151
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Ortiz‐Barrientos D, James ME. Evolution of recombination rates and the genomic landscape of speciation. J Evol Biol 2017; 30:1519-1521. [DOI: 10.1111/jeb.13116] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2017] [Revised: 05/07/2017] [Accepted: 05/08/2017] [Indexed: 01/02/2023]
Affiliation(s)
- D. Ortiz‐Barrientos
- School of Biological Sciences The University of Queensland St Lucia Qld Australia
| | - M. E. James
- School of Biological Sciences The University of Queensland St Lucia Qld Australia
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152
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Christie JR, Beekman M. Uniparental Inheritance Promotes Adaptive Evolution in Cytoplasmic Genomes. Mol Biol Evol 2017; 34:677-691. [PMID: 28025277 PMCID: PMC5896580 DOI: 10.1093/molbev/msw266] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Eukaryotes carry numerous asexual cytoplasmic genomes (mitochondria and plastids). Lacking recombination, asexual genomes should theoretically suffer from impaired adaptive evolution. Yet, empirical evidence indicates that cytoplasmic genomes experience higher levels of adaptive evolution than predicted by theory. In this study, we use a computational model to show that the unique biology of cytoplasmic genomes-specifically their organization into host cells and their uniparental (maternal) inheritance-enable them to undergo effective adaptive evolution. Uniparental inheritance of cytoplasmic genomes decreases competition between different beneficial substitutions (clonal interference), promoting the accumulation of beneficial substitutions. Uniparental inheritance also facilitates selection against deleterious cytoplasmic substitutions, slowing Muller's ratchet. In addition, uniparental inheritance generally reduces genetic hitchhiking of deleterious substitutions during selective sweeps. Overall, uniparental inheritance promotes adaptive evolution by increasing the level of beneficial substitutions relative to deleterious substitutions. When we assume that cytoplasmic genome inheritance is biparental, decreasing the number of genomes transmitted during gametogenesis (bottleneck) aids adaptive evolution. Nevertheless, adaptive evolution is always more efficient when inheritance is uniparental. Our findings explain empirical observations that cytoplasmic genomes-despite their asexual mode of reproduction-can readily undergo adaptive evolution.
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Affiliation(s)
- Joshua R Christie
- School of Life and Environmental Sciences, The University of Sydney, Sydney, NSW, Australia
| | - Madeleine Beekman
- School of Life and Environmental Sciences, The University of Sydney, Sydney, NSW, Australia
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153
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Chu HY, Sprouffske K, Wagner A. The role of recombination in evolutionary adaptation of Escherichia coli to a novel nutrient. J Evol Biol 2017; 30:1692-1711. [PMID: 28612351 DOI: 10.1111/jeb.13132] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2017] [Revised: 05/11/2017] [Accepted: 06/05/2017] [Indexed: 12/11/2022]
Abstract
The benefits and detriments of recombination for adaptive evolution have been studied both theoretically and experimentally, with conflicting predictions and observations. Most pertinent experiments examine recombination's effects in an unchanging environment and do not study its genomewide effects. Here, we evolved six replicate populations of either highly recombining R+ or lowly recombining R- E. coli strains in a changing environment, by introducing the novel nutrients L-arabinose or indole into the environment. The experiment's ancestral strains are not viable on these nutrients, but 130 generations of adaptive evolution were sufficient to render them viable. Recombination conferred a more pronounced advantage to populations adapting to indole. To study the genomic changes associated with this advantage, we sequenced the genomes of 384 clones isolated from selected replicates at the end of the experiment. These genomes harbour complex changes that range from point mutations to large-scale DNA amplifications. Among several candidate adaptive mutations, those in the tryptophanase regulator tnaC stand out, because the tna operon in which it resides has a known role in indole metabolism. One of the highly recombining populations also shows a significant excess of large-scale segmental DNA amplifications that include the tna operon. This lineage also shows a unique and potentially adaptive combination of point mutations and DNA amplifications that may have originated independently from one another, to be joined later by recombination. Our data illustrate that the advantages of recombination for adaptive evolution strongly depend on the environment and that they can be associated with complex genomic changes.
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Affiliation(s)
- H-Y Chu
- Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland
| | - K Sprouffske
- Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland
| | - A Wagner
- Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland.,The Swiss Institute of Bioinformatics, Quartier Sorge, Batiment Genopode, Lausanne, Switzerland.,The Santa Fe Institute, Santa Fe, NM, USA
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154
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Structural Variation Shapes the Landscape of Recombination in Mouse. Genetics 2017; 206:603-619. [PMID: 28592499 DOI: 10.1534/genetics.116.197988] [Citation(s) in RCA: 44] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Accepted: 03/13/2017] [Indexed: 01/02/2023] Open
Abstract
Meiotic recombination is an essential feature of sexual reproduction that ensures faithful segregation of chromosomes and redistributes genetic variants in populations. Multiparent populations such as the Diversity Outbred (DO) mouse stock accumulate large numbers of crossover (CO) events between founder haplotypes, and thus present a unique opportunity to study the role of genetic variation in shaping the recombination landscape. We obtained high-density genotype data from [Formula: see text] DO mice, and localized 2.2 million CO events to intervals with a median size of 28 kb. The resulting sex-averaged genetic map of the DO population is highly concordant with large-scale (order 10 Mb) features of previously reported genetic maps for mouse. To examine fine-scale (order 10 kb) patterns of recombination in the DO, we overlaid putative recombination hotspots onto our CO intervals. We found that CO intervals are enriched in hotspots compared to the genomic background. However, as many as [Formula: see text] of CO intervals do not overlap any putative hotspots, suggesting that our understanding of hotspots is incomplete. We also identified coldspots encompassing 329 Mb, or [Formula: see text] of observable genome, in which there is little or no recombination. In contrast to hotspots, which are a few kilobases in size, and widely scattered throughout the genome, coldspots have a median size of 2.1 Mb and are spatially clustered. Coldspots are strongly associated with copy-number variant (CNV) regions, especially multi-allelic clusters, identified from whole-genome sequencing of 228 DO mice. Genes in these regions have reduced expression, and epigenetic features of closed chromatin in male germ cells, which suggests that CNVs may repress recombination by altering chromatin structure in meiosis. Our findings demonstrate how multiparent populations, by bridging the gap between large-scale and fine-scale genetic mapping, can reveal new features of the recombination landscape.
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155
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Short Rotations in Forest Plantations Accelerate Virulence Evolution in Root-Rot Pathogenic Fungi. FORESTS 2017. [DOI: 10.3390/f8060205] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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156
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Baker Z, Schumer M, Haba Y, Bashkirova L, Holland C, Rosenthal GG, Przeworski M. Repeated losses of PRDM9-directed recombination despite the conservation of PRDM9 across vertebrates. eLife 2017; 6:e24133. [PMID: 28590247 PMCID: PMC5519329 DOI: 10.7554/elife.24133] [Citation(s) in RCA: 86] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2016] [Accepted: 06/03/2017] [Indexed: 01/01/2023] Open
Abstract
Studies of highly diverged species have revealed two mechanisms by which meiotic recombination is directed to the genome-through PRDM9 binding or by targeting promoter-like features-that lead to dramatically different evolutionary dynamics of hotspots. Here, we identify PRDM9 orthologs from genome and transcriptome data in 225 species. We find the complete PRDM9 ortholog across distantly related vertebrates but, despite this broad conservation, infer a minimum of six partial and three complete losses. Strikingly, taxa carrying the complete ortholog of PRDM9 are precisely those with rapid evolution of its predicted binding affinity, suggesting that all domains are necessary for directing recombination. Indeed, as we show, swordtail fish carrying only a partial but conserved ortholog share recombination properties with PRDM9 knock-outs.
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Affiliation(s)
- Zachary Baker
- Department of Systems Biology, Columbia University, New York City, United States
| | - Molly Schumer
- Department of Biological Sciences, Columbia University, New York City, United States
- Harvard Society of Fellows, Harvard University, Cambridge, United States
- Centro de Investigaciones Científicas de las Huastecas 'Aguazarca', Hidalgo, Mexico
| | - Yuki Haba
- Department of Evolution, Ecology and Environmental Biology, Columbia University, New York City, United States
| | - Lisa Bashkirova
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York City, United States
| | - Chris Holland
- Centro de Investigaciones Científicas de las Huastecas 'Aguazarca', Hidalgo, Mexico
- Department of Biology, Texas A&M University, College Station, United States
| | - Gil G Rosenthal
- Centro de Investigaciones Científicas de las Huastecas 'Aguazarca', Hidalgo, Mexico
- Department of Biology, Texas A&M University, College Station, United States
| | - Molly Przeworski
- Department of Systems Biology, Columbia University, New York City, United States
- Department of Biological Sciences, Columbia University, New York City, United States
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157
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Sex initiates adaptive evolution by recombination between beneficial loci. PLoS One 2017; 12:e0177895. [PMID: 28575015 PMCID: PMC5456038 DOI: 10.1371/journal.pone.0177895] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2016] [Accepted: 05/04/2017] [Indexed: 11/19/2022] Open
Abstract
Current theory proposes that sex can increase genetic variation and produce high fitness genotypes if genetic associations between alleles at different loci are non-random. In case beneficial and deleterious alleles at different loci are in linkage disequilibrium, sex may i) recombine beneficial alleles of different loci, ii) liberate beneficial alleles from genetic backgrounds of low fitness, or iii) recombine deleterious mutations for more effective elimination. In our study, we found that the first mechanism dominated the initial phase of adaptive evolution in Brachionus calyciflorus rotifers during a natural selection experiment. We used populations that had been locally adapted to two environments previously, creating a linkage disequilibrium between beneficial and deleterious alleles at different loci in a combined environment. We observed the highest fitness increase when several beneficial alleles of different loci could be recombined, while the other mechanisms were ineffective. Our study thus provides evidence for the hypothesis that sex can speed up adaptation by recombination between beneficial alleles of different loci, in particular during early stages of adaptive evolution in our system. We also suggest that the benefits of sex might change over time and state of adaptive progress.
