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Abstract
The high prevalence of sexual reproduction is considered a paradox mainly for two reasons. First, asexuals should enjoy various growth benefits because they seemingly rid themselves of the many inefficiencies of sexual reproduction-the so-called costs of sex. Second, there seems to be no lack of asexual origins because losses of sexual reproduction have been described in almost every larger eukaryotic taxon. Current attempts to resolve this paradox concentrate on a few hypotheses that provide universal benefits that would compensate for these costs and give sexual reproduction a net advantage. However, are new asexual lineages really those powerful invaders that could quickly displace their sexual ancestors? Research on the costs of sex indicates that sex is often stabilized by highly lineage-specific mechanisms. Two main categories can be distinguished. First are beneficial traits that evolved within a particular species and became tightly associated with sex (e.g., a mating system that involves sexual selection, or a sexual diapausing stage that allows survival through harsh periods). If such traits are absent in asexuals, simple growth efficiency considerations will not capture the fitness benefits gained by skipping sexual reproduction. Second, lineage-specific factors might prevent asexuals from reaching their full potential (e.g., dependence on fertilization in sperm-dependent parthenogens). Such observations suggest that the costs of sex are highly variable and often lower than theoretical considerations suggest. This has implications for the magnitude of universal benefits required to resolve the paradox of sex.
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152
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Abstract
Bacteria reproduce asexually and pass on a single genome copied from the parent, a reproductive mode that assures the clonal descent of progeny; however, a truly clonal bacterial species is extremely rare. The signal of clonality can be interrupted by gene uptake and exchange, initiating homologous recombination that results in the unique sequence of one clone being incorporated into another. Because recombination occurs sporadically and on local scales, these events are often difficult to recognize, even when considering large samples of completely sequenced genomes. Moreover, several processes can produce the appearance of clonality in populations that undergo frequent recombination. The rates and consequences of recombination have been studied in Escherichia coli for over 40 y, and, during this time, there have been several shifting views of its clonal status, population structure, and rates of gene exchange. We reexamine the studies and retrace the evolution of the methods that have assessed the extent of DNA flux, largely focusing on its impact on the E. coli genome.
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153
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Affiliation(s)
- Jennifer L Modliszewski
- Department of Biology and the Carolina Center for Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599-3280, USA
| | - Gregory P Copenhaver
- Department of Biology and the Carolina Center for Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599-3280, USA
- Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, NC, 27599-3280, USA
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154
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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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155
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Toyota K, Miyakawa H, Hiruta C, Furuta K, Ogino Y, Shinoda T, Tatarazako N, Miyagawa S, Shaw JR, Iguchi T. Methyl farnesoate synthesis is necessary for the environmental sex determination in the water flea Daphnia pulex. JOURNAL OF INSECT PHYSIOLOGY 2015; 80:22-30. [PMID: 25721056 DOI: 10.1016/j.jinsphys.2015.02.002] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2014] [Revised: 02/04/2015] [Accepted: 02/06/2015] [Indexed: 06/04/2023]
Abstract
Sex-determination systems can be divided into two groups: genotypic sex determination (GSD) and environmental sex determination (ESD). ESD is an adaptive life-history strategy that allows control of sex in response to environmental cues in order to optimize fitness. However, the molecular basis of ESD remains largely unknown. The micro crustacean Daphnia pulex exhibits ESD in response to various external stimuli. Although methyl farnesoate (MF: putative juvenile hormone, JH, in daphnids) has been reported to induce male production in daphnids, the role of MF as a sex-determining factor remains elusive due to the lack of a suitable model system for its study. Here, we establish such a system for ESD studies in D. pulex. The WTN6 strain switches from producing females to producing males in response to the shortened day condition, while the MFP strain only produces females, irrespective of day-length. To clarify whether MF has a novel physiological role as a sex-determining factor in D. pulex, we demonstrate that a MF/JH biosynthesis inhibitor suppressed male production in WTN6 strain reared under the male-inducible condition, shortened day-length. Moreover, we show that juvenile hormone acid O-methyltransferase (JHAMT), a critical enzyme of MF/JH biosynthesis, displays MF-generating activity by catalyzing farnesoic acid. Expression of the JHAMT gene increased significantly just before the MF-sensitive period for male production in the WTN6 strain, but not in the MFP strain, when maintained under male-inducible conditions. These results suggest that MF synthesis regulated by JHAMT is necessary for male offspring production in D. pulex. Our findings provide novel insights into the genetic underpinnings of ESD and they begin to shed light on the physiological function of MF as a male-fate determiner in D. pulex.
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Affiliation(s)
- Kenji Toyota
- Department of Basic Biology, Faculty of Life Science, Graduate University for Advanced Studies (SOKENDAI), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan; Okazaki Institute for Integrative Bioscience, National Institute for Basic Biology, and National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan
| | - Hitoshi Miyakawa
- Okazaki Institute for Integrative Bioscience, National Institute for Basic Biology, and National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan
| | - Chizue Hiruta
- Okazaki Institute for Integrative Bioscience, National Institute for Basic Biology, and National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan; Department of Biology, Center for Liberal Arts and Sciences, Iwate Medical University, 2-1-1, Nishi-Tokuda, Yahaba-cho, Shiwa-gun, Iwate 028-3694, Japan
| | - Kenjiro Furuta
- Department of Life Science and Biotechnology, Faculty of Life and Environmental Science, Shimane University, Matsue, Shimane 690-8504, Japan
| | - Yukiko Ogino
- Department of Basic Biology, Faculty of Life Science, Graduate University for Advanced Studies (SOKENDAI), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan; Okazaki Institute for Integrative Bioscience, National Institute for Basic Biology, and National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan
| | - Tetsuro Shinoda
- National Institute of Agrobiological Sciences, 1-2, Oowashi, Tsukuba, Ibaraki 305-8634, Japan
| | - Norihisa Tatarazako
- National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan
| | - Shinichi Miyagawa
- Department of Basic Biology, Faculty of Life Science, Graduate University for Advanced Studies (SOKENDAI), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan; Okazaki Institute for Integrative Bioscience, National Institute for Basic Biology, and National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan
| | - Joseph R Shaw
- School of Public and Environmental Affairs, Indiana University, 1315 East Tenth Street, Bloomington, IN 47405, USA; School of Biosciences, University of Birmingham, Birmingham B15 2TT, UK
| | - Taisen Iguchi
- Department of Basic Biology, Faculty of Life Science, Graduate University for Advanced Studies (SOKENDAI), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan; Okazaki Institute for Integrative Bioscience, National Institute for Basic Biology, and National Institutes of Natural Sciences, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan.
