert College, Green Bay, WI 54115, USA
| | - Matthias Steinrücken
- Department of Ecology and Evolution, University of Chicago, Chicago, IL 60637, USA,Department of Human Genetics, University of Chicago, Chicago, IL 60637, USA,Corresponding author: Department of Ecology & Evolution, The University of Chicago, 1101 E. 57th Street, Chicago, IL 60637, USA.
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5
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Zeng K, Charlesworth B, Hobolth A. Studying models of balancing selection using phase-type theory. Genetics 2021; 218:6237896. [PMID: 33871627 DOI: 10.1093/genetics/iyab055] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2021] [Accepted: 03/25/2021] [Indexed: 11/15/2022] Open
Abstract
Balancing selection (BLS) is the evolutionary force that maintains high levels of genetic variability in many important genes. To further our understanding of its evolutionary significance, we analyze models with BLS acting on a biallelic locus: an equilibrium model with long-term BLS, a model with long-term BLS and recent changes in population size, and a model of recent BLS. Using phase-type theory, a mathematical tool for analyzing continuous time Markov chains with an absorbing state, we examine how BLS affects polymorphism patterns in linked neutral regions, as summarized by nucleotide diversity, the expected number of segregating sites, the site frequency spectrum, and the level of linkage disequilibrium (LD). Long-term BLS affects polymorphism patterns in a relatively small genomic neighborhood, and such selection targets are easier to detect when the equilibrium frequencies of the selected variants are close to 50%, or when there has been a population size reduction. For a new mutation subject to BLS, its initial increase in frequency in the population causes linked neutral regions to have reduced diversity, an excess of both high and low frequency derived variants, and elevated LD with the selected locus. These patterns are similar to those produced by selective sweeps, but the effects of recent BLS are weaker. Nonetheless, compared to selective sweeps, nonequilibrium polymorphism and LD patterns persist for a much longer period under recent BLS, which may increase the chance of detecting such selection targets. An R package for analyzing these models, among others (e.g., isolation with migration), is available.
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Affiliation(s)
- Kai Zeng
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, UK
| | - Brian Charlesworth
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3FL, UK
| | - Asger Hobolth
- Department of Mathematics, Aarhus University, Aarhus DK-8000, Denmark
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6
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Booker TR, Yeaman S, Whitlock MC. Global adaptation complicates the interpretation of genome scans for local adaptation. Evol Lett 2020; 5:4-15. [PMID: 33552532 PMCID: PMC7857299 DOI: 10.1002/evl3.208] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Revised: 10/27/2020] [Accepted: 11/12/2020] [Indexed: 12/14/2022] Open
Abstract
Spatially varying selection promotes variance in allele frequencies, increasing genetic differentiation between the demes of a metapopulation. For that reason, outliers in the genome‐wide distribution of summary statistics measuring genetic differentiation, such as FST, are often interpreted as evidence for alleles that contribute to local adaptation. However, theoretical studies have shown that in spatially structured populations the spread of beneficial mutations with spatially uniform fitness effects can also induce transient genetic differentiation. In recent years, numerous empirical studies have suggested that such species‐wide, or global, adaptation makes a substantial contribution to molecular evolution. In this perspective, we discuss how commonly such global adaptation may influence the genome‐wide distribution of FST and generate genetic differentiation patterns, which could be mistaken for local adaptation. To illustrate this, we use forward‐in‐time population genetic simulations assuming parameters for the rate and strength of beneficial mutations consistent with estimates from natural populations. We demonstrate that the spread of globally beneficial mutations in parapatric populations may frequently generate FST outliers, which could be misinterpreted as evidence for local adaptation. The spread of beneficial mutations causes selective sweeps at flanking sites, so in some cases, the effects of global versus local adaptation may be distinguished by examining patterns of nucleotide diversity within and between populations in addition to FST. However, when local adaptation has been only recently established, it may be much more difficult to distinguish from global adaptation, due to less accumulation of linkage disequilibrium at flanking sites. Through our discussion, we conclude that a large fraction of FST outliers that are presumed to arise from local adaptation may instead be due to global adaptation.