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158
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Lagator M, Paixão T, Barton NH, Bollback JP, Guet CC. On the mechanistic nature of epistasis in a canonical cis-regulatory element. eLife 2017; 6. [PMID: 28518057 PMCID: PMC5481185 DOI: 10.7554/elife.25192] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Accepted: 05/17/2017] [Indexed: 01/02/2023] Open
Abstract
Understanding the relation between genotype and phenotype remains a major challenge. The difficulty of predicting individual mutation effects, and particularly the interactions between them, has prevented the development of a comprehensive theory that links genotypic changes to their phenotypic effects. We show that a general thermodynamic framework for gene regulation, based on a biophysical understanding of protein-DNA binding, accurately predicts the sign of epistasis in a canonical cis-regulatory element consisting of overlapping RNA polymerase and repressor binding sites. Sign and magnitude of individual mutation effects are sufficient to predict the sign of epistasis and its environmental dependence. Thus, the thermodynamic model offers the correct null prediction for epistasis between mutations across DNA-binding sites. Our results indicate that a predictive theory for the effects of cis-regulatory mutations is possible from first principles, as long as the essential molecular mechanisms and the constraints these impose on a biological system are accounted for. DOI:http://dx.doi.org/10.7554/eLife.25192.001 Mutations are changes to DNA that provide the raw material upon which evolution can act. Therefore, to understand evolution, we need to know the effects of mutations, and how those mutations interact with each other (a phenomenon referred to as epistasis). So far, few mathematical models allow scientists to predict the effects of mutations, and even fewer are able to predict epistasis. Biological systems are complex and consist of many proteins and other molecules. Genes are the sections of DNA that provide the instructions needed to produce these molecules, and some genes encode proteins that can bind to DNA to control whether other genes are switched on or off. Lagator, Paixão et al. have now used mathematical models and experiments to understand how the environment inside the cells of a bacterium known as E. coli, specifically the amount of particular proteins, affects epistasis. These mathematical models are able to predict interactions between mutations in the most abundant class of DNA-binding sites in proteins. This approach found that the nature of the interaction between mutations can be explained through biophysical laws, combined with the basic knowledge of the logic of how genes regulate each other’s activities. Furthermore, the models allow Lagator, Paixão et al. to predict interactions between mutations in several different environments, such as the presence of a new food source or a toxin, defined by the amounts of relevant DNA-binding proteins in cells. By providing new ways of understanding how genes are regulated in bacteria, and how gene regulation is affected by mutations, these findings contribute to our understanding of how organisms evolve. In addition, this work may help us to build artificial networks of genes that interact with each other to produce a desired response, such as more efficient production of fuel from ethanol or the break down of hazardous chemicals. DOI:http://dx.doi.org/10.7554/eLife.25192.002
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Affiliation(s)
- Mato Lagator
- Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - Tiago Paixão
- Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - Nicholas H Barton
- Institute of Science and Technology Austria, Klosterneuburg, Austria
| | - Jonathan P Bollback
- Institute of Science and Technology Austria, Klosterneuburg, Austria.,Department of Integrative Biology, University of Liverpool, Liverpool, United Kingdom
| | - Călin C Guet
- Institute of Science and Technology Austria, Klosterneuburg, Austria
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159
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Hartmann FE, Sánchez-Vallet A, McDonald BA, Croll D. A fungal wheat pathogen evolved host specialization by extensive chromosomal rearrangements. THE ISME JOURNAL 2017; 11:1189-1204. [PMID: 28117833 PMCID: PMC5437930 DOI: 10.1038/ismej.2016.196] [Citation(s) in RCA: 98] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Revised: 10/10/2016] [Accepted: 11/25/2016] [Indexed: 11/09/2022]
Abstract
Fungal pathogens can rapidly evolve virulence towards resistant crops in agricultural ecosystems. Gains in virulence are often mediated by the mutation or deletion of a gene encoding a protein recognized by the plant immune system. However, the loci and the mechanisms of genome evolution enabling rapid virulence evolution are poorly understood. We performed genome-wide association mapping on a global collection of 106 strains of Zymoseptoria tritici, the most damaging pathogen of wheat in Europe, to identify polymorphisms linked to virulence on two wheat varieties. We found 25 distinct genomic loci associated with reproductive success of the pathogen. However, no locus was shared between the host genotypes, suggesting host specialization. The main locus associated with virulence encoded a highly expressed, small secreted protein. Population genomic analyses showed that the gain in virulence was explained by a segregating gene deletion polymorphism. The deletion was likely adaptive by preventing detection of the encoded protein. Comparative genomics of closely related species showed that the locus emerged de novo since speciation. A large cluster of transposable elements in direct proximity to the locus generated extensive rearrangements leading to multiple independent gene losses. Our study demonstrates that rapid turnover in the chromosomal structure of a pathogen can drive host specialization.
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Affiliation(s)
- Fanny E Hartmann
- Plant Pathology, Institute of Integrative Biology, Zurich, Switzerland
| | | | - Bruce A McDonald
- Plant Pathology, Institute of Integrative Biology, Zurich, Switzerland
| | - Daniel Croll
- Plant Pathology, Institute of Integrative Biology, Zurich, Switzerland
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160
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Variation in Recombination Rate: Adaptive or Not? Trends Genet 2017; 33:364-374. [DOI: 10.1016/j.tig.2017.03.003] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 03/06/2017] [Accepted: 03/07/2017] [Indexed: 01/30/2023]
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161
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Smith SRT, Connallon T. The contribution of the mitochondrial genome to sex‐specific fitness variance. Evolution 2017; 71:1417-1424. [DOI: 10.1111/evo.13238] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2017] [Revised: 03/13/2017] [Accepted: 03/17/2017] [Indexed: 12/14/2022]
Affiliation(s)
- Shane R. T. Smith
- School of Biological Sciences Monash University Clayton VIC 3800 Australia
| | - Tim Connallon
- School of Biological Sciences Monash University Clayton VIC 3800 Australia
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162
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Wilburn DB, Doty KA, Chouinard AJ, Eddy SL, Woodley SK, Houck LD, Feldhoff RC. Olfactory effects of a hypervariable multicomponent pheromone in the red-legged salamander, Plethodon shermani. PLoS One 2017; 12:e0174370. [PMID: 28358844 PMCID: PMC5373537 DOI: 10.1371/journal.pone.0174370] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Accepted: 03/06/2017] [Indexed: 11/18/2022] Open
Abstract
Chemical communication via chemosensory signaling is an essential process for promoting and modifying reproductive behavior in many species. During courtship in plethodontid salamanders, males deliver a mixture of non-volatile proteinaceous pheromones that activate chemosensory neurons in the vomeronasal epithelium (VNE) and increase female receptivity. One component of this mixture, Plethodontid Modulating Factor (PMF), is a hypervariable pheromone expressed as more than 30 unique isoforms that differ between individual males-likely driven by co-evolution with female receptors to promote gene duplication and positive selection of the PMF gene complex. Courtship trials with females receiving different PMF isoform mixtures had variable effects on female mating receptivity, with only the most complex mixtures increasing receptivity, such that we believe that sufficient isoform diversity allows males to improve their reproductive success with any female in the mating population. The aim of this study was to test the effects of isoform variability on VNE neuron activation using the agmatine uptake assay. All isoform mixtures activated a similar number of neurons (>200% over background) except for a single purified PMF isoform (+17%). These data further support the hypothesis that PMF isoforms act synergistically in order to regulate female receptivity, and different putative mechanisms are discussed.
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Affiliation(s)
- Damien B. Wilburn
- Dept of Biochemistry and Molecular Biology, University of Louisville, Louisville, Kentucky, United States of America
- Dept of Genome Sciences, University of Washington, Seattle, Washington, United States of America
- * E-mail:
| | - Kari A. Doty
- Dept of Biochemistry and Molecular Biology, University of Louisville, Louisville, Kentucky, United States of America
| | - Adam J. Chouinard
- Dept of Zoology, Oregon State University, Corvallis, Oregon, United States of America
| | - Sarah L. Eddy
- Dept of Zoology, Oregon State University, Corvallis, Oregon, United States of America
| | - Sarah K. Woodley
- Dept of Biological Sciences, Duquesne University, Pittsburgh, Pennsylvania, United States of America
| | - Lynne D. Houck
- Dept of Zoology, Oregon State University, Corvallis, Oregon, United States of America
| | - Richard C. Feldhoff
- Dept of Biochemistry and Molecular Biology, University of Louisville, Louisville, Kentucky, United States of America
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163
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Gélin P, Fauvelot C, Mehn V, Bureau S, Rouzé H, Magalon H. Superclone Expansion, Long-Distance Clonal Dispersal and Local Genetic Structuring in the Coral Pocillopora damicornis Type β in Reunion Island, South Western Indian Ocean. PLoS One 2017; 12:e0169692. [PMID: 28068406 PMCID: PMC5222339 DOI: 10.1371/journal.pone.0169692] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Accepted: 12/19/2016] [Indexed: 11/18/2022] Open
Abstract
The scleractinian coral Pocillopora damicornis type β is known to present a mixed reproduction mode: through sexual reproduction, new genotypes are created, while asexual reproduction insures their propagation. In order to investigate the relative proportion of each reproduction mode in P. damicornis type β populations from Reunion Island, Indian Ocean, clonal propagation along the west coast was assessed through four sampling sites with increasing geographical distance between sites. Coral colonies were sampled either exhaustively, randomly or haphazardly within each site, and genotypic diversity was assessed using 13 microsatellite loci over a total of 510 P. damicornis type β determined a posteriori from their mtDNA haplotype (a 840 bp sequenced fragment of the Open Reading Frame). Overall, 47% of all the sampled colonies presented the same multi-locus genotype (MLG), a superclone, suggesting that asexual propagation is extremely important in Reunion Island. Within each site, numerous MLGs were shared by several colonies, suggesting local clonal propagation through fragmentation. Moreover, some of these MLGs were found to be shared among several sites located 40 km apart. While asexual reproduction by fragmentation seems unlikely over long distances, our results suggest a production of parthenogenetic larvae. Despite shared MLGs, two differentiated clusters were enclosed among populations of the west coast of Reunion Island, revealing the necessity to set up appropriate managing strategies at a local scale.
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Affiliation(s)
- Pauline Gélin
- UMR ENTROPIE (IRD, Université de La Réunion, CNRS), Laboratoire d’excellence-CORAIL, Université de La Réunion, St Denis, La Réunion
- * E-mail:
| | - Cécile Fauvelot
- UMR ENTROPIE (IRD, Université de La Réunion, CNRS), Laboratoire d’excellence-CORAIL, centre IRD de Nouméa, New Caledonia
| | - Vincent Mehn
- UMR ENTROPIE (IRD, Université de La Réunion, CNRS), Laboratoire d’excellence-CORAIL, Université de La Réunion, St Denis, La Réunion
| | - Sophie Bureau
- UMR ENTROPIE (IRD, Université de La Réunion, CNRS), Laboratoire d’excellence-CORAIL, Université de La Réunion, St Denis, La Réunion
| | - Héloïse Rouzé
- UMR ENTROPIE (IRD, Université de La Réunion, CNRS), Laboratoire d’excellence-CORAIL, centre IRD de Nouméa, New Caledonia
| | - Hélène Magalon
- UMR ENTROPIE (IRD, Université de La Réunion, CNRS), Laboratoire d’excellence-CORAIL, Université de La Réunion, St Denis, La Réunion
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164
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Wang RJ, Gray MM, Parmenter MD, Broman KW, Payseur BA. Recombination rate variation in mice from an isolated island. Mol Ecol 2016; 26:457-470. [PMID: 27864900 DOI: 10.1111/mec.13932] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Revised: 11/09/2016] [Accepted: 11/14/2016] [Indexed: 01/14/2023]
Abstract
Recombination rate is a heritable trait that varies among individuals. Despite the major impact of recombination rate on patterns of genetic diversity and the efficacy of selection, natural variation in this phenotype remains poorly characterized. We present a comparison of genetic maps, sampling 1212 meioses, from a unique population of wild house mice (Mus musculus domesticus) that recently colonized remote Gough Island. Crosses to a mainland reference strain (WSB/EiJ) reveal pervasive variation in recombination rate among Gough Island mice, including subchromosomal intervals spanning up to 28% of the genome. In spite of this high level of polymorphism, the genomewide recombination rate does not significantly vary. In general, we find that recombination rate varies more when measured in smaller genomic intervals. Using the current standard genetic map of the laboratory mouse to polarize intervals with divergent recombination rates, we infer that the majority of evolutionary change occurred in one of the two tested lines of Gough Island mice. Our results confirm that natural populations harbour a high level of recombination rate polymorphism and highlight the disparities in recombination rate evolution across genomic scales.