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156
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Joschinski J, van Kleunen M, Stift M. Costs associated with the evolution of selfing in North American populations of Arabidopsis lyrata? Evol Ecol 2015. [DOI: 10.1007/s10682-015-9786-3] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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157
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Perales C, Moreno E, Domingo E. Clonality and intracellular polyploidy in virus evolution and pathogenesis. Proc Natl Acad Sci U S A 2015; 112:8887-92. [PMID: 26195777 PMCID: PMC4517279 DOI: 10.1073/pnas.1501715112] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In the present article we examine clonality in virus evolution. Most viruses retain an active recombination machinery as a potential means to initiate new levels of genetic exploration that go beyond those attainable solely by point mutations. However, despite abundant recombination that may be linked to molecular events essential for genome replication, herein we provide evidence that generation of recombinants with altered biological properties is not essential for the completion of the replication cycles of viruses, and that viral lineages (near-clades) can be defined. We distinguish mechanistically active but inconsequential recombination from evolutionarily relevant recombination, illustrated by episodes in the field and during experimental evolution. In the field, recombination has been at the origin of new viral pathogens, and has conferred fitness advantages to some viruses once the parental viruses have attained a sufficient degree of diversification by point mutations. In the laboratory, recombination mediated a salient genome segmentation of foot-and-mouth disease virus, an important animal pathogen whose genome in nature has always been characterized as unsegmented. We propose a model of continuous mutation and recombination, with punctuated, biologically relevant recombination events for the survival of viruses, both as disease agents and as promoters of cellular evolution. Thus, clonality is the standard evolutionary mode for viruses because recombination is largely inconsequential, since the decisive events for virus replication and survival are not dependent on the exchange of genetic material and formation of recombinant (mosaic) genomes.
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Affiliation(s)
- Celia Perales
- Centro de Biologia Molecular "Severo Ochoa" (CSIC-UAM), Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, E-28049 Madrid, Spain; Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas, Barcelona, Spain; and Liver Unit, Internal Medicine, Laboratory of Malalties Hepàtiques, Vall d'Hebron Institut de Recerca-Hospital Universitari Vall d'Hebron, Universitat Autònoma de Barcelona, 08035 Barcelona, Spain
| | - Elena Moreno
- Centro de Biologia Molecular "Severo Ochoa" (CSIC-UAM), Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, E-28049 Madrid, Spain
| | - Esteban Domingo
- Centro de Biologia Molecular "Severo Ochoa" (CSIC-UAM), Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, E-28049 Madrid, Spain; Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas, Barcelona, Spain; and
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158
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Carranza J, Polo V. Sexual reproduction with variable mating systems can resist asexuality in a rock-paper-scissors dynamics. ROYAL SOCIETY OPEN SCIENCE 2015; 2:140383. [PMID: 26587254 PMCID: PMC4632567 DOI: 10.1098/rsos.140383] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/29/2014] [Accepted: 06/18/2015] [Indexed: 06/05/2023]
Abstract
While sex can be advantageous for a lineage in the long term, we still lack an explanation for its maintenance with the twofold cost per generation. Here we model an infinite diploid population where two autosomal loci determine, respectively, the reproductive mode, sexual versus asexual and the mating system, polygynous (costly sex) versus monogamous (assuming equal contribution of parents to offspring, i.e. non-costly sex). We show that alleles for costly sex can spread when non-costly sexual modes buffer the interaction between asexual and costly sexual strategies, even without twofold benefit of recombination with respect to asexuality. The three interacting strategies have intransitive fitness relationships leading to a rock-paper-scissors dynamics, so that alleles for costly sex cannot be eliminated by asexuals in most situations throughout the parameter space. Our results indicate that sexual lineages with variable mating systems can resist the invasion of asexuals and allow for long-term effects to accumulate, thus providing a solution to the persisting theoretical question of why sex was not displaced by asexuality along evolution.
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Affiliation(s)
- Juan Carranza
- Department of Zoology, CRCP Research Center, University of Córdoba, Córdoba 14071, Spain
- Biology and Ethology Unit, University of Extremadura, Cáceres 10071, Spain
| | - Vicente Polo
- Departamento de Biología y Geología del Área de Biodiversidad y Conservación, Escuela Superior de Ciencias Experimentales y Tecnología (ESCET), Universidad Rey Juan Carlos, Madrid, Spain
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159
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Beabout K, Hammerstrom TG, Wang TT, Bhatty M, Christie PJ, Saxer G, Shamoo Y. Rampant Parasexuality Evolves in a Hospital Pathogen during Antibiotic Selection. Mol Biol Evol 2015; 32:2585-97. [PMID: 26060280 DOI: 10.1093/molbev/msv133] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Horizontal gene transfer threatens the therapeutic success of antibiotics by facilitating the rapid dissemination of resistance alleles among bacterial species. The conjugative mobile element Tn916 provides an excellent context for examining the role of adaptive parasexuality as it carries the tetracycline-resistance allele tetM and has been identified in a wide range of pathogens. We have used a combination of experimental evolution and allelic frequency measurements to gain insights into the adaptive trajectories leading to tigecycline resistance in a hospital strain of Enterococcus faecalis and predict what mechanisms of resistance are most likely to appear in the clinical setting. Here, we show that antibiotic selection led to the near fixation of adaptive alleles that simultaneously altered TetM expression and produced remarkably increased levels of Tn916 horizontal gene transfer. In the absence of drug, approximately 1 in 120,000 of the nonadapted E. faecalis S613 cells had an excised copy of Tn916, whereas nearly 1 in 50 cells had an excised copy of Tn916 upon selection for resistance resulting in a more than 1,000-fold increase in conjugation rates. We also show that tigecycline, a translation inhibitor, selected for a mutation in the ribosomal S10 protein. Our results show the first example of mutations that concurrently confer resistance to an antibiotic and lead to constitutive conjugal-transfer of the resistance allele. Selection created a highly parasexual phenotype and high frequency of Tn916 jumping demonstrating how the use of antibiotics can lead directly to the proliferation of resistance in, and potentially among, pathogens.
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Affiliation(s)
| | | | - Tim T Wang
- Department of BioSciences, Rice University
| | - Minny Bhatty
- Department of Microbiology and Molecular Genetics, University of Texas Medical School at Houston
| | - Peter J Christie
- Department of Microbiology and Molecular Genetics, University of Texas Medical School at Houston
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160
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Kleiman M, Hadany L. The evolution of obligate sex: the roles of sexual selection and recombination. Ecol Evol 2015; 5:2572-83. [PMID: 26257871 PMCID: PMC4523354 DOI: 10.1002/ece3.1516] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Revised: 04/20/2015] [Accepted: 04/23/2015] [Indexed: 11/20/2022] Open
Abstract
The evolution of sex is one of the greatest mysteries in evolutionary biology. An even greater mystery is the evolution of obligate sex, particularly when competing with facultative sex and not with complete asexuality. Here, we develop a stochastic simulation of an obligate allele invading a facultative population, where males are subject to sexual selection. We identify a range of parameters where sexual selection can contribute to the evolution of obligate sex: Especially when the cost of sex is low, mutation rate is high, and the facultative individuals do not reproduce sexually very often. The advantage of obligate sex becomes larger in the absence of recombination. Surprisingly, obligate sex can take over even when the population has a lower mean fitness as a result. We show that this is due to the high success of obligate males that can compensate the cost of sex.
