151
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Alves I, Arenas M, Currat M, Sramkova Hanulova A, Sousa VC, Ray N, Excoffier L. Long-Distance Dispersal Shaped Patterns of Human Genetic Diversity in Eurasia. Mol Biol Evol 2015; 33:946-58. [PMID: 26637555 PMCID: PMC4776706 DOI: 10.1093/molbev/msv332] [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] [Indexed: 12/11/2022] Open
Abstract
Most previous attempts at reconstructing the past history of human populations did not explicitly take geography into account or considered very simple scenarios of migration and ignored environmental information. However, it is likely that the last glacial maximum (LGM) affected the demography and the range of many species, including our own. Moreover, long-distance dispersal (LDD) may have been an important component of human migrations, allowing fast colonization of new territories and preserving high levels of genetic diversity. Here, we use a high-quality microsatellite data set genotyped in 22 populations to estimate the posterior probabilities of several scenarios for the settlement of the Old World by modern humans. We considered models ranging from a simple spatial expansion to others including LDD and a LGM-induced range contraction, as well as Neolithic demographic expansions. We find that scenarios with LDD are much better supported by data than models without LDD. Nevertheless, we show evidence that LDD events to empty habitats were strongly prevented during the settlement of Eurasia. This unexpected absence of LDD ahead of the colonization wave front could have been caused by an Allee effect, either due to intrinsic causes such as an inbreeding depression built during the expansion or due to extrinsic causes such as direct competition with archaic humans. Overall, our results suggest only a relatively limited effect of the LGM contraction on current patterns of human diversity. This is in clear contrast with the major role of LDD migrations, which have potentially contributed to the intermingled genetic structure of Eurasian populations.
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Affiliation(s)
- Isabel Alves
- Computational and Molecular Population Genetics Lab, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland Swiss Institute of Bioinformatics, Lausanne, Switzerland Population and Conservation Genetics Group, Instituto Gulbenkian de Ciência, Oeiras, Portugal
| | - Miguel Arenas
- Computational and Molecular Population Genetics Lab, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland Swiss Institute of Bioinformatics, Lausanne, Switzerland Institute of Molecular Pathology and Immunology of the University of Porto (IPATIMUP), Porto, Portugal
| | - Mathias Currat
- Anthropology, Genetics and Peopling History Lab, Department of Genetics & Evolution-Anthropology Unit, University of Geneva, Geneva, Switzerland
| | - Anna Sramkova Hanulova
- Computational and Molecular Population Genetics Lab, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland Swiss Institute of Bioinformatics, Lausanne, Switzerland
| | - Vitor C Sousa
- Computational and Molecular Population Genetics Lab, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland Swiss Institute of Bioinformatics, Lausanne, Switzerland
| | - Nicolas Ray
- EnviroSPACE Lab, Institute for Environmental Sciences, University of Geneva, Geneva, Switzerland
| | - Laurent Excoffier
- Computational and Molecular Population Genetics Lab, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland Swiss Institute of Bioinformatics, Lausanne, Switzerland
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152
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Henry RC, Coulon A, Travis JMJ. Dispersal asymmetries and deleterious mutations influence metapopulation persistence and range dynamics. Evol Ecol 2015. [DOI: 10.1007/s10682-015-9777-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
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153
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Griette Q, Raoul G, Gandon S. Virulence evolution at the front line of spreading epidemics. Evolution 2015; 69:2810-9. [PMID: 26416254 DOI: 10.1111/evo.12781] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2015] [Accepted: 09/14/2015] [Indexed: 01/20/2023]
Abstract
Understanding and predicting the spatial spread of emerging pathogens is a major challenge for the public health management of infectious diseases. Theoretical epidemiology shows that the speed of an epidemic is governed by the life-history characteristics of the pathogen and its ability to disperse. Rapid evolution of these traits during the invasion may thus affect the speed of epidemics. Here we study the influence of virulence evolution on the spatial spread of an epidemic. At the edge of the invasion front, we show that more virulent and transmissible genotypes are expected to win the competition with other pathogens. Behind the front line, however, more prudent exploitation strategies outcompete virulent pathogens. Crucially, even when the presence of the virulent mutant is limited to the edge of the front, the invasion speed can be dramatically altered by pathogen evolution. We support our analysis with individual-based simulations and we discuss the additional effects of demographic stochasticity taking place at the front line on virulence evolution. We confirm that an increase of virulence can occur at the front, but only if the carrying capacity of the invading pathogen is large enough. These results are discussed in the light of recent empirical studies examining virulence evolution at the edge of spreading epidemics.