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Affiliation(s)
- Richard J Wang
- Laboratory of Genetics, University of Wisconsin - Madison, 425-G Henry Mall, 2428 Genetics, Madison, WI, 53706, USA
| | - Melissa M Gray
- Laboratory of Genetics, University of Wisconsin - Madison, 425-G Henry Mall, 2428 Genetics, Madison, WI, 53706, USA
| | - Michelle D Parmenter
- Laboratory of Genetics, University of Wisconsin - Madison, 425-G Henry Mall, 2428 Genetics, Madison, WI, 53706, USA
| | - Karl W Broman
- Department of Biostatistics & Medical Informatics, University of Wisconsin - Madison, Madison, WI, 53706, USA
| | - Bret A Payseur
- Laboratory of Genetics, University of Wisconsin - Madison, 425-G Henry Mall, 2428 Genetics, Madison, WI, 53706, USA
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165
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Cooper JD, Kerr B. Evolution at 'Sutures' and 'Centers': Recombination Can Aid Adaptation of Spatially Structured Populations on Rugged Fitness Landscapes. PLoS Comput Biol 2016; 12:e1005247. [PMID: 27973606 PMCID: PMC5156365 DOI: 10.1371/journal.pcbi.1005247] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Accepted: 11/14/2016] [Indexed: 01/14/2023] Open
Abstract
Epistatic interactions among genes can give rise to rugged fitness landscapes, in which multiple “peaks” of high-fitness allele combinations are separated by “valleys” of low-fitness genotypes. How populations traverse rugged fitness landscapes is a long-standing question in evolutionary biology. Sexual reproduction may affect how a population moves within a rugged fitness landscape. Sex may generate new high-fitness genotypes by recombination, but it may also destroy high-fitness genotypes by shuffling the genes of a fit parent with a genetically distinct mate, creating low-fitness offspring. Either of these opposing aspects of sex require genotypic diversity in the population. Spatially structured populations may harbor more diversity than well-mixed populations, potentially amplifying both positive and negative effects of sex. On the other hand, spatial structure leads to clumping in which mating is more likely to occur between like types, diminishing the effects of recombination. In this study, we use computer simulations to investigate the combined effects of recombination and spatial structure on adaptation in rugged fitness landscapes. We find that spatially restricted mating and offspring dispersal may allow multiple genotypes inhabiting suboptimal peaks to coexist, and recombination at the “sutures” between the clusters of these genotypes can create genetically novel offspring. Sometimes such an offspring genotype inhabits a new peak on the fitness landscape. In such a case, spatially restricted mating allows this fledgling subpopulation to avoid recombination with distinct genotypes, as mates are more likely to be the same genotype. Such population “centers” can allow nascent peaks to establish despite recombination. Spatial structure may therefore allow an evolving population to enjoy the creative side of sexual recombination while avoiding its destructive side. For a novel genotype to establish in a population, it must (1) be created, and (2) not be subsequently lost. Recombination is a double-edged sword in this process, potentially fostering creation, but also hastening loss as the novel genotype is being recombined with other genotypes, especially when rare. In this study, we find that spatial structure may affect both the creative and destructive aspects of recombination in rugged fitness landscapes. By slowing the spread of high-fitness genotypes, spatially restricted mating and dispersal may allow diverse subpopulations to arise. Reproduction across the borders of these subpopulations—at “sutures”—may create genetic novelty. Depending on the topography of the fitness landscape, such novelty may be in the domain of attraction of a new, higher peak; the population may “peak-jump” to an area of genotype space unlikely to be explored by mutation alone. Lineages founded by peak-jumping events are particularly prone to early extinction, as recombination with unlike genotypes may disrupt the rare allele combination and thereby produce low-fitness offspring. However, these fledgling peak lineages may be protected from early extinction by mating within small homotypic clusters—in “centers”. Thus, spatial structure may allow a population to create rare genotypes via recombination, and allow those rare genotypes to persist despite recombination.
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Affiliation(s)
- Jacob D. Cooper
- Department of Biology, University of Washington, Seattle, Washington, United States of America
- BEACON Center for the Study of Evolution in Action, University of Washington, Seattle, Washington, United States of America
- * E-mail:
| | - Benjamin Kerr
- Department of Biology, University of Washington, Seattle, Washington, United States of America
- BEACON Center for the Study of Evolution in Action, University of Washington, Seattle, Washington, United States of America
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166
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Huang BH, Chen YW, Huang CL, Gao J, Liao PC. Imbalanced positive selection maintains the functional divergence of duplicated DIHYDROKAEMPFEROL 4-REDUCTASE genes. Sci Rep 2016; 6:39031. [PMID: 27966614 PMCID: PMC5155217 DOI: 10.1038/srep39031] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Accepted: 11/16/2016] [Indexed: 01/19/2023] Open
Abstract
Gene duplication could be beneficial by functional division but might increase the risk of genetic load. The dynamics of duplicated paralogs number could involve recombination, positive selection, and functional divergence. Duplication of DIHYDROFLAVONOL 4-REDUCTASE (DFR) has been reported in several organisms and may have been retained by escape from adaptive conflict (EAC). In this study, we screened the angiosperm DFR gene focusing on a diversified genus Scutellaria to investigate how these duplicated genes are retained. We deduced that gene duplication involved multiple independent events in angiosperms, but the duplication of DFR was before the divergence of Scutellaria. Asymmetric positive selective pressures resulted in different evolutionary rates between the duplicates. Different numbers of regulatory elements, differential codon usages, radical amino acid changes, and differential gene expressions provide evidences of functional divergence between the two DFR duplicates in Scutellaria, implying adaptive subfunctionalization between duplicates. The discovery of pseudogenes accompanying a reduced replacement rate in one DFR paralogous gene suggested possibly leading to “loss of function” due to dosage imbalance after the transient adaptive subfunctionalization in the early stage of duplication. Notwithstanding, episodic gene duplication and functional divergence may be relevant to the diversification of ecological function of DFR gene in Scutellaria.
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Affiliation(s)
- Bing-Hong Huang
- Department of Life Science, National Taiwan Normal University, Taipei 11677, Taiwan
| | - Yi-Wen Chen
- Department of Biological Science and Technology, National Pingtung University of Science and Technology, Pingtung 91201, Taiwan
| | - Chia-Lung Huang
- Department of Life Science, National Taiwan Normal University, Taipei 11677, Taiwan
| | - Jian Gao
- The Key Laboratory for Silviculture and Conservation of Ministry of Education, College of Forestry, Beijing Forestry University, Beijing 100083, China
| | - Pei-Chun Liao
- Department of Life Science, National Taiwan Normal University, Taipei 11677, Taiwan
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167
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Abstract
Fungal plant pathogens rapidly evolve virulence on resistant hosts through mutations in genes encoding proteins that modulate the host immune responses. The mutational spectrum likely includes chromosomal rearrangements responsible for gains or losses of entire genes. However, the mechanisms creating adaptive structural variation in fungal pathogen populations are poorly understood. We used complete genome assemblies to quantify structural variants segregating in the highly polymorphic fungal wheat pathogen Zymoseptoria tritici The genetic basis of virulence in Z. tritici is complex, and populations harbor significant genetic variation for virulence; hence, we aimed to identify whether structural variation led to functional differences. We combined single-molecule real-time sequencing, genetic maps, and transcriptomics data to generate a fully assembled and annotated genome of the highly virulent field isolate 3D7. Comparative genomics analyses against the complete reference genome IPO323 identified large chromosomal inversions and the complete gain or loss of transposable-element clusters, explaining the extensive chromosomal-length polymorphisms found in this species. Both the 3D7 and IPO323 genomes harbored long tracts of sequences exclusive to one of the two genomes. These orphan regions contained 296 genes unique to the 3D7 genome and not previously known for this species. These orphan genes tended to be organized in clusters and showed evidence of mutational decay. Moreover, the orphan genes were enriched in genes encoding putative effectors and included a gene that is one of the most upregulated putative effector genes during wheat infection. Our study showed that this pathogen species harbored extensive chromosomal structure polymorphism that may drive the evolution of virulence. IMPORTANCE Pathogen outbreak populations often harbor previously unknown genes conferring virulence. Hence, a key puzzle of rapid pathogen evolution is the origin of such evolutionary novelty in genomes. Chromosomal rearrangements and structural variation in pathogen populations likely play a key role. However, identifying such polymorphism is challenging, as most genome-sequencing approaches only yield information about point mutations. We combined long-read technology and genetic maps to assemble the complete genome of a strain of a highly polymorphic fungal pathogen of wheat. Comparisons against the reference genome of the species showed substantial variation in the chromosome structure and revealed large regions unique to each assembled genome. These regions were enriched in genes encoding likely effector proteins, which are important components of pathogenicity. Our study showed that pathogen populations harbor extensive polymorphism at the chromosome level and that this polymorphism can be a source of adaptive genetic variation in pathogen evolution.