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Affiliation(s)
- Maya Kleiman
- Department of Chemistry, Ben-Gurion University of the Negev Be'er-Sheva, 8410501, Israel
| | - Lilach Hadany
- Department of Molecular Biology and Ecology of Plants, Faculty of Life Sciences, Tel Aviv University Ramat Aviv, 69978, Israel
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161
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Zeldovich KB, Liu P, Renzette N, Foll M, Pham ST, Venev SV, Gallagher GR, Bolon DN, Kurt-Jones EA, Jensen JD, Caffrey DR, Schiffer CA, Kowalik TF, Wang JP, Finberg RW. Positive Selection Drives Preferred Segment Combinations during Influenza Virus Reassortment. Mol Biol Evol 2015; 32:1519-32. [PMID: 25713211 PMCID: PMC4462674 DOI: 10.1093/molbev/msv044] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Influenza A virus (IAV) has a segmented genome that allows for the exchange of genome segments between different strains. This reassortment accelerates evolution by breaking linkage, helping IAV cross species barriers to potentially create highly virulent strains. Challenges associated with monitoring the process of reassortment in molecular detail have limited our understanding of its evolutionary implications. We applied a novel deep sequencing approach with quantitative analysis to assess the in vitro temporal evolution of genomic reassortment in IAV. The combination of H1N1 and H3N2 strains reproducibly generated a new H1N2 strain with the hemagglutinin and nucleoprotein segments originating from H1N1 and the remaining six segments from H3N2. By deep sequencing the entire viral genome, we monitored the evolution of reassortment, quantifying the relative abundance of all IAV genome segments from the two parent strains over time and measuring the selection coefficients of the reassorting segments. Additionally, we observed several mutations coemerging with reassortment that were not found during passaging of pure parental IAV strains. Our results demonstrate how reassortment of the segmented genome can accelerate viral evolution in IAV, potentially enabled by the emergence of a small number of individual mutations.
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Affiliation(s)
- Konstantin B Zeldovich
- Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, Worcester
| | - Ping Liu
- Department of Medicine, University of Massachusetts Medical School, Worcester
| | - Nicholas Renzette
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester
| | - Matthieu Foll
- École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland Swiss Institute of Bioinformatics (SIB), Lausanne, Switzerland
| | - Serena T Pham
- Department of Medicine, University of Massachusetts Medical School, Worcester
| | - Sergey V Venev
- Program in Bioinformatics and Integrative Biology, University of Massachusetts Medical School, Worcester
| | - Glen R Gallagher
- Department of Medicine, University of Massachusetts Medical School, Worcester
| | - Daniel N Bolon
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester
| | - Evelyn A Kurt-Jones
- Department of Medicine, University of Massachusetts Medical School, Worcester
| | - Jeffrey D Jensen
- École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland Swiss Institute of Bioinformatics (SIB), Lausanne, Switzerland
| | - Daniel R Caffrey
- Department of Medicine, University of Massachusetts Medical School, Worcester
| | - Celia A Schiffer
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester
| | - Timothy F Kowalik
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester
| | - Jennifer P Wang
- Department of Medicine, University of Massachusetts Medical School, Worcester
| | - Robert W Finberg
- Department of Medicine, University of Massachusetts Medical School, Worcester
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162
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Abstract
Eukaryotes were born of a chimeric union between two prokaryotes--the progenitors of the mitochondrial and nuclear genomes. Early in eukaryote evolution, most mitochondrial genes were lost or transferred to the nucleus, but a core set of genes that code exclusively for products associated with the electron transport system remained in the mitochondrion. The products of these mitochondrial genes work in intimate association with the products of nuclear genes to enable oxidative phosphorylation and core energy production. The need for coadaptation, the challenge of cotransmission, and the possibility of genomic conflict between mitochondrial and nuclear genes have profound consequences for the ecology and evolution of eukaryotic life. An emerging interdisciplinary field that I call "mitonuclear ecology" is reassessing core concepts in evolutionary ecology including sexual reproduction, two sexes, sexual selection, adaptation, and speciation in light of the interactions of mitochondrial and nuclear genomes.
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163
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Ziolkowski PA, Berchowitz LE, Lambing C, Yelina NE, Zhao X, Kelly KA, Choi K, Ziolkowska L, June V, Sanchez-Moran E, Franklin C, Copenhaver GP, Henderson IR. Juxtaposition of heterozygous and homozygous regions causes reciprocal crossover remodelling via interference during Arabidopsis meiosis. eLife 2015; 4:e03708. [PMID: 25815584 PMCID: PMC4407271 DOI: 10.7554/elife.03708] [Citation(s) in RCA: 76] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2014] [Accepted: 03/26/2015] [Indexed: 12/13/2022] Open
Abstract
During meiosis homologous chromosomes undergo crossover recombination. Sequence differences between homologs can locally inhibit crossovers. Despite this, nucleotide diversity and population-scaled recombination are positively correlated in eukaryote genomes. To investigate interactions between heterozygosity and recombination we crossed Arabidopsis lines carrying fluorescent crossover reporters to 32 diverse accessions and observed hybrids with significantly higher and lower crossovers than homozygotes. Using recombinant populations derived from these crosses we observed that heterozygous regions increase crossovers when juxtaposed with homozygous regions, which reciprocally decrease. Total crossovers measured by chiasmata were unchanged when heterozygosity was varied, consistent with homeostatic control. We tested the effects of heterozygosity in mutants where the balance of interfering and non-interfering crossover repair is altered. Crossover remodeling at homozygosity-heterozygosity junctions requires interference, and non-interfering repair is inefficient in heterozygous regions. As a consequence, heterozygous regions show stronger crossover interference. Our findings reveal how varying homolog polymorphism patterns can shape meiotic recombination.
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Affiliation(s)
- Piotr A Ziolkowski
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
- Department of Biotechnology, Adam Mickiewicz University, Poznań, Poland
| | - Luke E Berchowitz
- Department of Biology and the Carolina Center for Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, United States
- Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, United States
| | - Christophe Lambing
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Nataliya E Yelina
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Xiaohui Zhao
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Krystyna A Kelly
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Kyuha Choi
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Liliana Ziolkowska
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | - Viviana June
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
| | | | - Chris Franklin
- School of Biosciences, University of Birmingham, Birmingham, United Kingdom
| | - Gregory P Copenhaver
- Department of Biology and the Carolina Center for Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, United States
- Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, United States
| | - Ian R Henderson
- Department of Plant Sciences, University of Cambridge, Cambridge, United Kingdom
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164
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Toyota K, Miyakawa H, Yamaguchi K, Shigenobu S, Ogino Y, Tatarazako N, Miyagawa S, Iguchi T. NMDA receptor activation upstream of methyl farnesoate signaling for short day-induced male offspring production in the water flea, Daphnia pulex. BMC Genomics 2015; 16:186. [PMID: 25867484 PMCID: PMC4372037 DOI: 10.1186/s12864-015-1392-9] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2014] [Accepted: 02/24/2015] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The cladoceran crustacean Daphnia pulex produces female offspring by parthenogenesis under favorable conditions, but in response to various unfavorable external stimuli, it produces male offspring (environmental sex determination: ESD). We recently established an innovative system for ESD studies using D. pulex WTN6 strain, in which the sex of the offspring can be controlled simply by changes in the photoperiod: the long-day and short-day conditions can induce female and male offspring, respectively. Taking advantage of this system, we demonstrated that de novo methyl farnesoate (MF) synthesis is necessary for male offspring production. These results indicate the key role of innate MF signaling as a conductor between external environmental stimuli and the endogenous male developmental pathway. Despite these findings, the molecular mechanisms underlying up- and downstream signaling of MF have not yet been well elucidated in D. pulex. RESULTS To elucidate up- and downstream events of MF signaling during sex determination processes, we compared the transcriptomes of daphnids reared under the long-day (female) condition with short-day (male) and MF-treated (male) conditions. We found that genes involved in ionotropic glutamate receptors, known to mediate the vast majority of excitatory neurotransmitting processes in various organisms, were significantly activated in daphnids by the short-day condition but not by MF treatment. Administration of specific agonists and antagonists, especially for the N-methyl-D-aspartic acid (NMDA) receptor, strongly increased or decreased, respectively, the proportion of male-producing mothers. Moreover, we also identified genes responsible for male production (e.g., protein kinase C pathway-related genes). Such genes were generally shared between the short-day reared and MF-treated daphnids. CONCLUSIONS We identified several candidate genes regulating ESD which strongly suggests that these genes may be essential factors for male offspring production as an upstream regulator of MF signaling in D. pulex. This study provides new insight into the fundamental mechanisms underlying how living organisms alter their phenotypes in response to various external environments.