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Affiliation(s)
- Quentin Griette
- Département de Mathématiques, Faculté des Sciences, Université de Montpellier, Place Eugène Bataillon, Montpellier, France. .,CEFE - UMR 5175, campus CNRS, 1919 route de Mende, 34293 Montpellier, France.
| | - Gaël Raoul
- CEFE - UMR 5175, campus CNRS, 1919 route de Mende, 34293 Montpellier, France.,CMAP - UMR 7641, École Polytechnique, CNRS, Route de Saclay, 91128 Palaiseau Cedex, France
| | - Sylvain Gandon
- CEFE - UMR 5175, campus CNRS, 1919 route de Mende, 34293 Montpellier, France
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154
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Puig M, Castellano D, Pantano L, Giner-Delgado C, Izquierdo D, Gayà-Vidal M, Lucas-Lledó JI, Esko T, Terao C, Matsuda F, Cáceres M. Functional Impact and Evolution of a Novel Human Polymorphic Inversion That Disrupts a Gene and Creates a Fusion Transcript. PLoS Genet 2015; 11:e1005495. [PMID: 26427027 PMCID: PMC4591017 DOI: 10.1371/journal.pgen.1005495] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2014] [Accepted: 08/12/2015] [Indexed: 11/18/2022] Open
Abstract
Despite many years of study into inversions, very little is known about their functional consequences, especially in humans. A common hypothesis is that the selective value of inversions stems in part from their effects on nearby genes, although evidence of this in natural populations is almost nonexistent. Here we present a global analysis of a new 415-kb polymorphic inversion that is among the longest ones found in humans and is the first with clear position effects. This inversion is located in chromosome 19 and has been generated by non-homologous end joining between blocks of transposable elements with low identity. PCR genotyping in 541 individuals from eight different human populations allowed the detection of tag SNPs and inversion genotyping in multiple populations worldwide, showing that the inverted allele is mainly found in East Asia with an average frequency of 4.7%. Interestingly, one of the breakpoints disrupts the transcription factor gene ZNF257, causing a significant reduction in the total expression level of this gene in lymphoblastoid cell lines. RNA-Seq analysis of the effects of this expression change in standard homozygotes and inversion heterozygotes revealed distinct expression patterns that were validated by quantitative RT-PCR. Moreover, we have found a new fusion transcript that is generated exclusively from inverted chromosomes around one of the breakpoints. Finally, by the analysis of the associated nucleotide variation, we have estimated that the inversion was generated ~40,000–50,000 years ago and, while a neutral evolution cannot be ruled out, its current frequencies are more consistent with those expected for a deleterious variant, although no significant association with phenotypic traits has been found so far. Since the discovery of chromosomal inversions almost 100 years ago, how they are maintained in natural populations has been a highly debated issue. One of the hypotheses is that inversion breakpoints could affect genes and modify gene expression levels, although evidence of this came only from laboratory mutants. In humans, a few inversions have been shown to associate with expression differences, but in all cases the molecular causes have remained elusive. Here, we have carried out a complete characterization of a new human polymorphic inversion and determined that it is specific to East Asian populations. In addition, we demonstrate that it disrupts the ZNF257 gene and, through the translocation of the first exon and regulatory sequences, creates a previously nonexistent fusion transcript, which together are associated to expression changes in several other genes. Finally, we investigate the potential evolutionary and phenotypic consequences of the inversion, and suggest that it is probably deleterious. This is therefore the first example of a natural polymorphic inversion that has position effects and creates a new chimeric gene, contributing to answer an old question in evolutionary biology.