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Affiliation(s)
- Tom R Booker
- Department of Forest and Conservation Sciences University of British Columbia Vancouver Canada.,Biodiversity Research Centre University of British Columbia Vancouver Canada
| | - Sam Yeaman
- Department of Biological Sciences University of Calgary Calgary Canada
| | - Michael C Whitlock
- Biodiversity Research Centre University of British Columbia Vancouver Canada.,Department of Zoology University of British Columbia Vancouver Canada
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7
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Matthey‐Doret R, Whitlock MC. Background selection andFST: Consequences for detecting local adaptation. Mol Ecol 2019; 28:3902-3914. [DOI: 10.1111/mec.15197] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2018] [Revised: 06/19/2019] [Accepted: 07/03/2019] [Indexed: 01/03/2023]
Affiliation(s)
- Remi Matthey‐Doret
- Department of Zoology and Biodiversity Research Centre University of British Columbia Vancouver BC Canada
| | - Michael C. Whitlock
- Department of Zoology and Biodiversity Research Centre University of British Columbia Vancouver BC Canada
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8
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Zeng K, Jackson BC, Barton HJ. Methods for Estimating Demography and Detecting Between-Locus Differences in the Effective Population Size and Mutation Rate. Mol Biol Evol 2019; 36:423-433. [PMID: 30428070 PMCID: PMC6409433 DOI: 10.1093/molbev/msy212] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
It is known that the effective population size (Ne) and the mutation rate (u) vary across the genome. Here, we show that ignoring this heterogeneity may lead to biased estimates of past demography. To solve the problem, we develop new methods for jointly inferring past changes in population size and detecting variation in Ne and u between loci. These methods rely on either polymorphism data alone or both polymorphism and divergence data. In addition to inferring demography, we can use the methods to study a variety of questions: 1) comparing sex chromosomes with autosomes (for finding evidence for male-driven evolution, an unequal sex ratio, or sex-biased demographic changes) and 2) analyzing multilocus data from within autosomes or sex chromosomes (for studying determinants of variability in Ne and u). Simulations suggest that the methods can provide accurate parameter estimates and have substantial statistical power for detecting difference in Ne and u. As an example, we use the methods to analyze a polymorphism data set from Drosophila simulans. We find clear evidence for rapid population expansion. The results also indicate that the autosomes have a higher mutation rate than the X chromosome and that the sex ratio is probably female-biased. The new methods have been implemented in a user-friendly package.
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Affiliation(s)
- Kai Zeng
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield, United Kingdom
| | - Benjamin C Jackson
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Henry J Barton
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield, United Kingdom
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9
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Irwin DE, Milá B, Toews DPL, Brelsford A, Kenyon HL, Porter AN, Grossen C, Delmore KE, Alcaide M, Irwin JH. A comparison of genomic islands of differentiation across three young avian species pairs. Mol Ecol 2018; 27:4839-4855. [PMID: 30187980 DOI: 10.1111/mec.14858] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Revised: 07/10/2018] [Accepted: 07/14/2018] [Indexed: 02/06/2023]
Abstract
Detailed evaluations of genomic variation between sister species often reveal distinct chromosomal regions of high relative differentiation (i.e., "islands of differentiation" in FST ), but there is much debate regarding the causes of this pattern. We briefly review the prominent models of genomic islands of differentiation and compare patterns of genomic differentiation in three closely related pairs of New World warblers with the goal of evaluating support for the four models. Each pair (MacGillivray's/mourning warblers; Townsend's/black-throated green warblers; and Audubon's/myrtle warblers) consists of forms that were likely separated in western and eastern North American refugia during cycles of Pleistocene glaciations and have now come into contact in western Canada, where each forms a narrow hybrid zone. We show strong differences between pairs in their patterns of genomic heterogeneity in FST , suggesting differing selective forces and/or differing genomic responses to similar selective forces among the three pairs. Across most of the genome, levels of within-group nucleotide diversity (πWithin ) are almost as large as levels of between-group nucleotide distance (πBetween ) within each pair, suggesting recent common ancestry and/or gene flow. In two pairs, a pattern of the FST peaks having low πBetween suggests that selective sweeps spread between geographically differentiated groups, followed by local differentiation. This "sweep-before-differentiation" model is consistent with signatures of gene flow within the yellow-rumped warbler species complex. These findings add to our growing understanding of speciation as a complex process that can involve phases of adaptive introgression among partially differentiated populations.