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168
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Macaya-Sanz D, Heuertz M, Lindtke D, Vendramin GG, Lexer C, González-Martínez SC. Causes and consequences of large clonal assemblies in a poplar hybrid zone. Mol Ecol 2016; 25:5330-5344. [PMID: 27661461 DOI: 10.1111/mec.13850] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2015] [Revised: 09/02/2016] [Accepted: 09/06/2016] [Indexed: 11/27/2022]
Abstract
Asexual reproduction is a common and fundamental mode of reproduction in plants. Although persistence in adverse conditions underlies most known cases of clonal dominance, proximal genetic drivers remain unclear, in particular for populations dominated by a few large clones. In this study, we studied a clonal population of the riparian tree Populus alba in the Douro river basin (northwestern Iberian Peninsula) where it hybridizes with Populus tremula, a species that grows in highly contrasted ecological conditions. We used 73 nuclear microsatellites to test whether genomic background (species ancestry) is a relevant cause of clonal success, and to assess the evolutionary consequences of clonal dominance by a few genets. Additional genotyping-by-sequencing data were produced to estimate the age of the largest clones. We found that a few ancient (over a few thousand years old) and widespread genets dominate the population, both in terms of clone size and number of sexual offspring produced. Interestingly, large clones possessed two genomic regions introgressed from P. tremula, which may have favoured their spread under stressful environmental conditions. At the population level, the spread of large genets was accompanied by an overall ancient (>0.1 Myr) but soft decline of effective population size. Despite this decrease, and the high clonality and dominance of sexual reproduction by large clones, the Douro hybrid zone still displays considerable genetic diversity and low inbreeding. This suggests that even in extreme cases as in the Douro, asexual and sexual dominance of a few large, geographically extended individuals does not threaten population survival.
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Affiliation(s)
- David Macaya-Sanz
- Department of Forest Ecology and Genetics, INIA-Forest Research Centre, Madrid, 28040, Spain.,Department of Biology, West Virginia University, Morgantown, WV, 26505, USA
| | | | - Dorothea Lindtke
- Unit of Ecology and Evolution, Department of Biology, University of Fribourg, Fribourg, 1700, Switzerland.,Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK
| | - Giovanni G Vendramin
- Institute of Biosciences and Bioresources, National Research Council, Sesto Fiorentino (Florence), 50019, Italy
| | - Christian Lexer
- Unit of Ecology and Evolution, Department of Biology, University of Fribourg, Fribourg, 1700, Switzerland.,Department of Botany and Biodiversity Research, Faculty of Life Sciences, University of Vienna, Vienna, A-1030, Austria
| | - Santiago C González-Martínez
- Department of Forest Ecology and Genetics, INIA-Forest Research Centre, Madrid, 28040, Spain. .,BIOGECO, INRA, Univ. Bordeaux, Cestas, 33610, France.
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169
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Hosseini SR, Martin OC, Wagner A. Phenotypic innovation through recombination in genome-scale metabolic networks. Proc Biol Sci 2016; 283:rspb.2016.1536. [PMID: 27683361 DOI: 10.1098/rspb.2016.1536] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Accepted: 09/06/2016] [Indexed: 12/17/2022] Open
Abstract
Recombination is an important source of metabolic innovation, especially in prokaryotes, which have evolved the ability to survive on many different sources of chemical elements and energy. Metabolic systems have a well-understood genotype-phenotype relationship, which permits a quantitative and biochemically principled understanding of how recombination creates novel phenotypes. Here, we investigate the power of recombination to create genome-scale metabolic reaction networks that enable an organism to survive in new chemical environments. To this end, we use flux balance analysis, an experimentally validated computational method that can predict metabolic phenotypes from metabolic genotypes. We show that recombination is much more likely to create novel metabolic abilities than random changes in chemical reactions of a metabolic network. We also find that phenotypic innovation is more likely when recombination occurs between parents that are genetically closely related, phenotypically highly diverse, and viable on few rather than many carbon sources. Survival on a new carbon source preferentially involves reactions that are superessential, that is, essential in many metabolic networks. We validate our observations with data from 61 reconstructed prokaryotic metabolic networks. Our systematic and quantitative analysis of metabolic systems helps understand how recombination creates innovation.
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Affiliation(s)
- Sayed-Rzgar Hosseini
- Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Building Y27, Winterthurerstrasse 190, 8057 Zurich, Switzerland The Swiss Institute of Bioinformatics, Quartier Sorge, Batiment Genopode, 1015 Lausanne, Switzerland
| | - Olivier C Martin
- GQE-Le Moulon, INRA, Université Paris-Sud, CNRS, AgroParisTech, Université Paris-Saclay, 91190 Gif-sur-Yvette, France
| | - Andreas Wagner
- Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Building Y27, Winterthurerstrasse 190, 8057 Zurich, Switzerland The Swiss Institute of Bioinformatics, Quartier Sorge, Batiment Genopode, 1015 Lausanne, Switzerland The Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, NM 87501, USA
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170
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The Fitness Effects of Spontaneous Mutations Nearly Unseen by Selection in a Bacterium with Multiple Chromosomes. Genetics 2016; 204:1225-1238. [PMID: 27672096 DOI: 10.1534/genetics.116.193060] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2016] [Accepted: 09/06/2016] [Indexed: 12/18/2022] Open
Abstract
Mutation accumulation (MA) experiments employ the strategy of minimizing the population size of evolving lineages to greatly reduce effects of selection on newly arising mutations. Thus, most mutations fix within MA lines independently of their fitness effects. This approach, more recently combined with genome sequencing, has detailed the rates, spectra, and biases of different mutational processes. However, a quantitative understanding of the fitness effects of mutations virtually unseen by selection has remained an untapped opportunity. Here, we analyzed the fitness of 43 sequenced MA lines of the multi-chromosome bacterium Burkholderia cenocepacia that had each undergone 5554 generations of MA and accumulated an average of 6.73 spontaneous mutations. Most lineages exhibited either neutral or deleterious fitness in three different environments in comparison with their common ancestor. The only mutational class that was significantly overrepresented in lineages with reduced fitness was the loss of the plasmid, though nonsense mutations, missense mutations, and coding insertion-deletions were also overrepresented in MA lineages whose fitness had significantly declined. Although the overall distribution of fitness effects was similar between the three environments, the magnitude and even the sign of the fitness of a number of lineages changed with the environment, demonstrating that the fitness of some genotypes was environmentally dependent. These results present an unprecedented picture of the fitness effects of spontaneous mutations in a bacterium with multiple chromosomes and provide greater quantitative support for the theory that the vast majority of spontaneous mutations are neutral or deleterious.
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171
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Ahlawat S, Sharma P, Sharma R, Arora R, Verma NK, Brahma B, Mishra P, De S. Evidence of positive selection and concerted evolution in the rapidly evolving PRDM9 zinc finger domain in goats and sheep. Anim Genet 2016; 47:740-751. [PMID: 27621101 DOI: 10.1111/age.12487] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/05/2016] [Indexed: 01/20/2023]
Abstract
Meiotic recombination contributes to augmentation of genetic diversity, exclusion of deleterious alleles and proper segregation of chromatids. PRDM9 has been identified as the gene responsible for specifying the location of recombination hotspots during meiosis and is also the only known vertebrate gene associated with reproductive isolation between species. PRDM9 encodes a protein with a highly variable zinc finger (ZF) domain that varies between as well as within species. In the present study, the ZF domain of PRDM9 on chromosome 1 was characterized for the first time in 15 goat breeds and 25 sheep breeds of India. A remarkable variation in the number and sequence of ZF domains was observed. The number of ZF repeats in the ZF array varied from eight to 12 yielding five homozygous and 10 heterozygous genotypes. The number of different ZF domains was 84 and 52 producing 36 and 26 unique alleles in goats and sheep respectively. The posterior mean of dN/dS or omega values were calculated using the codeml tool of pamlx to identify amino acids that are evolving positively in goats and sheep, as positions -1, +3 and +6 in the ZF domain have been reported to experience strong positive selection across different lineages. Our study identified sites -5, -1, +3, +4 and +6 to be experiencing positive selection. Small ruminant zinc fingers were also found to be evolving under concerted evolution. Our results demonstrate the existence of a vast diversity of PRDM9 in goats and sheep, which is in concert with reports in many metazoans.
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Affiliation(s)
- S Ahlawat
- National Bureau of Animal Genetic Resources, Karnal 132001, Haryana, India.
| | - P Sharma
- National Bureau of Animal Genetic Resources, Karnal 132001, Haryana, India
| | - R Sharma
- National Bureau of Animal Genetic Resources, Karnal 132001, Haryana, India
| | - R Arora
- National Bureau of Animal Genetic Resources, Karnal 132001, Haryana, India
| | - N K Verma
- National Bureau of Animal Genetic Resources, Karnal 132001, Haryana, India
| | - B Brahma
- National Dairy Research Institute, Karnal 132001, Haryana, India
| | - P Mishra
- National Dairy Research Institute, Karnal 132001, Haryana, India
| | - S De
- National Dairy Research Institute, Karnal 132001, Haryana, India
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172
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Frank SA. Puzzles in modern biology. II. Language, cancer and the recursive processes of evolutionary innovation. F1000Res 2016; 5:2289. [PMID: 28184282 PMCID: PMC5288677 DOI: 10.12688/f1000research.9568.1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 09/06/2016] [Indexed: 11/20/2022] Open
Abstract
Human language emerged abruptly. Diverse body forms evolved suddenly. Seed-bearing plants spread rapidly. How do complex evolutionary innovations arise so quickly? Resolving alternative claims remains difficult. The great events of the past happened a long time ago. Cancer provides a model to study evolutionary innovation. A tumor must evolve many novel traits to become an aggressive cancer. I use what we know or could study about cancer to describe the key processes of innovation. In general, evolutionary systems form a hierarchy of recursive processes. Those recursive processes determine the rates at which innovations are generated, spread and transmitted. I relate the recursive processes to abrupt evolutionary innovation.
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Affiliation(s)
- Steven A. Frank
- Department of Ecology and Evolutionary Biology, University of California, Irvine, Irvine, CA, 92697–2525, USA
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173
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Abstract
Mutation generates a steady supply of genetic variation that, while occasionally useful for adaptation, is more often deleterious for fitness. Recent research has emphasized that the fitness effects of mutations often differ between the sexes, leading to important evolutionary consequences for the maintenance of genetic variation and long-term population viability. Some forms of sex-specific selection-i.e., stronger purifying selection in males than females-can help purge a population's load of female-harming mutations and promote population growth. Other scenarios-e.g., sexually antagonistic selection, in which mutations that harm females are beneficial for males-inflate genetic loads and potentially dampen population viability. Evolutionary processes of sexual antagonism and purifying selection are likely to impact the evolutionary dynamics of different loci within a genome, yet theory has mostly ignored the potential for interactions between such loci to jointly shape the evolutionary genetic basis of female and male fitness variation. Here, we show that sexually antagonistic selection at a locus tends to elevate the frequencies of deleterious alleles at tightly linked loci that evolve under purifying selection. Moreover, haplotypes that segregate for different sexually antagonistic alleles accumulate different types of deleterious mutations. Haplotypes that carry female-benefit sexually antagonistic alleles preferentially accumulate mutations that are primarily male harming, whereas male-benefit haplotypes accumulate mutations that are primarily female harming. The theory predicts that sexually antagonistic selection should shape the genomic organization of genetic variation that differentially impacts female and male fitness, and contribute to sexual dimorphism in the genetic basis of fitness variation.