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Affiliation(s)
- Marta Puig
- Institut de Biotecnologia i de Biomedicina, Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain
| | - David Castellano
- Institut de Biotecnologia i de Biomedicina, Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain
| | - Lorena Pantano
- Institut de Biotecnologia i de Biomedicina, Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain
| | - Carla Giner-Delgado
- Institut de Biotecnologia i de Biomedicina, Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain
- Departament de Genètica i de Microbiologia, Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain
| | - David Izquierdo
- Institut de Biotecnologia i de Biomedicina, Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain
| | - Magdalena Gayà-Vidal
- Institut de Biotecnologia i de Biomedicina, Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain
| | - José Ignacio Lucas-Lledó
- Institut de Biotecnologia i de Biomedicina, Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain
| | - Tõnu Esko
- Estonian Biobank, Estonian Genome Center, University of Tartu, Tartu, Estonia
- Boston Children's Hospital, Harvard Medical School, and Broad Institute of Harvard and MIT, Boston, Massachusetts, United States of America
| | - Chikashi Terao
- Center for Genomic Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Fumihiko Matsuda
- Center for Genomic Medicine, Kyoto University Graduate School of Medicine, Kyoto, Japan
| | - Mario Cáceres
- Institut de Biotecnologia i de Biomedicina, Universitat Autònoma de Barcelona, Bellaterra, Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
- * E-mail:
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155
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Balick DJ, Do R, Cassa CA, Reich D, Sunyaev SR. Dominance of Deleterious Alleles Controls the Response to a Population Bottleneck. PLoS Genet 2015; 11:e1005436. [PMID: 26317225 PMCID: PMC4552954 DOI: 10.1371/journal.pgen.1005436] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2014] [Accepted: 07/09/2015] [Indexed: 11/30/2022] Open
Abstract
Population bottlenecks followed by re-expansions have been common throughout history of many populations. The response of alleles under selection to such demographic perturbations has been a subject of great interest in population genetics. On the basis of theoretical analysis and computer simulations, we suggest that this response qualitatively depends on dominance. The number of dominant or additive deleterious alleles per haploid genome is expected to be slightly increased following the bottleneck and re-expansion. In contrast, the number of completely or partially recessive alleles should be sharply reduced. Changes of population size expose differences between recessive and additive selection, potentially providing insight into the prevalence of dominance in natural populations. Specifically, we use a simple statistic, BR≡∑xipop1/∑xjpop2, where xi represents the derived allele frequency, to compare the number of mutations in different populations, and detail its functional dependence on the strength of selection and the intensity of the population bottleneck. We also provide empirical evidence showing that gene sets associated with autosomal recessive disease in humans may have a BR indicative of recessive selection. Together, these theoretical predictions and empirical observations show that complex demographic history may facilitate rather than impede inference of parameters of natural selection. Dominance has played a central role in classical genetics since its inception. However, the effect of dominance introduces substantial technical complications into theoretical models describing dynamics of alleles in populations. As a result, dominance is often ignored in population genetic models. Statistical tests for selection built on these models do not discriminate between recessive and additive alleles. We show that historical changes in population size can provide a way to differentiate between recessive and additive selection. Our analysis compares two sub-populations with different demographic histories. History of our own species provides plenty of examples of sub-populations that went through population bottlenecks followed by re-expansions. We show that demographic differences, which generally complicate the analysis, can instead aid in the inference of features of natural selection.