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Affiliation(s)
- Darren E Irwin
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
| | - Borja Milá
- National Museum of Natural Sciences, Spanish National Research Council (CSIC), Madrid, Spain
| | - David P L Toews
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada.,Cornell Lab of Ornithology & Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York
| | - Alan Brelsford
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada.,Department of Evolution, Ecology and Organismal Biology, University of California, Riverside, California
| | - Haley L Kenyon
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada.,Department of Biology, Queen's University, Biosciences Complex, Kingston, Ontario, Canada
| | - Alison N Porter
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
| | - Christine Grossen
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada.,Department of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland
| | - Kira E Delmore
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada.,Max Planck Institute for Evolutionary Biology, Behavioural Genomics, Plön, Germany
| | - Miguel Alcaide
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada.,Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada
| | - Jessica H Irwin
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
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10
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Comeron JM. Background selection as null hypothesis in population genomics: insights and challenges from Drosophila studies. Philos Trans R Soc Lond B Biol Sci 2018; 372:rstb.2016.0471. [PMID: 29109230 PMCID: PMC5698629 DOI: 10.1098/rstb.2016.0471] [Citation(s) in RCA: 73] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/04/2017] [Indexed: 12/11/2022] Open
Abstract
The consequences of selection at linked sites are multiple and widespread across the genomes of most species. Here, I first review the main concepts behind models of selection and linkage in recombining genomes, present the difficulty in parametrizing these models simply as a reduction in effective population size (Ne) and discuss the predicted impact of recombination rates on levels of diversity across genomes. Arguments are then put forward in favour of using a model of selection and linkage with neutral and deleterious mutations (i.e. the background selection model, BGS) as a sensible null hypothesis for investigating the presence of other forms of selection, such as balancing or positive. I also describe and compare two studies that have generated high-resolution landscapes of the predicted consequences of selection at linked sites in Drosophila melanogaster. Both studies show that BGS can explain a very large fraction of the observed variation in diversity across the whole genome, thus supporting its use as null model. Finally, I identify and discuss a number of caveats and challenges in studies of genetic hitchhiking that have been often overlooked, with several of them sharing a potential bias towards overestimating the evidence supporting recent selective sweeps to the detriment of a BGS explanation. One potential source of bias is the analysis of non-equilibrium populations: it is precisely because models of selection and linkage predict variation in Ne across chromosomes that demographic dynamics are not expected to be equivalent chromosome- or genome-wide. Other challenges include the use of incomplete genome annotations, the assumption of temporally stable recombination landscapes, the presence of genes under balancing selection and the consequences of ignoring non-crossover (gene conversion) recombination events. This article is part of the themed issue ‘Evolutionary causes and consequences of recombination rate variation in sexual organisms’.
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Affiliation(s)
- Josep M Comeron
- Department of Biology, University of Iowa, Iowa City, IA 52242, USA .,Interdisciplinary Program in Genetics, University of Iowa, Iowa City, IA 52242, USA
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11
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The Effect of Strong Purifying Selection on Genetic Diversity. Genetics 2018; 209:1235-1278. [PMID: 29844134 DOI: 10.1534/genetics.118.301058] [Citation(s) in RCA: 121] [Impact Index Per Article: 20.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Accepted: 05/25/2018] [Indexed: 12/15/2022] Open
Abstract
Purifying selection reduces genetic diversity, both at sites under direct selection and at linked neutral sites. This process, known as background selection, is thought to play an important role in shaping genomic diversity in natural populations. Yet despite its importance, the effects of background selection are not fully understood. Previous theoretical analyses of this process have taken a backward-time approach based on the structured coalescent. While they provide some insight, these methods are either limited to very small samples or are computationally prohibitive. Here, we present a new forward-time analysis of the trajectories of both neutral and deleterious mutations at a nonrecombining locus. We find that strong purifying selection leads to remarkably rich dynamics: neutral mutations can exhibit sweep-like behavior, and deleterious mutations can reach substantial frequencies even when they are guaranteed to eventually go extinct. Our analysis of these dynamics allows us to calculate analytical expressions for the full site frequency spectrum. We find that whenever background selection is strong enough to lead to a reduction in genetic diversity, it also results in substantial distortions to the site frequency spectrum, which can mimic the effects of population expansions or positive selection. Because these distortions are most pronounced in the low and high frequency ends of the spectrum, they become particularly important in larger samples, but may have small effects in smaller samples. We also apply our forward-time framework to calculate other quantities, such as the ultimate fates of polymorphisms or the fitnesses of their ancestral backgrounds.