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Affiliation(s)
- Kenji Toyota
- />Department of Basic Biology, Faculty of Life Science, SOKENDAI (The Graduate University for Advanced Studies), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787 Japan
- />National Institute for Basic Biology, 38 Nishigonaka, Myodaiji, Okazaki, Aichi 444-8585 Japan
- />Okazaki Institute for Integrative Bioscience, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787 Japan
| | - Hitoshi Miyakawa
- />National Institute for Basic Biology, 38 Nishigonaka, Myodaiji, Okazaki, Aichi 444-8585 Japan
- />Okazaki Institute for Integrative Bioscience, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787 Japan
| | - Katsushi Yamaguchi
- />National Institute for Basic Biology, 38 Nishigonaka, Myodaiji, Okazaki, Aichi 444-8585 Japan
| | - Shuji Shigenobu
- />Department of Basic Biology, Faculty of Life Science, SOKENDAI (The Graduate University for Advanced Studies), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787 Japan
- />National Institute for Basic Biology, 38 Nishigonaka, Myodaiji, Okazaki, Aichi 444-8585 Japan
| | - Yukiko Ogino
- />Department of Basic Biology, Faculty of Life Science, SOKENDAI (The Graduate University for Advanced Studies), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787 Japan
- />National Institute for Basic Biology, 38 Nishigonaka, Myodaiji, Okazaki, Aichi 444-8585 Japan
- />Okazaki Institute for Integrative Bioscience, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787 Japan
| | - Norihisa Tatarazako
- />National Institute for Environmental Studies, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506 Japan
| | - Shinichi Miyagawa
- />Department of Basic Biology, Faculty of Life Science, SOKENDAI (The Graduate University for Advanced Studies), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787 Japan
- />National Institute for Basic Biology, 38 Nishigonaka, Myodaiji, Okazaki, Aichi 444-8585 Japan
- />Okazaki Institute for Integrative Bioscience, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787 Japan
| | - Taisen Iguchi
- />Department of Basic Biology, Faculty of Life Science, SOKENDAI (The Graduate University for Advanced Studies), 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787 Japan
- />National Institute for Basic Biology, 38 Nishigonaka, Myodaiji, Okazaki, Aichi 444-8585 Japan
- />Okazaki Institute for Integrative Bioscience, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787 Japan
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Vašut RJ, Vijverberg K, van Dijk PJ, de Jong H. Fluorescent in situ hybridization shows DIPLOSPOROUS located on one of the NOR chromosomes in apomictic dandelions (Taraxacum) in the absence of a large hemizygous chromosomal region. Genome 2015; 57:609-20. [PMID: 25760668 DOI: 10.1139/gen-2014-0143] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Apomixis in dandelions (Taraxacum: Asteraceae) is encoded by two unlinked dominant loci and a third yet undefined genetic factor: diplosporous omission of meiosis (DIPLOSPOROUS, DIP), parthenogenetic embryo development (PARTHENOGENESIS, PAR), and autonomous endosperm formation, respectively. In this study, we determined the chromosomal position of the DIP locus in Taraxacum by using fluorescent in situ hybridization (FISH) with bacterial artificial chromosomes (BACs) that genetically map within 1.2-0.2 cM of DIP. The BACs showed dispersed fluorescent signals, except for S4-BAC 83 that displayed strong unique signals as well. Under stringent blocking of repeats by C0t-DNA fragments, only a few fluorescent foci restricted to defined chromosome regions remained, including one on the nucleolus organizer region (NOR) chromosomes that contains the 45S rDNAs. FISH with S4-BAC 83 alone and optimal blocking showed discrete foci in the middle of the long arm of one of the NOR chromosomes only in triploid and tetraploid diplosporous dandelions, while signals in sexual diploids were lacking. This agrees with the genetic model of a single dose, dominant DIP allele, absent in sexuals. The length of the DIP region is estimated to cover a region of 1-10 Mb. FISH in various accessions of Taraxacum and the apomictic sister species Chondrilla juncea, confirmed the chromosomal position of DIP within Taraxacum but not outside the genus. Our results endorse that, compared to other model apomictic species, expressing either diplospory or apospory, the genome of Taraxacum shows a more similar and less diverged chromosome structure at the DIP locus. The different levels of allele sequence divergence at apomeiosis loci may reflect different terms of asexual reproduction. The association of apomeiosis loci with repetitiveness, dispersed repeats, and retrotransposons commonly observed in apomictic species may imply a functional role of these shared features in apomictic reproduction, as is discussed.
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Affiliation(s)
- Radim J Vašut
- Laboratory of Genetics, Wageningen University and Research Centre, P.O. Box 309, NL-6700 AH Wageningen, the Netherlands
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Epigenetic control of meiotic recombination in plants. SCIENCE CHINA-LIFE SCIENCES 2015; 58:223-31. [PMID: 25651968 DOI: 10.1007/s11427-015-4811-x] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Accepted: 12/03/2014] [Indexed: 10/24/2022]
Abstract
Meiotic recombination is a deeply conserved process within eukaryotes that has a profound effect on patterns of natural genetic variation. During meiosis homologous chromosomes pair and undergo DNA double strand breaks generated by the Spo11 endonuclease. These breaks can be repaired as crossovers that result in reciprocal exchange between chromosomes. The frequency of recombination along chromosomes is highly variable, for example, crossovers are rarely observed in heterochromatin and the centromeric regions. Recent work in plants has shown that crossover hotspots occur in gene promoters and are associated with specific chromatin modifications, including H2A.Z. Meiotic chromosomes are also organized in loop-base arrays connected to an underlying chromosome axis, which likely interacts with chromatin to organize patterns of recombination. Therefore, epigenetic information exerts a major influence on patterns of meiotic recombination along chromosomes, genetic variation within populations and evolution of plant genomes.