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Affiliation(s)
- Daniel J. Balick
- Division of Genetics, Brigham and Women’s Hospital, Boston, Massachusetts, United States of America
- Department of Medicine, Harvard Medical School, Boston, Massachusetts, United States of America
- Broad Institute of Harvard and MIT, Cambridge, Massachusetts, United States of America
| | - Ron Do
- Broad Institute of Harvard and MIT, Cambridge, Massachusetts, United States of America
- The Charles Bronfman Institute for Personalized Medicine, Icahn School of Medicine at Mount Sinai, New York, New York, United States of America
- The Center for Statistical Genetics, Icahn School of Medicine at Mount Sinai, New York, New York, United States of America
- Department of Genetics and Genomic Sciences, Icahn School of Medicine at Mount Sinai, New York, New York, United States of America
| | - Christopher A. Cassa
- Division of Genetics, Brigham and Women’s Hospital, Boston, Massachusetts, United States of America
- Department of Medicine, Harvard Medical School, Boston, Massachusetts, United States of America
- Broad Institute of Harvard and MIT, Cambridge, Massachusetts, United States of America
| | - David Reich
- Broad Institute of Harvard and MIT, Cambridge, Massachusetts, United States of America
- Howard Hughes Medical Institute, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Shamil R. Sunyaev
- Division of Genetics, Brigham and Women’s Hospital, Boston, Massachusetts, United States of America
- Department of Medicine, Harvard Medical School, Boston, Massachusetts, United States of America
- Broad Institute of Harvard and MIT, Cambridge, Massachusetts, United States of America
- * E-mail:
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156
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Dufresnes C, Perrin N. Effect of biogeographic history on population vulnerability in European amphibians. CONSERVATION BIOLOGY : THE JOURNAL OF THE SOCIETY FOR CONSERVATION BIOLOGY 2015; 29:1235-1241. [PMID: 25833793 DOI: 10.1111/cobi.12490] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2014] [Accepted: 12/23/2014] [Indexed: 06/04/2023]
Abstract
The genetic diversity of populations, which contributes greatly to their adaptive potential, is negatively affected by anthropogenic habitat fragmentation and destruction. However, continental-scale losses of genetic diversity also resulted from the population expansions that followed the end of the last glaciation, an element that is rarely considered in a conservation context. We addressed this issue in a meta-analysis in which we compared the spatial patterns of vulnerability of 18 widespread European amphibians in light of phylogeographic histories (glacial refugia and postglacial routes) and anthropogenic disturbances. Conservation statuses significantly worsened with distances from refugia, particularly in the context of industrial agriculture; human population density also had a negative effect. These findings suggest that features associated with the loss of genetic diversity in post-glacial amphibian populations (such as enhanced fixation load or depressed adaptive potential) may increase their susceptibility to current threats (e.g., habitat fragmentation and pesticide use). We propose that the phylogeographic status of populations (i.e., refugial vs. post-glacial) should be considered in conservation assessments for regional and national red lists.
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Affiliation(s)
- Christophe Dufresnes
- Department of Ecology & Evolution, University of Lausanne, Biophore Building, CH-1015, Lausanne, Switzerland
| | - Nicolas Perrin
- Department of Ecology & Evolution, University of Lausanne, Biophore Building, CH-1015, Lausanne, Switzerland
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157
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Lohmueller KE. The distribution of deleterious genetic variation in human populations. Curr Opin Genet Dev 2015; 29:139-46. [PMID: 25461617 DOI: 10.1016/j.gde.2014.09.005] [Citation(s) in RCA: 86] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Revised: 08/28/2014] [Accepted: 09/05/2014] [Indexed: 11/19/2022]
Abstract
Population genetic studies suggest that most amino-acid changing mutations are deleterious. Such mutations are of tremendous interest in human population genetics as they are important for the evolutionary process and may contribute risk to common disease. Genomic studies over the past 5 years have documented differences across populations in the number of heterozygous deleterious genotypes, number of homozygous derived deleterious genotypes, number of deleterious segregating sites and proportion of sites that are potentially deleterious. These differences have been attributed to population history affecting the ability of natural selection to remove deleterious variants from the population. However, recent studies have suggested that the genetic load is the same across populations and that the efficacy of natural selection has not differed across human populations. Here I show that these observations are not incompatible with each other and that the apparent differences are due to examining different features of the genetic data and differing definitions of terms.
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158
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Daub JT, Dupanloup I, Robinson-Rechavi M, Excoffier L. Inference of Evolutionary Forces Acting on Human Biological Pathways. Genome Biol Evol 2015; 7:1546-58. [PMID: 25971280 PMCID: PMC4494071 DOI: 10.1093/gbe/evv083] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/09/2015] [Indexed: 12/15/2022] Open
Abstract
Because natural selection is likely to act on multiple genes underlying a given phenotypic trait, we study here the potential effect of ongoing and past selection on the genetic diversity of human biological pathways. We first show that genes included in gene sets are generally under stronger selective constraints than other genes and that their evolutionary response is correlated. We then introduce a new procedure to detect selection at the pathway level based on a decomposition of the classical McDonald-Kreitman test extended to multiple genes. This new test, called 2DNS, detects outlier gene sets and takes into account past demographic effects and evolutionary constraints specific to gene sets. Selective forces acting on gene sets can be easily identified by a mere visual inspection of the position of the gene sets relative to their two-dimensional null distribution. We thus find several outlier gene sets that show signals of positive, balancing, or purifying selection but also others showing an ancient relaxation of selective constraints. The principle of the 2DNS test can also be applied to other genomic contrasts. For instance, the comparison of patterns of polymorphisms private to African and non-African populations reveals that most pathways show a higher proportion of nonsynonymous mutations in non-Africans than in Africans, potentially due to different demographic histories and selective pressures.