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12
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Irwin DE. Sex chromosomes and speciation in birds and other ZW systems. Mol Ecol 2018; 27:3831-3851. [PMID: 29443419 DOI: 10.1111/mec.14537] [Citation(s) in RCA: 65] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2017] [Revised: 02/03/2018] [Accepted: 02/06/2018] [Indexed: 01/01/2023]
Abstract
Theory and empirical patterns suggest a disproportionate role for sex chromosomes in evolution and speciation. Focusing on ZW sex determination (females ZW, males ZZ; the system in birds, many snakes, and lepidopterans), I review how evolutionary dynamics are expected to differ between the Z, W and the autosomes, discuss how these differences may lead to a greater role of the sex chromosomes in speciation and use data from birds to compare relative evolutionary rates of sex chromosomes and autosomes. Neutral mutations, partially or completely recessive beneficial mutations, and deleterious mutations under many conditions are expected to accumulate faster on the Z than on autosomes. Sexually antagonistic polymorphisms are expected to arise on the Z, raising the possibility of the spread of preference alleles. The faster accumulation of many types of mutations and the potential for complex evolutionary dynamics of sexually antagonistic traits and preferences contribute to a role for the Z chromosome in speciation. A quantitative comparison among a wide variety of bird species shows that the Z tends to have less within-population diversity and greater between-species differentiation than the autosomes, likely due to both adaptive evolution and a greater rate of fixation of deleterious alleles. The W chromosome also shows strong potential to be involved in speciation, in part because of its co-inheritance with the mitochondrial genome. While theory and empirical evidence suggest a disproportionate role for sex chromosomes in speciation, the importance of sex chromosomes is moderated by their small size compared to the whole genome.
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Affiliation(s)
- Darren E Irwin
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada
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13
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Svardal H, Jasinska AJ, Apetrei C, Coppola G, Huang Y, Schmitt CA, Jacquelin B, Ramensky V, Müller-Trutwin M, Antonio M, Weinstock G, Grobler JP, Dewar K, Wilson RK, Turner TR, Warren WC, Freimer NB, Nordborg M. Ancient hybridization and strong adaptation to viruses across African vervet monkey populations. Nat Genet 2017; 49:1705-1713. [PMID: 29083404 PMCID: PMC5709169 DOI: 10.1038/ng.3980] [Citation(s) in RCA: 89] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2016] [Accepted: 09/27/2017] [Indexed: 12/16/2022]
Abstract
Vervet monkeys are among the most widely distributed nonhuman primates, show considerable phenotypic diversity, and have long been an important biomedical model for a variety of human diseases and in vaccine research. Using whole-genome sequencing data from 163 vervets sampled from across Africa and the Caribbean, we find high diversity within and between taxa and clear evidence that taxonomic divergence was reticulate rather than following a simple branching pattern. A scan for diversifying selection across taxa identifies strong and highly polygenic selection signals affecting viral processes. Furthermore, selection scores are elevated in genes whose human orthologs interact with HIV and in genes that show a response to experimental simian immunodeficiency virus (SIV) infection in vervet monkeys but not in rhesus macaques, suggesting that part of the signal reflects taxon-specific adaptation to SIV.
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Affiliation(s)
- Hannes Svardal
- Gregor Mendel Institute, Austrian Academy of Sciences, Vienna Biocenter (VBC), Vienna, Austria
| | - Anna J Jasinska
- Center for Neurobehavioral Genetics, University of California Los Angeles, Los Angeles, USA
- Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland
| | - Cristian Apetrei
- Center for Vaccine Research, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
- Department of Microbiology and Molecular Genetics, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
| | - Giovanni Coppola
- Center for Neurobehavioral Genetics, University of California Los Angeles, Los Angeles, USA
- Department of Neurology, University of California Los Angeles, USA
| | - Yu Huang
- State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, China
| | | | | | - Vasily Ramensky
- Center for Neurobehavioral Genetics, University of California Los Angeles, Los Angeles, USA
- Moscow Institute of Physics and Technology, Dolgoprudny, Russia
| | | | - Martin Antonio
- Medical Research Council (MRC), The Gambia Unit, The Gambia
| | - George Weinstock
- The Jackson Laboratory for Genomic Medicine, Farmington, Connecticut, USA