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167
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Effect of drift, selection and recombination on the equilibrium frequency of deleterious mutations. J Theor Biol 2015; 365:238-46. [PMID: 25451760 DOI: 10.1016/j.jtbi.2014.10.023] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2014] [Revised: 08/30/2014] [Accepted: 10/22/2014] [Indexed: 11/22/2022]
Abstract
We study the stationary state of a population evolving under the action of random genetic drift, selection and recombination in which both deleterious and reverse beneficial mutations can occur. We find that the equilibrium fraction of deleterious mutations decreases as the population size is increased. We calculate exactly the steady state frequency in a nonrecombining population when population size is infinite and for a neutral finite population, and obtain bounds on the fraction of deleterious mutations. We also find that for small and very large populations, the number of deleterious mutations depends weakly on recombination, but for moderately large populations, recombination alleviates the effect of deleterious mutations. An analytical argument shows that recombination decreases disadvantageous mutations appreciably when beneficial mutations are rare as is the case in adapting microbial populations, whereas it has a moderate effect on codon bias where the mutation rates between the preferred and unpreferred codons are comparable.
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168
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Rapid and inexpensive whole-genome genotyping-by-sequencing for crossover localization and fine-scale genetic mapping. G3-GENES GENOMES GENETICS 2015; 5:385-98. [PMID: 25585881 PMCID: PMC4349092 DOI: 10.1534/g3.114.016501] [Citation(s) in RCA: 78] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The reshuffling of existing genetic variation during meiosis is important both during evolution and in breeding. The reassortment of genetic variants relies on the formation of crossovers (COs) between homologous chromosomes. The pattern of genome-wide CO distributions can be rapidly and precisely established by the short-read sequencing of individuals from F2 populations, which in turn are useful for quantitative trait locus (QTL) mapping. Although sequencing costs have decreased precipitously in recent years, the costs of library preparation for hundreds of individuals have remained high. To enable rapid and inexpensive CO detection and QTL mapping using low-coverage whole-genome sequencing of large mapping populations, we have developed a new method for library preparation along with Trained Individual GenomE Reconstruction, a probabilistic method for genotype and CO predictions for recombinant individuals. In an example case with hundreds of F2 individuals from two Arabidopsis thaliana accessions, we resolved most CO breakpoints to within 2 kb and reduced a major flowering time QTL to a 9-kb interval. In addition, an extended region of unusually low recombination revealed a 1.8-Mb inversion polymorphism on the long arm of chromosome 4. We observed no significant differences in the frequency and distribution of COs between F2 individuals with and without a functional copy of the DNA helicase gene RECQ4A. In summary, we present a new, cost-efficient method for large-scale, high-precision genotyping-by-sequencing.
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169
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Singh G, Dal Grande F, Werth S, Scheidegger C. Long-term consequences of disturbances on reproductive strategies of the rare epiphytic lichen Lobaria pulmonaria: clonality a gift and a curse. FEMS Microbiol Ecol 2014; 91:1-11. [DOI: 10.1093/femsec/fiu009] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
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170
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Termite queens close the sperm gates of eggs to switch from sexual to asexual reproduction. Proc Natl Acad Sci U S A 2014; 111:17212-7. [PMID: 25404335 DOI: 10.1073/pnas.1412481111] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Males and females are in conflict over genetic transmission in the evolution of parthenogenesis, because it enhances female reproductive output but deprives the males' genetic contribution. For males, any trait that coerces females into sexual reproduction should increase their fitness. However, in the termite Reticulitermes speratus, queens produce their replacements (neotenic queens) parthenogenetically while using normal sexual reproduction to produce other colony members. Here, we show that termite queens produce parthenogenetic offspring in the presence of kings by closing the micropyles (sperm gates; i.e., openings for sperm entry) of their eggs. Our field survey showed that termite eggs show large variation in numbers of micropyles, with some having none. Microsatellite analysis showed that embryos of micropyleless eggs develop parthenogenetically, whereas those of eggs with micropyles are fertilized and develop sexually. Surveys of eggs among queens of different age groups showed that queens begin to lay micropyleless eggs when they are older and thus, need to produce their replacements parthenogenetically. In addition, we found clear seasonality in new neotenic queen differentiation and micropyleless egg production. This micropyle-dependent parthenogenesis is the first identification, to our knowledge, of the mechanism through which females control egg fertilization over time in diploid animals, implying a novel route of the evolution of parthenogenesis in favor of female interests without interference from males.
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171
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Abstract
Algorithms, perhaps together with Moore's law, compose the engine of the information technology revolution, whereas complexity--the antithesis of algorithms--is one of the deepest realms of mathematical investigation. After introducing the basic concepts of algorithms and complexity, and the fundamental complexity classes P (polynomial time) and NP (nondeterministic polynomial time, or search problems), we discuss briefly the P vs. NP problem. We then focus on certain classes between P and NP which capture important phenomena in the social and life sciences, namely the Nash equlibrium and other equilibria in economics and game theory, and certain processes in population genetics and evolution. Finally, an algorithm known as multiplicative weights update (MWU) provides an algorithmic interpretation of the evolution of allele frequencies in a population under sex and weak selection. All three of these equivalences are rife with domain-specific implications: The concept of Nash equilibrium may be less universal--and therefore less compelling--than has been presumed; selection on gene interactions may entail the maintenance of genetic variation for longer periods than selection on single alleles predicts; whereas MWU can be shown to maximize, for each gene, a convex combination of the gene's cumulative fitness in the population and the entropy of the allele distribution, an insight that may be pertinent to the maintenance of variation in evolution.
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172
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Tao L, Cao C, Liang W, Guan G, Zhang Q, Nobile CJ, Huang G. White cells facilitate opposite- and same-sex mating of opaque cells in Candida albicans. PLoS Genet 2014; 10:e1004737. [PMID: 25329547 PMCID: PMC4199524 DOI: 10.1371/journal.pgen.1004737] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2014] [Accepted: 09/08/2014] [Indexed: 11/19/2022] Open
Abstract
Modes of sexual reproduction in eukaryotic organisms are extremely diverse. The human fungal pathogen Candida albicans undergoes a phenotypic switch from the white to the opaque phase in order to become mating-competent. In this study, we report that functionally- and morphologically-differentiated white and opaque cells show a coordinated behavior during mating. Although white cells are mating-incompetent, they can produce sexual pheromones when treated with pheromones of the opposite mating type or by physically interacting with opaque cells of the opposite mating type. In a co-culture system, pheromones released by white cells induce opaque cells to form mating projections, and facilitate both opposite- and same-sex mating of opaque cells. Deletion of genes encoding the pheromone precursor proteins and inactivation of the pheromone response signaling pathway (Ste2-MAPK-Cph1) impair the promoting role of white cells (MTLa) in the sexual mating of opaque cells. White and opaque cells communicate via a paracrine pheromone signaling system, creating an environment conducive to sexual mating. This coordination between the two different cell types may be a trade-off strategy between sexual and asexual lifestyles in C. albicans. In eukaryotic organisms, cells often undergo differentiation into distinct cell types in order to fulfill specialized roles. To achieve a certain function, different cell types may behave coordinately to complete a task that they may otherwise be incapable of completing independently. The human fungal pathogen Candida albicans can exist as two functionally and morphologically distinct cell types: white and opaque. The white cell type is thought to be the default state and may be the majority cell population in nature. However, only the minority opaque cells are mating-competent. In this study, we report that white and opaque cells show a coordinated behavior in the process of mating. When in the presence of opaque cells with an opposite mating type, white cells release sexual pheromones, and thus create an environment conducive for both opposite- and same-sex mating of opaque cells. The two cell types communicate via a paracrine pheromone signaling system. We propose that this communal coordination between white and opaque cells may not only support the fungus to be a successful commensal and pathogen in the host, but may also increase the fitness of the fungus during evolution over time.