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Affiliation(s)
- Josephine T Daub
- CMPG, Institute of Ecology and Evolution, University of Berne, Switzerland Swiss Institute of Bioinformatics SIB, Lausanne, Switzerland Present address: Institute of Evolutionary Biology (UPF-CSIC), Barcelona, Spain
| | - Isabelle Dupanloup
- CMPG, Institute of Ecology and Evolution, University of Berne, Switzerland Swiss Institute of Bioinformatics SIB, Lausanne, Switzerland
| | - Marc Robinson-Rechavi
- Swiss Institute of Bioinformatics SIB, Lausanne, Switzerland Department of Ecology and Evolution, University of Lausanne, Switzerland
| | - Laurent Excoffier
- CMPG, Institute of Ecology and Evolution, University of Berne, Switzerland Swiss Institute of Bioinformatics SIB, Lausanne, Switzerland
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159
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Abstract
Next-generation sequencing technology has facilitated the discovery of millions of genetic variants in human genomes. A sizeable fraction of these variants are predicted to be deleterious. Here, we review the pattern of deleterious alleles as ascertained in genome sequencing data sets and ask whether human populations differ in their predicted burden of deleterious alleles - a phenomenon known as mutation load. We discuss three demographic models that are predicted to affect mutation load and relate these models to the evidence (or the lack thereof) for variation in the efficacy of purifying selection in diverse human genomes. We also emphasize why accurate estimation of mutation load depends on assumptions regarding the distribution of dominance and selection coefficients - quantities that remain poorly characterized for current genomic data sets.
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160
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Renaut S, Rieseberg LH. The Accumulation of Deleterious Mutations as a Consequence of Domestication and Improvement in Sunflowers and Other Compositae Crops. Mol Biol Evol 2015; 32:2273-83. [PMID: 25939650 DOI: 10.1093/molbev/msv106] [Citation(s) in RCA: 91] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
For populations to maintain optimal fitness, harmful mutations must be efficiently purged from the genome. Yet, under circumstances that diminish the effectiveness of natural selection, such as the process of plant and animal domestication, deleterious mutations are predicted to accumulate. Here, we compared the load of deleterious mutations in 21 accessions from natural populations and 19 domesticated accessions of the common sunflower using whole-transcriptome single nucleotide polymorphism data. Although we find that genetic diversity has been greatly reduced during domestication, the remaining mutations were disproportionally biased toward nonsynonymous substitutions. Bioinformatically predicted deleterious mutations affecting protein function were especially strongly over-represented. We also identify similar patterns in two other domesticated species of the sunflower family (globe artichoke and cardoon), indicating that this phenomenon is not due to idiosyncrasies of sunflower domestication or the sunflower genome. Finally, we provide unequivocal evidence that deleterious mutations accumulate in low recombining regions of the genome, due to the reduced efficacy of purifying selection. These results represent a conundrum for crop improvement efforts. Although the elimination of harmful mutations should be a long-term goal of plant and animal breeding programs, it will be difficult to weed them out because of limited recombination.