| | - J Paul Grobler
- Department of Genetics, University of the Free State, Bloemfontein, South Africa
| | - Ken Dewar
- Department of Human Genetics, McGill University, Montreal, Quebec, Canada
| | - Richard K Wilson
- McDonnell Genome Institute, Washington University in St. Louis, St. Louis, USA
- Department of Anthropology, University of Wisconsin-Milwaukee, Milwaukee, USA
| | - Trudy R Turner
- Department of Genetics, University of the Free State, Bloemfontein, South Africa
| | - Wesley C Warren
- McDonnell Genome Institute, Washington University in St. Louis, St. Louis, USA
| | - Nelson B Freimer
- Center for Neurobehavioral Genetics, University of California Los Angeles, Los Angeles, USA
| | - Magnus Nordborg
- Gregor Mendel Institute, Austrian Academy of Sciences, Vienna Biocenter (VBC), Vienna, Austria
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14
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Ravinet M, Faria R, Butlin RK, Galindo J, Bierne N, Rafajlović M, Noor MAF, Mehlig B, Westram AM. Interpreting the genomic landscape of speciation: a road map for finding barriers to gene flow. J Evol Biol 2017; 30:1450-1477. [DOI: 10.1111/jeb.13047] [Citation(s) in RCA: 306] [Impact Index Per Article: 43.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2016] [Revised: 01/31/2017] [Accepted: 02/01/2017] [Indexed: 12/14/2022]
Affiliation(s)
- M. Ravinet
- Centre for Ecological and Evolutionary Synthesis; University of Oslo; Oslo Norway
- National Institute of Genetics; Mishima Shizuoka Japan
| | - R. Faria
- CIBIO, Centro de Investigação em Biodiversidade e Recursos Genéticos; InBIO, Laboratório Associado; Universidade do Porto; Vairão Portugal
- Department of Experimental and Health Sciences; IBE, Institute of Evolutionary Biology (CSIC-UPF); Pompeu Fabra University; Barcelona Spain
- Department of Animal and Plant Sciences; University of Sheffield; Sheffield UK
| | - R. K. Butlin
- Department of Animal and Plant Sciences; University of Sheffield; Sheffield UK
- Department of Marine Sciences; Centre for Marine Evolutionary Biology; University of Gothenburg; Gothenburg Sweden
| | - J. Galindo
- Department of Biochemistry, Genetics and Immunology; University of Vigo; Vigo Spain
| | - N. Bierne
- CNRS; Université Montpellier; ISEM; Station Marine Sète France
| | - M. Rafajlović
- Department of Physics; University of Gothenburg; Gothenburg Sweden
| | | | - B. Mehlig
- Department of Physics; University of Gothenburg; Gothenburg Sweden
| | - A. M. Westram
- Department of Animal and Plant Sciences; University of Sheffield; Sheffield UK
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15
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Burri R. Interpreting differentiation landscapes in the light of long-term linked selection. Evol Lett 2017. [DOI: 10.1002/evl3.14] [Citation(s) in RCA: 116] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Affiliation(s)
- Reto Burri
- Department of Population Ecology; Friedrich Schiller University Jena; Dornburger Strasse 159 D-07743 Jena Germany
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16
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Estimating the parameters of background selection and selective sweeps in Drosophila in the presence of gene conversion. Proc Natl Acad Sci U S A 2017; 114:E4762-E4771. [PMID: 28559322 DOI: 10.1073/pnas.1619434114] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
We used whole-genome resequencing data from a population of Drosophila melanogaster to investigate the causes of the negative correlation between the within-population synonymous nucleotide site diversity (πS ) of a gene and its degree of divergence from related species at nonsynonymous nucleotide sites (KA ). By using the estimated distributions of mutational effects on fitness at nonsynonymous and UTR sites, we predicted the effects of background selection at sites within a gene on πS and found that these could account for only part of the observed correlation between πS and KA We developed a model of the effects of selective sweeps that included gene conversion as well as crossing over. We used this model to estimate the average strength of selection on positively selected mutations in coding sequences and in UTRs, as well as the proportions of new mutations that are selectively advantageous. Genes with high levels of selective constraint on nonsynonymous sites were found to have lower strengths of positive selection and lower proportions of advantageous mutations than genes with low levels of constraint. Overall, background selection and selective sweeps within a typical gene reduce its synonymous diversity to ∼75% of its value in the absence of selection, with larger reductions for genes with high KA Gene conversion has a major effect on the estimates of the parameters of positive selection, such that the estimated strength of selection on favorable mutations is greatly reduced if it is ignored.