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Affiliation(s)
- Li Tao
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Chengjun Cao
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Weihong Liang
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Guobo Guan
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Qiuyu Zhang
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Clarissa J. Nobile
- Department of Molecular and Cell Biology, School of Natural Sciences, University of California, Merced, Merced, California, United States of America
| | - Guanghua Huang
- State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
- * E-mail:
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173
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Ramírez JD, Llewellyn MS. Reproductive clonality in protozoan pathogens--truth or artefact? Mol Ecol 2014; 23:4195-202. [PMID: 25060834 DOI: 10.1111/mec.12872] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Revised: 07/13/2014] [Accepted: 07/17/2014] [Indexed: 02/06/2023]
Abstract
The debate around the frequency and importance of genetic exchange in parasitic protozoa is now several decades old. Recently, fresh assertions have been made that predominant clonal evolution explains the population structures of several key protozoan pathogens. Here, we present an alternative perspective. On the assumption that much apparent clonality may be an artefact of inadequate sampling and study design, we review current research to define why sex might be so difficult to detect in protozoan parasite populations. In doing so, we contrast laboratory models of genetic exchange in parasitic protozoa with natural patterns of genetic diversity and consider the fitness advantage of sex at different evolutionary scales. We discuss approaches to improve the accuracy of efforts to characterize genetic exchange in the field. We also examine the implications of the first population genomic studies for the debate around sex and clonality in parasitic protozoa and discuss caveats for the future.
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Affiliation(s)
- Juan David Ramírez
- Unidad Clinico-Molecular de Enfermedades Infecciosas (UCMEI), Facultad de Ciencias Naturales y Matemáticas, Universidad del Rosario, Carrera 24 No. 63C-69, Bogotá, Colombia
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Lovell JT, Grogan K, Sharbel TF, McKay JK. Mating system and environmental variation drive patterns of adaptation inBoechera spatifolia(Brassicaceae). Mol Ecol 2014; 23:4486-97. [DOI: 10.1111/mec.12879] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Revised: 07/22/2014] [Accepted: 07/28/2014] [Indexed: 12/27/2022]
Affiliation(s)
- John T. Lovell
- Graduate Degree Program in Ecology; Department of BioAgricultural Sciences and Pest Management; Colorado State University; Fort Collins CO 80523-1177 USA
- Apomixis Research Group; Institute for Plant Genetics and Crop Plant Improvement (IPK); Gatersleben D-06466 Germany
| | - Kelsi Grogan
- Graduate Degree Program in Ecology; Department of BioAgricultural Sciences and Pest Management; Colorado State University; Fort Collins CO 80523-1177 USA
| | - Timothy F. Sharbel
- Apomixis Research Group; Institute for Plant Genetics and Crop Plant Improvement (IPK); Gatersleben D-06466 Germany
| | - John K. McKay
- Graduate Degree Program in Ecology; Department of BioAgricultural Sciences and Pest Management; Colorado State University; Fort Collins CO 80523-1177 USA
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175
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Arnaud-Haond S, Moalic Y, Barnabé C, Ayala FJ, Tibayrenc M. Discriminating micropathogen lineages and their reticulate evolution through graph theory-based network analysis: the case of Trypanosoma cruzi, the agent of Chagas disease. PLoS One 2014; 9:e103213. [PMID: 25148574 PMCID: PMC4141739 DOI: 10.1371/journal.pone.0103213] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Accepted: 06/28/2014] [Indexed: 12/02/2022] Open
Abstract
Micropathogens (viruses, bacteria, fungi, parasitic protozoa) share a common trait, which is partial clonality, with wide variance in the respective influence of clonality and sexual recombination on the dynamics and evolution of taxa. The discrimination of distinct lineages and the reconstruction of their phylogenetic history are key information to infer their biomedical properties. However, the phylogenetic picture is often clouded by occasional events of recombination across divergent lineages, limiting the relevance of classical phylogenetic analysis and dichotomic trees. We have applied a network analysis based on graph theory to illustrate the relationships among genotypes of Trypanosoma cruzi, the parasitic protozoan responsible for Chagas disease, to identify major lineages and to unravel their past history of divergence and possible recombination events. At the scale of T. cruzi subspecific diversity, graph theory-based networks applied to 22 isoenzyme loci (262 distinct Multi-Locus-Enzyme-Electrophoresis -MLEE) and 19 microsatellite loci (66 Multi-Locus-Genotypes -MLG) fully confirms the high clustering of genotypes into major lineages or "near-clades". The release of the dichotomic constraint associated with phylogenetic reconstruction usually applied to Multilocus data allows identifying putative hybrids and their parental lineages. Reticulate topology suggests a slightly different history for some of the main "near-clades", and a possibly more complex origin for the putative hybrids than hitherto proposed. Finally the sub-network of the near-clade T. cruzi I (28 MLG) shows a clustering subdivision into three differentiated lesser near-clades ("Russian doll pattern"), which confirms the hypothesis recently proposed by other investigators. The present study broadens and clarifies the hypotheses previously obtained from classical markers on the same sets of data, which demonstrates the added value of this approach. This underlines the potential of graph theory-based network analysis for describing the nature and relationships of major pathogens, thereby opening stimulating prospects to unravel the organization, dynamics and history of major micropathogen lineages.
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Affiliation(s)
- Sophie Arnaud-Haond
- IFREMER (Institut Français de Recherche pour l'Exploitation de la Mer) - Département Ecosystèmes Marins Exploités, Sète, France
| | - Yann Moalic
- IFREMER (Institut Français de Recherche pour l'Exploitation de la Mer) - Département Ecosystèmes Marins Exploités, Sète, France
| | - Christian Barnabé
- Interactions hôte-vecteur-parasite dans les maladies dues aux Trypanosomatidés, INTERTRYP (IRD-CIRAD), Montpellier, France
| | - Francisco José Ayala
- Department of Ecology and Evolutionary Biology, University of California Irvine, Irvine, California, United States of America
| | - Michel Tibayrenc
- Maladies Infectieuses et Vecteurs Ecologie, Génétique, Evolution et Contrôle, MIVEGEC (IRD 224-CNRS 5290-UM1-UM2), Montpellier, France
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176
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Diverse forms of selection in evolution and computer science. Proc Natl Acad Sci U S A 2014; 111:10398-9. [PMID: 25009183 DOI: 10.1073/pnas.1410107111] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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177
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Hee-Jeong J, Nasar Uddin A, Jong-In P, Senthil Kumar T, Hye-Ran K, Yong-Gu C, Ill-Sup N. Analysis of S-locus and expression of S-alleles of self-compatible rapid-cycling Brassica oleracea 'TO1000DH3'. Mol Biol Rep 2014; 41:6441-8. [PMID: 24969488 DOI: 10.1007/s11033-014-3526-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2013] [Accepted: 06/19/2014] [Indexed: 11/30/2022]
Abstract
Brassica oleracea is a strictly self-incompatible (SI) plant, but rapid-cycling B. oleracea 'TO1000DH3' is self-compatible (SC). Self-incompatibility in Brassicaceae is controlled by multiple alleles of the S-locus. Three S-locus genes, S-locus glycoprotein (SLG), S-locus receptor kinase (SRK) and S-locus protein 11 or S-locus cysteine-rich (SP11/SCR), have been reported to date, all of which are classified into class I and II. In this study, we investigated the molecular mechanism behind alterations of SI to SC in rapid-cycling B. olerace 'TO1000DH3'. Class I SRK were identified by genomic DNA PCR and PCR-RFLP analysis using SRK specific markers and found to be homozygous. Cloning and sequencing of class I SRK revealed a normal kinase domain without any S-domain/transmembrane domain. Moreover, S-locus sequencing analysis revealed only an SLG sequence, but no SP11/SCR. Expression analysis showed no SRK expression in the stigma, although other genes involved in the SI recognition reaction (SLG, MLPK, ARC1, THL) were found to have normal expression in the stigma. Taken together, the above results suggest that structural aberrations such as deletion of the SI recognition genes may be responsible for the breakdown of SI in rapid-cycling B. oleracea 'TO1000DH3'.