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Affiliation(s)
- Sebastien Renaut
- Biodiversity Research Centre and Department of Botany, University of British Columbia, Vancouver, BC, Canada
| | - Loren H Rieseberg
- Biodiversity Research Centre and Department of Botany, University of British Columbia, Vancouver, BC, Canada Department of Biology, Indiana University - Bloomington
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161
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Peischl S, Excoffier L. Expansion load: recessive mutations and the role of standing genetic variation. Mol Ecol 2015; 24:2084-94. [DOI: 10.1111/mec.13154] [Citation(s) in RCA: 121] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Revised: 03/11/2015] [Accepted: 03/11/2015] [Indexed: 12/13/2022]
Affiliation(s)
- Stephan Peischl
- Institute of Ecology and Evolution; University of Berne; Berne 3012 Switzerland
- Swiss Institute of Bioinformatics; Lausanne 1015 Switzerland
| | - Laurent Excoffier
- Institute of Ecology and Evolution; University of Berne; Berne 3012 Switzerland
- Swiss Institute of Bioinformatics; Lausanne 1015 Switzerland
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162
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Pannell JR. Evolution of the mating system in colonizing plants. Mol Ecol 2015; 24:2018-37. [DOI: 10.1111/mec.13087] [Citation(s) in RCA: 122] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Revised: 01/12/2015] [Accepted: 01/15/2015] [Indexed: 12/16/2022]
Affiliation(s)
- John R. Pannell
- Department of Ecology and Evolution; University of Lausanne; Biophore Building 1015 Lausanne Switzerland
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163
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164
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Bock DG, Caseys C, Cousens RD, Hahn MA, Heredia SM, Hübner S, Turner KG, Whitney KD, Rieseberg LH. What we still don't know about invasion genetics. Mol Ecol 2015; 24:2277-97. [PMID: 25474505 DOI: 10.1111/mec.13032] [Citation(s) in RCA: 235] [Impact Index Per Article: 26.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2014] [Revised: 11/27/2014] [Accepted: 11/28/2014] [Indexed: 12/12/2022]
Abstract
Publication of The Genetics of Colonizing Species in 1965 launched the field of invasion genetics and highlighted the value of biological invasions as natural ecological and evolutionary experiments. Here, we review the past 50 years of invasion genetics to assess what we have learned and what we still don't know, focusing on the genetic changes associated with invasive lineages and the evolutionary processes driving these changes. We also suggest potential studies to address still-unanswered questions. We now know, for example, that rapid adaptation of invaders is common and generally not limited by genetic variation. On the other hand, and contrary to prevailing opinion 50 years ago, the balance of evidence indicates that population bottlenecks and genetic drift typically have negative effects on invasion success, despite their potential to increase additive genetic variation and the frequency of peak shifts. Numerous unknowns remain, such as the sources of genetic variation, the role of so-called expansion load and the relative importance of propagule pressure vs. genetic diversity for successful establishment. While many such unknowns can be resolved by genomic studies, other questions may require manipulative experiments in model organisms. Such studies complement classical reciprocal transplant and field-based selection experiments, which are needed to link trait variation with components of fitness and population growth rates. We conclude by discussing the potential for studies of invasion genetics to reveal the limits to evolution and to stimulate the development of practical strategies to either minimize or maximize evolutionary responses to environmental change.
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Affiliation(s)
- Dan G Bock
- Department of Botany and Biodiversity Research Centre, University of British Columbia, Room 3529-6270 University Blvd, Vancouver, BC, V6T 1Z4, Canada
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165
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Hodgins KA, Bock DG, Hahn MA, Heredia SM, Turner KG, Rieseberg LH. Comparative genomics in the Asteraceae reveals little evidence for parallel evolutionary change in invasive taxa. Mol Ecol 2015; 24:2226-40. [PMID: 25439241 DOI: 10.1111/mec.13026] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2014] [Revised: 11/23/2014] [Accepted: 11/26/2014] [Indexed: 01/12/2023]
Abstract
Asteraceae, the largest family of flowering plants, has given rise to many notorious invasive species. Using publicly available transcriptome assemblies from 35 Asteraceae, including six major invasive species, we examined evidence for micro- and macro-evolutionary genomic changes associated with invasion. To detect episodes of positive selection repeated across multiple introductions, we conducted comparisons between native and introduced genotypes from six focal species and identified genes with elevated rates of amino acid change (dN/dS). We then looked for evidence of positive selection at a broader phylogenetic scale across all taxa. As invasive species may experience founder events during colonization and spread, we also looked for evidence of increased genetic load in introduced genotypes. We rarely found evidence for parallel changes in orthologous genes in the intraspecific comparisons, but in some cases we identified changes in members of the same gene family. Using among-species comparisons, we detected positive selection in 0.003-0.69% and 2.4-7.8% of the genes using site and stochastic branch-site models, respectively. These genes had diverse putative functions, including defence response, stress response and herbicide resistance, although there was no clear pattern in the GO terms. There was no indication that introduced genotypes have a higher proportion of deleterious alleles than native genotypes in the six focal species, suggesting multiple introductions and admixture mitigated the impact of drift. Our findings provide little evidence for common genomic responses in invasive taxa of the Asteraceae and hence suggest that multiple evolutionary pathways may lead to adaptation during introduction and spread in these species.