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17
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Lasne C, Sgrò CM, Connallon T. The Relative Contributions of the X Chromosome and Autosomes to Local Adaptation. Genetics 2017; 205:1285-1304. [PMID: 28064164 PMCID: PMC5340339 DOI: 10.1534/genetics.116.194670] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Accepted: 12/25/2016] [Indexed: 01/07/2023] Open
Abstract
Models of sex chromosome and autosome evolution yield key predictions about the genomic basis of adaptive divergence, and such models have been important in guiding empirical research in comparative genomics and studies of speciation. In addition to the adaptive differentiation that occurs between species over time, selection also favors genetic divergence across geographic space, with subpopulations of single species evolving conspicuous differences in traits involved in adaptation to local environmental conditions. The potential contribution of sex chromosomes (the X or Z) to local adaptation remains unclear, as we currently lack theory that directly links spatial variation in selection to local adaptation of X-linked and autosomal genes. Here, we develop population genetic models that explicitly consider the effects of genetic dominance, effective population size, and sex-specific migration and selection on the relative contributions of X-linked and autosomal genes to local adaptation. We show that X-linked genes should nearly always disproportionately contribute to local adaptation in the presence of gene flow. We also show that considerations of dominance and effective population size-which play pivotal roles in the theory of faster-X adaptation between species-have surprisingly little influence on the relative contribution of the X chromosome to local adaptation. Instead, sex-biased migration is the primary mediator of the strength of spatial large-X effects. Our results yield novel predictions about the role of sex chromosomes in local adaptation. We outline empirical approaches in evolutionary quantitative genetics and genomics that could build upon this new theory.
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Affiliation(s)
- Clémentine Lasne
- School of Biological Sciences, Monash University, Clayton 3800, Australia
| | - Carla M Sgrò
- School of Biological Sciences, Monash University, Clayton 3800, Australia
| | - Tim Connallon
- School of Biological Sciences, Monash University, Clayton 3800, Australia
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18
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Irwin DE, Alcaide M, Delmore KE, Irwin JH, Owens GL. Recurrent selection explains parallel evolution of genomic regions of high relative but low absolute differentiation in a ring species. Mol Ecol 2016; 25:4488-507. [PMID: 27484941 DOI: 10.1111/mec.13792] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Revised: 07/21/2016] [Accepted: 07/25/2016] [Indexed: 12/13/2022]
Abstract
Recent technological developments allow investigation of the repeatability of evolution at the genomic level. Such investigation is particularly powerful when applied to a ring species, in which spatial variation represents changes during the evolution of two species from one. We examined genomic variation among three subspecies of the greenish warbler ring species, using genotypes at 13 013 950 nucleotide sites along a new greenish warbler consensus genome assembly. Genomic regions of low within-group variation are remarkably consistent between the three populations. These regions show high relative differentiation but low absolute differentiation between populations. Comparisons with outgroup species show the locations of these peaks of relative differentiation are not well explained by phylogenetically conserved variation in recombination rates or selection. These patterns are consistent with a model in which selection in an ancestral form has reduced variation at some parts of the genome, and those same regions experience recurrent selection that subsequently reduces variation within each subspecies. The degree of heterogeneity in nucleotide diversity is greater than explained by models of background selection, but is consistent with selective sweeps. Given the evidence that greenish warblers have had both population differentiation for a long period of time and periods of gene flow between those populations, we propose that some genomic regions underwent selective sweeps over a broad geographic area followed by within-population selection-induced reductions in variation. An important implication of this 'sweep-before-differentiation' model is that genomic regions of high relative differentiation may have moved among populations more recently than other genomic regions.
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Affiliation(s)
- Darren E Irwin
- Department of Zoology and Biodiversity Research Center, University of British Columbia, 6270 University Blvd., Vancouver, BC, V6T 1Z4, Canada.
| | - Miguel Alcaide
- Department of Zoology and Biodiversity Research Center, University of British Columbia, 6270 University Blvd., Vancouver, BC, V6T 1Z4, Canada
| | - Kira E Delmore
- Department of Zoology and Biodiversity Research Center, University of British Columbia, 6270 University Blvd., Vancouver, BC, V6T 1Z4, Canada
| | - Jessica H Irwin
- Department of Zoology and Biodiversity Research Center, University of British Columbia, 6270 University Blvd., Vancouver, BC, V6T 1Z4, Canada
| | - Gregory L Owens
- Department of Zoology and Biodiversity Research Center, University of British Columbia, 6270 University Blvd., Vancouver, BC, V6T 1Z4, Canada
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