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Affiliation(s)
- Jung Hee-Jeong
- Department of Horticulture, Sunchon National University, 413 Jungangno, Suncheon, Jeonnam, 540-742, Republic of Korea
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Moradigaravand D, Kouyos R, Hinkley T, Haddad M, Petropoulos CJ, Engelstädter J, Bonhoeffer S. Recombination accelerates adaptation on a large-scale empirical fitness landscape in HIV-1. PLoS Genet 2014; 10:e1004439. [PMID: 24967626 PMCID: PMC4072600 DOI: 10.1371/journal.pgen.1004439] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Accepted: 04/30/2014] [Indexed: 01/18/2023] Open
Abstract
Recombination has the potential to facilitate adaptation. In spite of the substantial body of theory on the impact of recombination on the evolutionary dynamics of adapting populations, empirical evidence to test these theories is still scarce. We examined the effect of recombination on adaptation on a large-scale empirical fitness landscape in HIV-1 based on in vitro fitness measurements. Our results indicate that recombination substantially increases the rate of adaptation under a wide range of parameter values for population size, mutation rate and recombination rate. The accelerating effect of recombination is stronger for intermediate mutation rates but increases in a monotonic way with the recombination rates and population sizes that we examined. We also found that both fitness effects of individual mutations and epistatic fitness interactions cause recombination to accelerate adaptation. The estimated epistasis in the adapting populations is significantly negative. Our results highlight the importance of recombination in the evolution of HIV-I. One of the most challenging issues in evolutionary biology concerns the question of why most organisms exchange genetic material with each other, e.g. during sexual reproduction. Gene shuffling can create genetic diversity that facilitates adaptation to new environments, but theory shows that this effect is highly dependent on how different genes interact in determining the fitness of an organism. Using a large data set of fitness values based on HIV-1, we provide evidence that shuffling of genetic material indeed raises the level of genetic diversity, and as a result accelerates adaptation. Our results also propose genetic shuffling as a mechanism utilized by HIV to accelerate the evolution of multi-drug-resistant strains.
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Affiliation(s)
- Danesh Moradigaravand
- Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Zürich, Switzerland
- * E-mail: (DM); (SB)
| | - Roger Kouyos
- Division of Infectious Diseases and Hospital Epidemiology, University Hospital Zürich, University of Zürich, Zürich, Switzerland
| | - Trevor Hinkley
- WestCHEM, School of Chemistry, The University of Glasgow, Glasgow, Scotland, United Kingdom
| | - Mojgan Haddad
- Monogram Biosciences, South San Francisco, California, United States of America
| | | | - Jan Engelstädter
- School of Biological Sciences, The University of Queensland, Brisbane, Queensland, Australia
| | - Sebastian Bonhoeffer
- Institute of Integrative Biology, ETH Zürich, Zürich, Switzerland
- * E-mail: (DM); (SB)
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179
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Abstract
Even the most seasoned students of evolution, starting with Darwin himself, have occasionally expressed amazement that the mechanism of natural selection has produced the whole of Life as we see it around us. There is a computational way to articulate the same amazement: "What algorithm could possibly achieve all this in a mere three and a half billion years?" In this paper we propose an answer: We demonstrate that in the regime of weak selection, the standard equations of population genetics describing natural selection in the presence of sex become identical to those of a repeated game between genes played according to multiplicative weight updates (MWUA), an algorithm known in computer science to be surprisingly powerful and versatile. MWUA maximizes a tradeoff between cumulative performance and entropy, which suggests a new view on the maintenance of diversity in evolution.
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180
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Carvalho S, Chelo IM, Goy C, Teotónio H. The role of hermaphrodites in the experimental evolution of increased outcrossing rates in Caenorhabditis elegans. BMC Evol Biol 2014; 14:116. [PMID: 24891031 PMCID: PMC4055231 DOI: 10.1186/1471-2148-14-116] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2014] [Accepted: 05/21/2014] [Indexed: 01/16/2023] Open
Abstract
Background Why most organisms reproduce via outcrossing rather than selfing is a central question in evolutionary biology. It has long ago been suggested that outcrossing is favoured when it facilitates adaptation to novel environments. We have previously shown that the experimental evolution of increased outcrossing rates in populations of the male-hermaphrodite nematode Caenorhabditis elegans were correlated with the experimental evolution of increased male fitness. However, it is unknown whether outcrossing led to adaptation, and if so, which fitness components can explain the observed increase in outcrossing rates. Results Using experimental evolution in six populations with initially low standing levels of genetic diversity, we show with head-to-head competition assays that population-wide fitness improved during 100 generations. Since outcrossing rates increased during the same period, this result demonstrates that outcrossing is adaptive. We also show that there was little evolution of hermaphrodite fitness under conditions of selfing or under conditions of outcrossing with unrelated tester males. We nonetheless find a positive genetic correlation between hermaphrodite self-fitness and population-wide fitness, and a negative genetic correlation between hermaphrodite mating success and population-wide fitness. These results suggest that the several hermaphrodite traits measured are fitness components. Tradeoffs expressed in hermaphrodites, particularly noticed between self-fitness and mating success, may in turn explain their lack of change during experimental evolution. Conclusions Our findings indicate that outcrossing facilitates adaptation to novel environments. They further indicate that the experimental evolution of increased outcrossing rates depended little on hermaphrodites because of fitness tradeoffs between selfing and outcrossing. Instead, the evolution of increased outcrossing rates appears to have resulted from unhindered selection on males.