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Affiliation(s)
- Kathryn A Hodgins
- School of Biological Sciences, Monash University, Clayton, Vic., 3800, Australia
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166
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Evolutionary genetic bases of longevity and senescence. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2015; 847:1-44. [PMID: 25916584 DOI: 10.1007/978-1-4939-2404-2_1] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Senescence, as a time-dependent developmental process, affects all organisms at every stage in their development and growth. During this process, genetic, epigenetic and environmental factors are known to introduce a wide range of variation for longevity among individuals. As an important life-history trait, longevity shows ontogenetic relationships with other complex traits, and hence may be viewed as a composite trait. Factors that influence the origin and maintenance of diversity of life are ultimately governed by Darwinian processes. Here we review evolutionary genetic mechanisms underlying longevity and senescence in humans from a life-history and genotype-epigenetic-phenotype (G-E-P) map prospective. We suggest that synergistic and cascading effects of cis-ruptive mechanisms in the genome, and epigenetic disruptive processes in relation to environmental factors may lead to sequential slippage in the G-E-P space. These mechanisms accompany age, stage and individual specific senescent processes, influenced by positive pleiotropy of certain genes, superior genome integrity, negative-frequency dependent selection and other factors that universally regulate rarity in nature. Finally we interpret life span as an inherent property of self-organizing systems that, accordingly, maintain species-specific limits for the entire complex of fitness traits. We conclude that Darwinian approaches provide unique opportunities to discover the biological bases of longevity as well as devise individual specific medical or other interventions toward improving health span.
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167
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Fu W, Gittelman R, Bamshad M, Akey J. Characteristics of neutral and deleterious protein-coding variation among individuals and populations. Am J Hum Genet 2014; 95:421-36. [PMID: 25279984 DOI: 10.1016/j.ajhg.2014.09.006] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2014] [Accepted: 09/11/2014] [Indexed: 01/27/2023] Open
Abstract
Whole-genome and exome data sets continue to be produced at a frenetic pace, resulting in massively large catalogs of human genomic variation. However, a clear picture of the characteristics and patterns of neutral and deleterious variation within and between populations has yet to emerge, given that recent large-scale sequencing studies have often emphasized different aspects of the data and sometimes appear to have conflicting conclusions. Here, we comprehensively studied characteristics of protein-coding variation in high-coverage exome sequence data from 6,515 European American (EA) and African American (AA) individuals. We developed an unbiased approach to identify putatively deleterious variants and investigated patterns of neutral and deleterious single-nucleotide variants and alleles between individuals and populations. We show that there are substantial differences in the composition of genotypes between EA and AA populations and that small but statistically significant differences exist in the average number of deleterious alleles carried by EA and AA individuals. Furthermore, we performed extensive simulations to delineate the temporal dynamics of deleterious alleles for a broad range of demographic models and use these data to inform the interpretation of empirical patterns of deleterious variation. Finally, we illustrate that the effects of demographic perturbations, such as bottlenecks and expansions, often manifest in opposing patterns of neutral and deleterious variation depending on whether the focus is on populations or individuals. Our results clarify seemingly disparate empirical characteristics of protein-coding variation and provide substantial insights into how natural selection and demographic history have patterned neutral and deleterious variation within and between populations.
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168
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Abstract
Competition between independently arising beneficial mutations is enhanced in spatial populations due to the linear rather than exponential growth of clones. Recent theoretical studies have pointed out that the resulting fitness dynamics is analogous to a surface growth process, where new layers nucleate and spread stochastically, leading to the build up of scale-invariant roughness. This scenario differs qualitatively from the standard view of adaptation in that the speed of adaptation becomes independent of population size while the fitness variance does not. Here we exploit recent progress in the understanding of surface growth processes to obtain precise predictions for the universal, non-Gaussian shape of the fitness distribution for one-dimensional habitats, which are verified by simulations. When the mutations are deleterious rather than beneficial the problem becomes a spatial version of Muller's ratchet. In contrast to the case of well-mixed populations, the rate of fitness decline remains finite even in the limit of an infinite habitat, provided the ratio [Formula: see text] between the deleterious mutation rate and the square of the (negative) selection coefficient is sufficiently large. Using, again, an analogy to surface growth models we show that the transition between the stationary and the moving state of the ratchet is governed by directed percolation.