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174
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Radzvilavicius AL, Blackstone NW. Conflict and cooperation in eukaryogenesis: implications for the timing of endosymbiosis and the evolution of sex. J R Soc Interface 2016; 12:20150584. [PMID: 26468067 DOI: 10.1098/rsif.2015.0584] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Roughly 1.5-2.0 Gya, the eukaryotic cell evolved from an endosymbiosis of an archaeal host and proteobacterial symbionts. The timing of this endosymbiosis relative to the evolution of eukaryotic features remains subject to considerable debate, yet the evolutionary process itself constrains the timing of these events. Endosymbiosis entailed levels-of-selection conflicts, and mechanisms of conflict mediation had to evolve for eukaryogenesis to proceed. The initial mechanisms of conflict mediation (e.g. signalling with calcium and soluble adenylyl cyclase, substrate carriers, adenine nucleotide translocase, uncouplers) led to metabolic homeostasis in the eukaryotic cell. Later mechanisms (e.g. mitochondrial gene loss) contributed to the chimeric eukaryotic genome. These integral features of eukaryotes were derived because of, and therefore subsequent to, endosymbiosis. Perhaps the greatest opportunity for conflict arose with the emergence of eukaryotic sex, involving whole-cell fusion. A simple model demonstrates that competition on the lower level severely hinders the evolution of sex. Cytoplasmic mixing, however, is beneficial for non-cooperative endosymbionts, which could have used their aerobic metabolism to manipulate the life history of the host. While early evolution of sex may have facilitated symbiont acquisition, sex would have also destabilized the subsequent endosymbiosis. More plausibly, the evolution of sex and the true nucleus concluded the transition.
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Affiliation(s)
- Arunas L Radzvilavicius
- Department of Genetics, Evolution and Environment and CoMPLEX, University College London, Gower Street, London WC1E 6BT, UK
| | - Neil W Blackstone
- Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115
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175
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Fisher KJ, Lang GI. Experimental evolution in fungi: An untapped resource. Fungal Genet Biol 2016; 94:88-94. [PMID: 27375178 DOI: 10.1016/j.fgb.2016.06.007] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Revised: 06/28/2016] [Accepted: 06/30/2016] [Indexed: 10/21/2022]
Abstract
Historically, evolutionary biology has been considered an observational science. Examining populations and inferring evolutionary histories mold evolutionary theories. In contrast, laboratory evolution experiments make use of the amenability of traditional model organisms to study fundamental processes underlying evolution in real time in simple, but well-controlled, environments. With advances in high-throughput biology and next generation sequencing, it is now possible to propagate hundreds of parallel populations over thousands of generations and to quantify precisely the frequencies of various mutations over time. Experimental evolution combines the ability to simultaneously monitor replicate populations with the power to vary individual parameters to test specific evolutionary hypotheses, something that is impractical or infeasible in natural populations. Many labs are now conducting laboratory evolution experiments in nearly all model systems including viruses, bacteria, yeast, nematodes, and fruit flies. Among these systems, fungi occupy a unique niche: with a short generation time, small compact genomes, and sexual cycles, fungi are a particularly valuable and largely untapped resource for propelling future growth in the field of experimental evolution. Here, we describe the current state of fungal experimental evolution and why fungi are uniquely positioned to answer many of the outstanding questions in the field. We also review which fungal species are most well suited for experimental evolution.
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Affiliation(s)
- Kaitlin J Fisher
- Department of Biological Sciences, Lehigh University, Bethlehem, PA 18015, USA.
| | - Gregory I Lang
- Department of Biological Sciences, Lehigh University, Bethlehem, PA 18015, USA.
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176
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Tabata J, Ichiki RT, Tanaka H, Kageyama D. Sexual versus Asexual Reproduction: Distinct Outcomes in Relative Abundance of Parthenogenetic Mealybugs following Recent Colonization. PLoS One 2016; 11:e0156587. [PMID: 27322381 PMCID: PMC4920589 DOI: 10.1371/journal.pone.0156587] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2016] [Accepted: 05/17/2016] [Indexed: 01/17/2023] Open
Abstract
Asexual reproduction, including parthenogenesis in which embryos develop within a female without fertilization, is assumed to confer advantages over sexual reproduction, which includes a “cost of males.” Sexual reproduction largely predominates in animals, however, indicating that this cost is outweighed by the genetic and/or ecological benefits of sexuality, including the acquisition of advantageous mutations occurring in different individuals and the elimination of deleterious mutations. But the evolution of sexual reproduction remains unclear, because we have limited examples that demonstrate the relative success of sexual lineages in the face of competition from asexual lineages in the same environment. Here we investigated a sympatric occurrence of sexual and asexual reproduction in the pineapple mealybug, Dysmicoccus brevipes. This pest invaded southwestern Japan, including Okinawa and Ishigaki Islands, in the 1930s in association with imported pineapple plants. Our recent censuses demonstrated that on Okinawa sexually reproducing individuals can coexist with and even dominate asexual individuals in the presence of habitat and resource competition, which is considered to be severe for this nearly immobile insect. Molecular phylogeny based on partial DNA sequences in the mitochondrial and nuclear genomes, as well as the endosymbiotic bacterial genome, revealed that the asexual lineage diverged from a common sexual ancestor in the relatively recent past. In contrast, only the asexual lineage exhibiting obligate apomictic thelytoky was discovered on Ishigaki. Co-existence of the two lineages cannot be explained by the results of laboratory experiments, which showed that the intrinsic rate of increase in the sexual lineage was not obviously superior to that of the asexual lineage. Differences in biotic and/or abiotic selective forces operating on the two islands might be the cause of this discrepancy. This biological system offers a unique opportunity to assess the relative success of sexual versus asexual lineages with an unusual morphology and life cycle.
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Affiliation(s)
- Jun Tabata
- National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba, Ibaraki 305–8604, Japan
- * E-mail:
| | - Ryoko T. Ichiki
- Japan International Research Center for Agricultural Sciences, 1–1 Ohwashi, Tsukuba, Ibaraki 305–8686, Japan
| | - Hirotaka Tanaka
- Tottori Prefectural Museum, 2–124 Higashi-machi, Tottori, Tottori 680–0011, Japan
| | - Daisuke Kageyama
- National Institute of Agrobiological Sciences, 1–2 Ohwashi, Tsukuba, Ibaraki 305–8634, Japan
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177
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Stieha C, García-Ramos G, Nicholas McLetchie D, Crowley P. Maintenance of the sexes and persistence of a clonal organism in spatially complex metapopulations. Evol Ecol 2016. [DOI: 10.1007/s10682-016-9841-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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178
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Sharp NP, Otto SP. Evolution of sex: Using experimental genomics to select among competing theories. Bioessays 2016; 38:751-7. [DOI: 10.1002/bies.201600074] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
| | - Sarah P. Otto
- Department of Zoology; University of British Columbia; Vancouver Canada
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179
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Markov AV, Kaznacheev IS. Evolutionary consequences of polyploidy in prokaryotes and the origin of mitosis and meiosis. Biol Direct 2016; 11:28. [PMID: 27277956 PMCID: PMC4898445 DOI: 10.1186/s13062-016-0131-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Accepted: 06/03/2016] [Indexed: 02/08/2023] Open
Abstract
Background The origin of eukaryote-specific traits such as mitosis and sexual reproduction remains disputable. There is growing evidence that both mitosis and eukaryotic sex (i.e., the alternation of syngamy and meiosis) may have already existed in the basal eukaryotes. The mating system of the halophilic archaeon Haloferax volcanii probably represents an intermediate stage between typical prokaryotic and eukaryotic sex. H. volcanii is highly polyploid, as well as many other Archaea. Here, we use computer simulation to explore genetic and evolutionary outcomes of polyploidy in amitotic prokaryotes and its possible role in the origin of mitosis, meiosis and eukaryotic sex. Results Modeling suggests that polyploidy can confer strong short-term evolutionary advantage to amitotic prokaryotes. However, it also promotes the accumulation of recessive deleterious mutations and the risk of extinction in the long term, especially in highly mutagenic environment. There are several possible strategies that amitotic polyploids can use in order to reduce the genetic costs of polyploidy while retaining its benefits. Interestingly, most of these strategies resemble different components or aspects of eukaryotic sex. They include asexual ploidy cycles, equalization of genome copies by gene conversion, high-frequency lateral gene transfer between relatives, chromosome exchange coupled with homologous recombination, and the evolution of more accurate chromosome distribution during cell division (mitosis). Acquisition of mitosis by an amitotic polyploid results in chromosome diversification and specialization. Ultimately, it transforms a polyploid cell into a functionally monoploid one with multiple unique, highly redundant chromosomes. Specialization of chromosomes makes the previously evolved modes of promiscuous chromosome shuffling deleterious. This can result in selective pressure to develop accurate mechanisms of homolog pairing, and, ultimately, meiosis. Conclusion Emergence of mitosis and the first evolutionary steps towards eukaryotic sex could have taken place in the ancestral polyploid, amitotic proto-eukaryotes, as they were struggling to survive in the highly mutagenic environment of the Early Proterozoic shallow water microbial communities, through the succession of the following stages: (1) acquisition of high-frequency between-individual genetic exchange coupled with homologous recombination; (2) acquisition of mitosis, followed by rapid chromosome diversification and specialization; (3) evolution of homolog synapsis and meiosis. Additional evidence compatible with this scenario includes mass acquisition of new families of paralogous genes by the basal eukaryotes, and recently discovered correlation between polyploidy and the presence of histones in Archaea. Reviewer This article was reviewed by Eugene Koonin, Uri Gophna and Armen Mulkidjanian. For the full reviews, please go to the Reviewers' comments section.
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Affiliation(s)
- Alexander V Markov
- Biological Faculty, Department of Biological Evolution, M.V. Lomonosov Moscow State University, Leninskie Gory, 1, Bldg. 12, Moscow, 119991, Russia.
| | - Ilya S Kaznacheev
- Biological Faculty, Department of Biological Evolution, M.V. Lomonosov Moscow State University, Leninskie Gory, 1, Bldg. 12, Moscow, 119991, Russia
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180
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Rafajlović M, Emanuelsson A, Johannesson K, Butlin RK, Mehlig B. A universal mechanism generating clusters of differentiated loci during divergence-with-migration. Evolution 2016; 70:1609-21. [PMID: 27196373 PMCID: PMC5089645 DOI: 10.1111/evo.12957] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2016] [Revised: 05/04/2016] [Accepted: 05/06/2016] [Indexed: 02/02/2023]
Abstract
Genome‐wide patterns of genetic divergence reveal mechanisms of adaptation under gene flow. Empirical data show that divergence is mostly concentrated in narrow genomic regions. This pattern may arise because differentiated loci protect nearby mutations from gene flow, but recent theory suggests this mechanism is insufficient to explain the emergence of concentrated differentiation during biologically realistic timescales. Critically, earlier theory neglects an inevitable consequence of genetic drift: stochastic loss of local genomic divergence. Here, we demonstrate that the rate of stochastic loss of weak local differentiation increases with recombination distance to a strongly diverged locus and, above a critical recombination distance, local loss is faster than local “gain” of new differentiation. Under high migration and weak selection, this critical recombination distance is much smaller than the total recombination distance of the genomic region under selection. Consequently, divergence between populations increases by net gain of new differentiation within the critical recombination distance, resulting in tightly linked clusters of divergence. The mechanism responsible is the balance between stochastic loss and gain of weak local differentiation, a mechanism acting universally throughout the genome. Our results will help to explain empirical observations and lead to novel predictions regarding changes in genomic architectures during adaptive divergence.