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Affiliation(s)
- Jakub Otwinowski
- Emory University, Physics Department Atlanta, Georgia, USA. University of Pennsylvania, Biology Department, Philadelphia, Pennsylvania, USA
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169
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Impact of range expansions on current human genomic diversity. Curr Opin Genet Dev 2014; 29:22-30. [PMID: 25156518 DOI: 10.1016/j.gde.2014.07.007] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2014] [Revised: 07/09/2014] [Accepted: 07/25/2014] [Indexed: 12/19/2022]
Abstract
The patterns of population genetic diversity depend to a large extent on past demographic history. Most human populations are known to have gone recently through a series of range expansions within and out of Africa, but these spatial expansions are rarely taken into account when interpreting observed genomic diversity, possibly because they are difficult to model. Here we review available evidence in favour of range expansions out of Africa, and we discuss several of their consequences on neutral and selected diversity, including some recent observations on an excess of rare neutral and selected variants in large samples. We further show that in spatially subdivided populations, the sampling strategy can severely impact the resulting genetic diversity and be confounded by past demography. We conclude that ignoring the spatial structure of human population can lead to some misinterpretations of extant genetic diversity.
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170
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Thinking outside the barrier: neutral and adaptive divergence in Indo-Pacific coral reef faunas. Evol Ecol 2014. [DOI: 10.1007/s10682-014-9724-9] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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171
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Hoban S. An overview of the utility of population simulation software in molecular ecology. Mol Ecol 2014; 23:2383-401. [DOI: 10.1111/mec.12741] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2013] [Revised: 03/22/2014] [Accepted: 03/26/2014] [Indexed: 01/12/2023]
Affiliation(s)
- Sean Hoban
- National Institute for Mathematical and Biological Synthesis; University of Tennessee; 1122 Volunteer Blvd. Suite 110A Knoxville TN 37996-3410 USA
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172
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Flaxman SM. Surfing downhill: when should population range expansion be characterized by reductions in fitness? Mol Ecol 2014; 22:5963-5. [PMID: 24138111 DOI: 10.1111/mec.12564] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2013] [Revised: 10/11/2013] [Accepted: 10/13/2013] [Indexed: 11/29/2022]
Abstract
Deleterious mutations are found in all populations. Their existence at low frequencies is easily understood, but explaining how they reach high frequencies has long been a challenging problem for population geneticists and evolutionary biologists. Some cases of apparently deleterious alleles are explained by pleiotropy or environmental context dependence, but for universally deleterious alleles, two mechanisms are generally invoked to explain how they can reach high frequencies: (i) genetic drift in small populations and (ii) 'hitchhiking' (sensu Maynard Smith J, Haigh J, Genetical Research, 1974, 23, 23-35) involving tight linkage to beneficial mutations. However, these oft-cited explanations do not immediately resolve the problem because many real populations of interest have population sizes and recombination rates that are large enough to render it nearly impossible for all but the most weakly deleterious (i.e. nearly neutral) mutations to establish and persist. Furthermore, both mechanisms are usually silent about patterns of intraspecific variation in mutation load. In this issue, Peischl S, Dupanloup I, Kirkpatrick M, Excoffier L (Molecular Ecology, 2013) develop and explore a mechanism that puts drift and hitchhiking of deleterious mutations into a specific spatial and demographic context: range expansions. Importantly, their findings provide a plausible explanation for puzzling empirical patterns, such as the paradoxical observation that genotypes at the leading edge of a range expansion are sometimes less fit than those in the ancestral range (when fitness is assessed in a common environment).
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Affiliation(s)
- Samuel M Flaxman
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80309, USA
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173
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Wegmann D, Currat M. Recipient of the 2013 Molecular Ecology Prize: Laurent Excoffier. Mol Ecol 2013; 23:16-9. [PMID: 24283664 DOI: 10.1111/mec.12604] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2013] [Accepted: 11/25/2013] [Indexed: 11/28/2022]
Affiliation(s)
- Daniel Wegmann
- Department of Biology, University of Fribourg, 1700, Fribourg, Switzerland
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