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Affiliation(s)
- Marina Rafajlović
- Department of Physics, University of Gothenburg, SE-412 96, Gothenburg, Sweden. .,The Linnaeus Centre for Marine Evolutionary Biology, University of Gothenburg, SE-405 30, Gothenburg, Sweden.
| | - Anna Emanuelsson
- Department of Physics, University of Gothenburg, SE-412 96, Gothenburg, Sweden
| | - Kerstin Johannesson
- The Linnaeus Centre for Marine Evolutionary Biology, University of Gothenburg, SE-405 30, Gothenburg, Sweden.,Department of Marine Sciences-Tjärnö, University of Gothenburg, SE-452 96, Strömstad, Sweden
| | - Roger K Butlin
- The Linnaeus Centre for Marine Evolutionary Biology, University of Gothenburg, SE-405 30, Gothenburg, Sweden.,Department of Animal and Plant Sciences, University of Sheffield, Sheffield S10 2TN, United Kingdom
| | - Bernhard Mehlig
- Department of Physics, University of Gothenburg, SE-412 96, Gothenburg, Sweden.,The Linnaeus Centre for Marine Evolutionary Biology, University of Gothenburg, SE-405 30, Gothenburg, Sweden
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181
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Van Cleve J. Cooperation, conformity, and the coevolutionary problem of trait associations. J Theor Biol 2016; 396:13-24. [PMID: 26907203 DOI: 10.1016/j.jtbi.2016.02.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Revised: 01/24/2016] [Accepted: 02/10/2016] [Indexed: 11/29/2022]
Abstract
In large scale social systems, coordinated or cooperative outcomes become difficult because encounters between kin or repeated encounters between friends are infrequent. Even punishment of noncooperators does not entirely alleviate the dilemma. One important mechanism for achieving cooperative outcomes in such social systems is conformist bias where individuals copy the behavior performed by the majority of their group mates. Conformist bias enhances group competition by both stabilizing behaviors within groups and increasing variance between groups. Due to this group competition effect, conformist bias is thought to have been an important driver of human social complexity and cultural diversity. However, conformist bias only evolves indirectly through associations with other traits, and I show that such associations are more difficult to obtain than previously expected. Specifically, I show that initial measures of population structure must be strong in order for a strong association between conformist bias and cooperative behaviors (cooperation and costly punishment) to evolve and for these traits to reach high frequencies. Additionally, the required initial level of association does not evolve de novo in simulations run over long timescales. This suggests that the coevolution of cooperative behaviors and conformist bias alone may not explain the high levels of cooperation within human groups, though conformist bias may still play an important role in combination with other social and demographic forces.
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Affiliation(s)
- Jeremy Van Cleve
- Department of Biology, University of Kentucky, Lexington, KY 40506, USA.
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182
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An Evolving Genetic Architecture Interacts with Hill-Robertson Interference to Determine the Benefit of Sex. Genetics 2016; 203:923-36. [PMID: 27098911 DOI: 10.1534/genetics.116.186916] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2016] [Accepted: 04/06/2016] [Indexed: 02/05/2023] Open
Abstract
Sex is ubiquitous in the natural world, but the nature of its benefits remains controversial. Previous studies have suggested that a major advantage of sex is its ability to eliminate interference between selection on linked mutations, a phenomenon known as Hill-Robertson interference. However, those studies may have missed both important advantages and important disadvantages of sexual reproduction because they did not allow the distributions of mutational effects and interactions (i.e., the genetic architecture) to evolve. Here we investigate how Hill-Robertson interference interacts with an evolving genetic architecture to affect the evolutionary origin and maintenance of sex by simulating evolution in populations of artificial gene networks. We observed a long-term advantage of sex-equilibrium mean fitness of sexual populations exceeded that of asexual populations-that did not depend on population size. We also observed a short-term advantage of sex-sexual modifier mutations readily invaded asexual populations-that increased with population size, as was observed in previous studies. We show that the long- and short-term advantages of sex were both determined by differences between sexual and asexual populations in the evolutionary dynamics of two properties of the genetic architecture: the deleterious mutation rate ([Formula: see text]) and recombination load ([Formula: see text]). These differences resulted from a combination of selection to minimize [Formula: see text] which is experienced only by sexuals, and Hill-Robertson interference experienced primarily by asexuals. In contrast to the previous studies, in which Hill-Robertson interference had only a direct impact on the fitness advantages of sex, the impact of Hill-Robertson interference in our simulations was mediated additionally by an indirect impact on the efficiency with which selection acted to reduce [Formula: see text].
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183
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Conserved Genetic Architecture Underlying Individual Recombination Rate Variation in a Wild Population of Soay Sheep (Ovis aries). Genetics 2016; 203:583-98. [PMID: 27029733 PMCID: PMC4858801 DOI: 10.1534/genetics.115.185553] [Citation(s) in RCA: 94] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Accepted: 03/11/2016] [Indexed: 02/06/2023] Open
Abstract
Meiotic recombination breaks down linkage disequilibrium (LD) and forms new haplotypes, meaning that it is an important driver of diversity in eukaryotic genomes. Understanding the causes of variation in recombination rate is important in interpreting and predicting evolutionary phenomena and in understanding the potential of a population to respond to selection. However, despite attention in model systems, there remains little data on how recombination rate varies at the individual level in natural populations. Here we used extensive pedigree and high-density SNP information in a wild population of Soay sheep (Ovis aries) to investigate the genetic architecture of individual autosomal recombination rates. Individual rates were high relative to other mammal systems and were higher in males than in females (autosomal map lengths of 3748 and 2860 cM, respectively). The heritability of autosomal recombination rate was low but significant in both sexes (h2 = 0.16 and 0.12 in females and males, respectively). In females, 46.7% of the heritable variation was explained by a subtelomeric region on chromosome 6; a genome-wide association study showed the strongest associations at locus RNF212, with further associations observed at a nearby ∼374-kb region of complete LD containing three additional candidate loci, CPLX1, GAK, and PCGF3. A second region on chromosome 7 containing REC8 and RNF212B explained 26.2% of the heritable variation in recombination rate in both sexes. Comparative analyses with 40 other sheep breeds showed that haplotypes associated with recombination rates are both old and globally distributed. Both regions have been implicated in rate variation in mice, cattle, and humans, suggesting a common genetic architecture of recombination rate variation in mammals.
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184
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Nagaraja P, Alexander HK, Bonhoeffer S, Dixit NM. Influence of recombination on acquisition and reversion of immune escape and compensatory mutations in HIV-1. Epidemics 2016; 14:11-25. [DOI: 10.1016/j.epidem.2015.09.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Revised: 09/11/2015] [Accepted: 09/11/2015] [Indexed: 11/28/2022] Open
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185
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Fontcuberta García-Cuenca A, Dumas Z, Schwander T. Extreme genetic diversity in asexual grass thrips populations. J Evol Biol 2016; 29:887-99. [PMID: 26864612 DOI: 10.1111/jeb.12843] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Accepted: 02/03/2016] [Indexed: 12/01/2022]
Abstract
The continuous generation of genetic variation has been proposed as one of the main factors explaining the maintenance of sexual reproduction in nature. However, populations of asexual individuals may attain high levels of genetic diversity through within-lineage diversification, replicate transitions to asexuality from sexual ancestors and migration. How these mechanisms affect genetic variation in populations of closely related sexual and asexual taxa can therefore provide insights into the role of genetic diversity for the maintenance of sexual reproduction. Here, we evaluate patterns of intra- and interpopulation genetic diversity in sexual and asexual populations of Aptinothrips rufus grass thrips. Asexual A. rufus populations are found throughout the world, whereas sexual populations appear to be confined to few locations in the Mediterranean region. We found that asexual A. rufus populations are characterized by extremely high levels of genetic diversity, both in comparison with their sexual relatives and in comparison with other asexual species. Migration is extensive among asexual populations over large geographic distances, whereas close sexual populations are strongly isolated from each other. The combination of extensive migration with replicate evolution of asexual lineages, and a past demographic expansion in at least one of them, generated high local clone diversities in A. rufus. These high clone diversities in asexual populations may mimic certain benefits conferred by sex via genetic diversity and could help explain the extreme success of asexual A. rufus populations.
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Affiliation(s)
| | - Z Dumas
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
| | - T Schwander
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
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186
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Naseeb S, Carter Z, Minnis D, Donaldson I, Zeef L, Delneri D. Widespread Impact of Chromosomal Inversions on Gene Expression Uncovers Robustness via Phenotypic Buffering. Mol Biol Evol 2016; 33:1679-96. [PMID: 26929245 PMCID: PMC4915352 DOI: 10.1093/molbev/msw045] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The nonrandom gene organization in eukaryotes plays a significant role in genome evolution and function. Chromosomal structural changes impact meiotic fitness and, in several organisms, are associated with speciation and rapid adaptation to different environments. Small sized chromosomal inversions, encompassing few genes, are pervasive in Saccharomyces “sensu stricto” species, while larger inversions are less common in yeasts compared with higher eukaryotes. To explore the effect of gene order on phenotype, reproductive isolation, and gene expression, we engineered 16 Saccharomyces cerevisiae strains carrying all possible paracentric and pericentric inversions between Ty1 elements, a natural substrate for rearrangements. We found that 4 inversions were lethal, while the other 12 did not show any fitness advantage or disadvantage in rich and minimal media. At meiosis, only a weak negative correlation with fitness was seen with the size of the inverted region. However, significantly lower fertility was seen in heterozygote invertant strains carrying recombination hotspots within the breakpoints. Altered transcription was observed throughout the genome rather than being overrepresented within the inversions. In spite of the large difference in gene expression in the inverted strains, mitotic fitness was not impaired in the majority of the 94 conditions tested, indicating that the robustness of the expression network buffers the deleterious effects of structural changes in several environments. Overall, our results support the notion that transcriptional changes may compensate for Ty-mediated rearrangements resulting in the maintenance of a constant phenotype, and suggest that large inversions in yeast are unlikely to be a selectable trait during vegetative growth.
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Affiliation(s)
- Samina Naseeb
- Computational and Evolutionary Biology Research Theme, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Zorana Carter
- Computational and Evolutionary Biology Research Theme, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - David Minnis
- Computational and Evolutionary Biology Research Theme, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Ian Donaldson
- Computational and Evolutionary Biology Research Theme, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Leo Zeef
- Computational and Evolutionary Biology Research Theme, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
| | - Daniela Delneri
- Computational and Evolutionary Biology Research Theme, Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom
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187
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McDonald MJ, Rice DP, Desai MM. Sex speeds adaptation by altering the dynamics of molecular evolution. Nature 2016; 531:233-6. [PMID: 26909573 PMCID: PMC4855304 DOI: 10.1038/nature17143] [Citation(s) in RCA: 210] [Impact Index Per Article: 26.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Accepted: 01/20/2016] [Indexed: 12/30/2022]
Abstract
Sex and recombination are pervasive throughout nature despite their substantial costs1. Understanding the evolutionary forces that maintain these phenomena is a central challenge in biology2,3. One longstanding hypothesis argues that sex is beneficial because recombination speeds adaptation4. Theory has proposed a number of distinct population genetic mechanisms that could underlie this advantage. For example, sex can promote the fixation of beneficial mutations either by alleviating interference competition (the Fisher-Muller effect)5,6 or by separating them from deleterious load (the ruby in the rubbish effect)7,8. Previous experiments confirm that sex can increase the rate of adaptation9–17, but these studies did not observe the evolutionary dynamics that drive this effect at the genomic level. Here, we present the first comparison between the sequence-level dynamics of adaptation in experimental sexual and asexual populations, which allows us to identify the specific mechanisms by which sex speeds adaptation. We find that sex alters the molecular signatures of evolution by changing the spectrum of mutations that fix, and confirm theoretical predictions that it does so by alleviating clonal interference. We also show that substantially deleterious mutations hitchhike to fixation in adapting asexual populations. In contrast, recombination prevents such mutations from fixing. Our results demonstrate that sex both speeds adaptation and alters its molecular signature by allowing natural selection to more efficiently sort beneficial from deleterious mutations.
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Affiliation(s)
- Michael J McDonald
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA.,FAS Center for Systems Biology, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Daniel P Rice
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA.,FAS Center for Systems Biology, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Michael M Desai
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA.,FAS Center for Systems Biology, Harvard University, Cambridge, Massachusetts 02138, USA.,Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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188
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Stelkens RB, Miller EL, Greig D. Asynchronous spore germination in isogenic natural isolates ofSaccharomyces paradoxus. FEMS Yeast Res 2016; 16:fow012. [DOI: 10.1093/femsyr/fow012] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/10/2016] [Indexed: 12/18/2022] Open
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189
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Ortiz-Barrientos D, Engelstädter J, Rieseberg LH. Recombination Rate Evolution and the Origin of Species. Trends Ecol Evol 2016; 31:226-236. [PMID: 26831635 DOI: 10.1016/j.tree.2015.12.016] [Citation(s) in RCA: 102] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2015] [Revised: 12/14/2015] [Accepted: 12/22/2015] [Indexed: 12/13/2022]
Abstract
A recipe for dissolving incipient species into a continuum of phenotypes is to recombine their genetic material. Therefore, students of speciation have become increasingly interested in the mechanisms by which recombination between locally adapted lineages is reduced. Evidence abounds that chromosomal rearrangements, via their suppression of recombination during meiosis in hybrids, play a major role in adaptation and speciation. By contrast, genic modifiers of recombination rates have been largely ignored in studies of speciation. We show how both types of reduction in recombination rates facilitate divergence in the face of gene flow, including the early stages of adaptive divergence, the persistence of species after secondary contact, and reinforcement.
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Affiliation(s)
- Daniel Ortiz-Barrientos
- The University of Queensland, School of Biological Sciences, St. Lucia, Queensland, Australia.
| | - Jan Engelstädter
- The University of Queensland, School of Biological Sciences, St. Lucia, Queensland, Australia
| | - Loren H Rieseberg
- University of British Columbia, Department of Botany, Vancouver, British Columbia, Canada; Indiana University, Biology Department, Bloomington, IN 47405-7005, USA
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190
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Rastas P, Calboli FCF, Guo B, Shikano T, Merilä J. Construction of Ultradense Linkage Maps with Lep-MAP2: Stickleback F2 Recombinant Crosses as an Example. Genome Biol Evol 2015; 8:78-93. [PMID: 26668116 PMCID: PMC4758246 DOI: 10.1093/gbe/evv250] [Citation(s) in RCA: 84] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
High-density linkage maps are important tools for genome biology and evolutionary genetics by quantifying the extent of recombination, linkage disequilibrium, and chromosomal rearrangements across chromosomes, sexes, and populations. They provide one of the best ways to validate and refine de novo genome assemblies, with the power to identify errors in assemblies increasing with marker density. However, assembly of high-density linkage maps is still challenging due to software limitations. We describe Lep-MAP2, a software for ultradense genome-wide linkage map construction. Lep-MAP2 can handle various family structures and can account for achiasmatic meiosis to gain linkage map accuracy. Simulations show that Lep-MAP2 outperforms other available mapping software both in computational efficiency and accuracy. When applied to two large F2-generation recombinant crosses between two nine-spined stickleback (Pungitius pungitius) populations, it produced two high-density (∼6 markers/cM) linkage maps containing 18,691 and 20,054 single nucleotide polymorphisms. The two maps showed a high degree of synteny, but female maps were 1.5–2 times longer than male maps in all linkage groups, suggesting genome-wide recombination suppression in males. Comparison with the genome sequence of the three-spined stickleback (Gasterosteus aculeatus) revealed a high degree of interspecific synteny with a low frequency (<5%) of interchromosomal rearrangements. However, a fairly large (ca. 10 Mb) translocation from autosome to sex chromosome was detected in both maps. These results illustrate the utility and novel features of Lep-MAP2 in assembling high-density linkage maps, and their usefulness in revealing evolutionarily interesting properties of genomes, such as strong genome-wide sex bias in recombination rates.
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Affiliation(s)
- Pasi Rastas
- Metapopulation Research Group, Department of Biosciences, University of Helsinki, Helsinki, Finland Department of Zoology, University of Cambridge, Cambridge, United Kingdom
| | - Federico C F Calboli
- Ecological Genetics Research Unit, Department of Biosciences, University of Helsinki, Helsinki, Finland
| | - Baocheng Guo
- Ecological Genetics Research Unit, Department of Biosciences, University of Helsinki, Helsinki, Finland
| | - Takahito Shikano
- Ecological Genetics Research Unit, Department of Biosciences, University of Helsinki, Helsinki, Finland
| | - Juha Merilä
- Ecological Genetics Research Unit, Department of Biosciences, University of Helsinki, Helsinki, Finland
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191
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Abstract
Evolution and maintenance of genetic recombination and its relation to the mutational process is a long-standing, fundamental problem in evolutionary biology that is linked to the general problem of evolution of evolvability. We explored a stochastic model of the evolution of recombination using additive fitness and infinite allele assumptions but no assumptions on the sign or magnitude of the epistasis and the distribution of mutation effects. In this model, fluctuating negative epistasis and predominantly deleterious mutations arise naturally as a consequence of the additive fitness and a reservoir from which new alleles arrive with a fixed distribution of fitness effects. Analysis of the model revealed a nonmonotonic effect of recombination intensity on fitness, with an optimal recombination rate value which maximized fitness in steady state. The optimal recombination rate depended on the mutation rate and was evolvable, that is, subject to selection. The predictions of the model were compatible with the observations on the dependence between genome rearrangement rate and gene flux in microbial genomes.
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Affiliation(s)
- Alexander E Lobkovsky
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, Maryland
| | - Yuri I Wolf
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, Maryland
| | - Eugene V Koonin
- National Center for Biotechnology Information, National Library of Medicine, National Institutes of Health, Bethesda, Maryland
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192
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Zhan T, Boutros M. Towards a compendium of essential genes - From model organisms to synthetic lethality in cancer cells. Crit Rev Biochem Mol Biol 2015; 51:74-85. [PMID: 26627871 PMCID: PMC4819810 DOI: 10.3109/10409238.2015.1117053] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Essential genes are defined by their requirement to sustain life in cells or whole organisms. The systematic identification of essential gene sets not only allows insights into the fundamental building blocks of life, but may also provide novel therapeutic targets in oncology. The discovery of essential genes has been tightly linked to the development and deployment of various screening technologies. Here, we describe how gene essentiality was addressed in different eukaryotic model organisms, covering a range of organisms from yeast to mouse. We describe how increasing knowledge of evolutionarily divergent genomes facilitate identification of gene essentiality across species. Finally, the impact of gene essentiality and synthetic lethality on cancer research and the clinical translation of screening results are highlighted.
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Affiliation(s)
- Tianzuo Zhan
- a Department of Cell and Molecular Biology , Division of Signaling and Functional Genomics, Medical Faculty Mannheim, German Cancer Research Center (DKFZ), Heidelberg University , Heidelberg , Germany and.,b Department of Medicine II , Medical Faculty Mannheim, University Hospital Mannheim, Heidelberg University , Mannheim , Germany
| | - Michael Boutros
- a Department of Cell and Molecular Biology , Division of Signaling and Functional Genomics, Medical Faculty Mannheim, German Cancer Research Center (DKFZ), Heidelberg University , Heidelberg , Germany and
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193
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Cattle Sex-Specific Recombination and Genetic Control from a Large Pedigree Analysis. PLoS Genet 2015; 11:e1005387. [PMID: 26540184 PMCID: PMC4634960 DOI: 10.1371/journal.pgen.1005387] [Citation(s) in RCA: 121] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Accepted: 06/23/2015] [Indexed: 11/19/2022] Open
Abstract
Meiotic recombination is an essential biological process that generates genetic diversity and ensures proper segregation of chromosomes during meiosis. From a large USDA dairy cattle pedigree with over half a million genotyped animals, we extracted 186,927 three-generation families, identified over 8.5 million maternal and paternal recombination events, and constructed sex-specific recombination maps for 59,309 autosomal SNPs. The recombination map spans for 25.5 Morgans in males and 23.2 Morgans in females, for a total studied region of 2,516 Mb (986 kb/cM in males and 1,085 kb/cM in females). The male map is 10% longer than the female map and the sex difference is most pronounced in the subtelomeric regions. We identified 1,792 male and 1,885 female putative recombination hotspots, with 720 hotspots shared between sexes. These hotspots encompass 3% of the genome but account for 25% of the genome-wide recombination events in both sexes. During the past forty years, males showed a decreasing trend in recombination rate that coincided with the artificial selection for milk production. Sex-specific GWAS analyses identified PRDM9 and CPLX1 to have significant effects on genome-wide recombination rate in both sexes. Two novel loci, NEK9 and REC114, were associated with recombination rate in both sexes, whereas three loci, MSH4, SMC3 and CEP55, affected recombination rate in females only. Among the multiple PRDM9 paralogues on the bovine genome, our GWAS of recombination hotspot usage together with linkage analysis identified the PRDM9 paralogue on chromosome 1 to be associated in the U.S. Holstein data. Given the largest sample size ever reported for such studies, our results reveal new insights into the understanding of cattle and mammalian recombination.
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194
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Reding L, Cummings ME. Does sensory expansion benefit asexual species? An olfactory discrimination test in Amazon mollies. Behav Ecol 2015. [DOI: 10.1093/beheco/arv168] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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195
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The Effects of Background and Interference Selection on Patterns of Genetic Variation in Subdivided Populations. Genetics 2015; 201:1539-54. [PMID: 26434720 DOI: 10.1534/genetics.115.178558] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2015] [Accepted: 09/24/2015] [Indexed: 11/18/2022] Open
Abstract
It is well known that most new mutations that affect fitness exert deleterious effects and that natural populations are often composed of subpopulations (demes) connected by gene flow. To gain a better understanding of the joint effects of purifying selection and population structure, we focus on a scenario where an ancestral population splits into multiple demes and study neutral diversity patterns in regions linked to selected sites. In the background selection regime of strong selection, we first derive analytic equations for pairwise coalescent times and FST as a function of time after the ancestral population splits into two demes and then construct a flexible coalescent simulator that can generate samples under complex models such as those involving multiple demes or nonconservative migration. We have carried out extensive forward simulations to show that the new methods can accurately predict diversity patterns both in the nonequilibrium phase following the split of the ancestral population and in the equilibrium between mutation, migration, drift, and selection. In the interference selection regime of many tightly linked selected sites, forward simulations provide evidence that neutral diversity patterns obtained from both the nonequilibrium and equilibrium phases may be virtually indistinguishable for models that have identical variance in fitness, but are nonetheless different with respect to the number of selected sites and the strength of purifying selection. This equivalence in neutral diversity patterns suggests that data collected from subdivided populations may have limited power for differentiating among the selective pressures to which closely linked selected sites are subject.
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196
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Smukowski Heil CS, Ellison C, Dubin M, Noor MAF. Recombining without Hotspots: A Comprehensive Evolutionary Portrait of Recombination in Two Closely Related Species of Drosophila. Genome Biol Evol 2015; 7:2829-42. [PMID: 26430062 PMCID: PMC4684701 DOI: 10.1093/gbe/evv182] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/03/2015] [Indexed: 12/12/2022] Open
Abstract
Meiotic recombination rate varies across the genome within and between individuals, populations, and species in virtually all taxa studied. In almost every species, this variation takes the form of discrete recombination hotspots, determined in some mammals by a protein called PRDM9. Hotspots and their determinants have a profound effect on the genomic landscape, and share certain features that extend across the tree of life. Drosophila, in contrast, are anomalous in their absence of hotspots, PRDM9, and other species-specific differences in the determination of recombination. To better understand the evolution of meiosis and general patterns of recombination across diverse taxa, we present a truly comprehensive portrait of recombination across time, combining recently published cross-based contemporary recombination estimates from each of two sister species with newly obtained linkage-disequilibrium-based historic estimates of recombination from both of these species. Using Drosophila pseudoobscura and Drosophila miranda as a model system, we compare recombination rate between species at multiple scales, and we suggest that Drosophila replicate the pattern seen in human-chimpanzee in which recombination rate is conserved at broad scales. We also find evidence of a species-wide recombination modifier(s), resulting in both a present and historic genome-wide elevation of recombination rates in D. miranda, and identify broad scale effects on recombination from the presence of an inversion. Finally, we reveal an unprecedented view of the distribution of recombination in D. pseudoobscura, illustrating patterns of linked selection and where recombination is taking place. Overall, by combining these estimation approaches, we highlight key similarities and differences in recombination between Drosophila and other organisms.
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Affiliation(s)
- Caiti S Smukowski Heil
- Biology Department, Duke University Genome Sciences Department, University of Washington
| | - Chris Ellison
- Department of Integrative Biology, University of California, Berkeley
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197
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Ashu EE, Xu J. The roles of sexual and asexual reproduction in the origin and dissemination of strains causing fungal infectious disease outbreaks. INFECTION GENETICS AND EVOLUTION 2015; 36:199-209. [PMID: 26394109 DOI: 10.1016/j.meegid.2015.09.019] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2015] [Revised: 09/16/2015] [Accepted: 09/18/2015] [Indexed: 12/15/2022]
Abstract
Sexual reproduction commonly refers to the reproductive process in which genomes from two sources are combined into a single cell through mating and then the zygote genomes are partitioned to progeny cells through meiosis. Reproduction in the absence of mating and meiosis is referred to as asexual or clonal reproduction. One major advantage of sexual reproduction is that it generates genetic variation among progeny which may allow for faster adaptation of the population to novel and/or stressful environments. However, adaptation to stressful or new environments can still occur through mutation, in the absence of sex. In this review, we analyzed the relative contributions of sexual and asexual reproduction in the origin and spread of strains causing fungal infectious diseases outbreaks. The necessity of sex and the ability of asexual fungi to initiate outbreaks are discussed. We propose a framework that relates the modes of reproduction to the origin and propagation of fungal disease outbreaks. Our analyses suggest that both sexual and asexual reproduction can play critical roles in the origin of outbreak strains and that the rapid spread of outbreak strains is often accomplished through asexual expansion.
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Affiliation(s)
- Eta Ebasi Ashu
- Department of Biology, McMaster University, 1280 Main St. W, Hamilton, ON L8S 4K1, Canada
| | - Jianping Xu
- Department of Biology, McMaster University, 1280 Main St. W, Hamilton, ON L8S 4K1, Canada.
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198
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The Impact of Recombination Hotspots on Genome Evolution of a Fungal Plant Pathogen. Genetics 2015; 201:1213-28. [PMID: 26392286 DOI: 10.1534/genetics.115.180968] [Citation(s) in RCA: 73] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2015] [Accepted: 09/17/2015] [Indexed: 12/30/2022] Open
Abstract
Recombination has an impact on genome evolution by maintaining chromosomal integrity, affecting the efficacy of selection, and increasing genetic variability in populations. Recombination rates are a key determinant of the coevolutionary dynamics between hosts and their pathogens. Historic recombination events created devastating new pathogens, but the impact of ongoing recombination in sexual pathogens is poorly understood. Many fungal pathogens of plants undergo regular sexual cycles, and sex is considered to be a major factor contributing to virulence. We generated a recombination map at kilobase-scale resolution for the haploid plant pathogenic fungus Zymoseptoria tritici. To account for intraspecific variation in recombination rates, we constructed genetic maps from two independent crosses. We localized a total of 10,287 crossover events in 441 progeny and found that recombination rates were highly heterogeneous within and among chromosomes. Recombination rates on large chromosomes were inversely correlated with chromosome length. Short accessory chromosomes often lacked evidence for crossovers between parental chromosomes. Recombination was concentrated in narrow hotspots that were preferentially located close to telomeres. Hotspots were only partially conserved between the two crosses, suggesting that hotspots are short-lived and may vary according to genomic background. Genes located in hotspot regions were enriched in genes encoding secreted proteins. Population resequencing showed that chromosomal regions with high recombination rates were strongly correlated with regions of low linkage disequilibrium. Hence, genes in pathogen recombination hotspots are likely to evolve faster in natural populations and may represent a greater threat to the host.
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Limborg MT, Waples RK, Allendorf FW, Seeb JE. Linkage Mapping Reveals Strong Chiasma Interference in Sockeye Salmon: Implications for Interpreting Genomic Data. G3 (BETHESDA, MD.) 2015; 5:2463-73. [PMID: 26384769 PMCID: PMC4632065 DOI: 10.1534/g3.115.020222] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/07/2015] [Accepted: 09/14/2015] [Indexed: 01/15/2023]
Abstract
Meiotic recombination is fundamental for generating new genetic variation and for securing proper disjunction. Further, recombination plays an essential role during the rediploidization process of polyploid-origin genomes because crossovers between pairs of homeologous chromosomes retain duplicated regions. A better understanding of how recombination affects genome evolution is crucial for interpreting genomic data; unfortunately, current knowledge mainly originates from a few model species. Salmonid fishes provide a valuable system for studying the effects of recombination in nonmodel species. Salmonid females generally produce thousands of embryos, providing large families for conducting inheritance studies. Further, salmonid genomes are currently rediploidizing after a whole genome duplication and can serve as models for studying the role of homeologous crossovers on genome evolution. Here, we present a detailed interrogation of recombination patterns in sockeye salmon (Oncorhynchus nerka). First, we use RAD sequencing of haploid and diploid gynogenetic families to construct a dense linkage map that includes paralogous loci and location of centromeres. We find a nonrandom distribution of paralogs that mainly cluster in extended regions distally located on 11 different chromosomes, consistent with ongoing homeologous recombination in these regions. We also estimate the strength of interference across each chromosome; results reveal strong interference and crossovers are mostly limited to one per arm. Interference was further shown to continue across centromeres, but metacentric chromosomes generally had at least one crossover on each arm. We discuss the relevance of these findings for both mapping and population genomic studies.
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Affiliation(s)
- Morten T Limborg
- School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington 98195 National Institute of Aquatic Resources, Technical University of Denmark, Vejlsøvej 39, Silkeborg, Denmark
| | - Ryan K Waples
- School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington 98195
| | - Fred W Allendorf
- Division of Biological Sciences, University of Montana, Missoula, Montana 59812
| | - James E Seeb
- School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington 98195
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Abstract
PURPOSE OF REVIEW An improved understanding of how recombination affects the evolutionary history of HIV is crucial to understand its current and future evolution. The present review aims to disentangle the manifold effects of recombination on HIV by discussing its effects on the evolutionary history and the adaptive potential of HIV in the context of concepts from evolutionary genetics and genomics. RECENT FINDINGS The increasing occurrence of secondary contacts between divergent subtype populations (during coinfection) results in increased observations of recombinants worldwide. Recombination is heterogeneous along the HIV genome. Consequences of recombination of HIV evolution are, in combination with other demographic processes, expected to either homogenize the genetic composition of HIV populations (homogenization) or provide the potential for novel adaptations (diversification). New methods in population genomics allow deep characterization of recombinant genome (the segment composition and origin) and their evolutionary trajectories. SUMMARY HIV recombinants increase worldwide and invade geographical regions where pure subtypes were previously predominant. This trend is expected to continue in the future, as ease to travel worldwide increases opportunities for recombination between divergent HIV strains. While the effects of recombination in HIV are much researched, more effort is required to characterize current HIV recombinant composition and dynamics. This can be achieved with new population genetic and genomic methods.
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