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Yin M, Gießler S, Griebel J, Wolinska J. Hybridizing Daphnia communities from ten neighbouring lakes: spatio-temporal dynamics, local processes, gene flow and invasiveness. BMC Evol Biol 2014; 14:80. [PMID: 24725969 PMCID: PMC4101843 DOI: 10.1186/1471-2148-14-80] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2013] [Accepted: 04/04/2014] [Indexed: 05/28/2023] Open
Abstract
BACKGROUND In natural communities of cyclical parthenogens, rapid response to environmental change is enabled by switching between two reproduction modes. While long periods of asexual reproduction allow some clones to outcompete others, and may result in "clonal erosion", sexual reproduction restores genetic variation in such systems. Moreover, sexual reproduction may result in the formation of interspecific hybrids. These hybrids can then reach high abundances, through asexual clonal reproduction. In the present study, we explored genetic variation in water fleas of the genus Daphnia. The focus was on the short-term dynamics within several clonal assemblages from the hybridizing Daphnia longispina complex and the impact of gene flow at small spatial scales. RESULTS Daphnia individuals belonged either to the parental species D. galeata and D. longispina, or to different hybrid classes, as identified by 15 microsatellite markers. The distribution and genotypic structure of parental species, but not hybrids, corresponded well with the geographical positions of the lakes. Within parental species, the genetic distance among populations of D. galeata was lower than among populations of D. longispina. Moreover, D. galeata dominance was associated with higher phosphorous load. Finally, there was no evidence for clonal erosion. CONCLUSIONS Our results suggest that the contemporary structure of hybridizing Daphnia communities from ten nearby lakes is influenced by colonization events from neighbouring habitats as well as by environmental factors. Unlike the parental species, however, there was little evidence for successful dispersal of hybrids, which seem to be produced locally. Finally, in contrast to temporary Daphnia populations, in which a decrease in clonal diversity was sometimes detectable over a single growing season, the high clonal diversity and lack of clonal erosion observed here might result from repeated hatching of sexually produced offspring. Overall, our study provides insights into spatio-temporal dynamics in a hybridizing Daphnia species complex in a recently established lake system, and relates genetic similarities of populations to a scenario of secondary invasion enhanced by environmental factors.
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Affiliation(s)
| | - Sabine Gießler
- Department Biologie II, Evolutionsökologie, Ludwig-Maximilians-Universität, Großhaderner Str, 2, 82152 Planegg-Martinsried, Germany.
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182
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A quantitative genetic signature of senescence in a short-lived perennial plant. Curr Biol 2014; 24:744-7. [PMID: 24631239 DOI: 10.1016/j.cub.2014.02.012] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2013] [Revised: 12/17/2013] [Accepted: 02/04/2014] [Indexed: 12/31/2022]
Abstract
The evolution of senescence (the physiological decline of organisms with age) poses an apparent paradox because it represents a failure of natural selection to increase the survival and reproductive performance of organisms. The paradox can be resolved if natural selection becomes less effective with age, because the death of postreproductive individuals should have diminished effects on Darwinian fitness [1, 2]. A substantial body of empirical work is consistent with this prediction for animals, which transmit their genes to progeny via an immortal germline. However, such evidence is still lacking in plants, which lack a germline and whose reproduction is diffuse and modular across the soma. Here, we provide experimental evidence for a genetic basis of senescence in the short-lived perennial plant Silene latifolia. Our pedigree-based analysis revealed a marked increase with age in the additive genetic variance of traits closely associated with fitness. This result thus extends to plants the quantitative genetic support for the evolutionary theory of senescence.
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183
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Otto SP. Selective maintenance of recombination between the sex chromosomes. J Evol Biol 2014; 27:1431-42. [DOI: 10.1111/jeb.12324] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2013] [Revised: 12/11/2013] [Accepted: 12/20/2013] [Indexed: 02/05/2023]
Affiliation(s)
- S. P. Otto
- Department of Zoology & Biodiversity Research Centre; University of British Columbia; Vancouver BC Canada
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184
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Characterization of genetic diversity in the nematode Pristionchus pacificus from population-scale resequencing data. Genetics 2014; 196:1153-65. [PMID: 24443445 DOI: 10.1534/genetics.113.159855] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The hermaphroditic nematode Pristionchus pacificus is an established model system for comparative studies with Caenorhabditis elegans in developmental biology, ecology, and population genetics. In this study, we present whole-genome sequencing data of 104 P. pacificus strains and the draft assembly of the obligate outcrossing sister species P. exspectatus. We characterize genetic diversity within P. pacificus and investigate the population genetic processes shaping this diversity. P. pacificus is 10 times more diverse than C. elegans and exhibits substantial population structure that allows us to probe its evolution on multiple timescales. Consistent with reduced effective recombination in this self-fertilizing species, we find haplotype blocks that span several megabases. Using the P. exspectatus genome as an outgroup, we polarized variation in P. pacificus and found a site frequency spectrum (SFS) that decays more rapidly than expected in neutral models. The SFS at putatively neutral sites is U shaped, which is a characteristic feature of pervasive linked selection. Based on the additional findings (i) that the majority of nonsynonymous variation is eliminated over timescales on the order of the separation between clades, (ii) that diversity is reduced in gene-rich regions, and (iii) that highly differentiated clades show very similar patterns of diversity, we conclude that purifying selection on many mutations with weak effects is a major force shaping genetic diversity in P. pacificus.
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185
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Abstract
Yeast prions are infectious proteins that spread exclusively by mating. The frequency of prions in the wild therefore largely reflects the rate of spread by mating counterbalanced by prion growth slowing effects in the host. We recently showed that the frequency of outcross mating is about 1% of mitotic doublings with 23–46% of total matings being outcrosses. These findings imply that even the mildest forms of the [PSI+], [URE3] and [PIN+] prions impart > 1% growth/survival detriment on their hosts. Our estimate of outcrossing suggests that Saccharomyces cerevisiae is far more sexual than previously thought and would therefore be more responsive to the adaptive effects of natural selection compared with a strictly asexual yeast. Further, given its large effective population size, a growth/survival detriment of > 1% for yeast prions should strongly select against prion-infected strains in wild populations of Saccharomyces cerevisiae.
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Affiliation(s)
- Amy C Kelly
- Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD, USA
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186
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Coexistence of sexual individuals and genetically isolated asexual counterparts in a thrips. Sci Rep 2013; 3:3286. [PMID: 24256637 PMCID: PMC3836029 DOI: 10.1038/srep03286] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2013] [Accepted: 11/04/2013] [Indexed: 11/09/2022] Open
Abstract
Sex is a paradoxical phenomenon because it is less efficient compared with asexual reproduction. To resolve this paradox we need a direct comparison between sexual and asexual forms. In many organisms, however, sexual and asexual forms do not occur in the same habitat, or at the same time. In a few cases where sexual and asexual forms are found in a single population, some (though rare) genetic exchange is usually detected between the two forms. When genetic exchange occurs a direct comparison is impossible. Here we investigate a thrips exhibiting both sexual and asexual forms (lineages) that are morphologically indistinguishable. We examine if the two forms are genetically isolated. Phylogeny based on nuclear genes confirms that the sexual and asexual lineages are genetically differentiated. Thus we demonstrate that the current system has certain advantages over existing and previously used model systems in the evolution of sexual reproduction.
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187
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Metzger JJ, Eule S. Distribution of the fittest individuals and the rate of Muller's ratchet in a model with overlapping generations. PLoS Comput Biol 2013; 9:e1003303. [PMID: 24244123 PMCID: PMC3820511 DOI: 10.1371/journal.pcbi.1003303] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Accepted: 09/10/2013] [Indexed: 11/17/2022] Open
Abstract
Muller's ratchet is a paradigmatic model for the accumulation of deleterious mutations in a population of finite size. A click of the ratchet occurs when all individuals with the least number of deleterious mutations are lost irreversibly due to a stochastic fluctuation. In spite of the simplicity of the model, a quantitative understanding of the process remains an open challenge. In contrast to previous works, we here study a Moran model of the ratchet with overlapping generations. Employing an approximation which describes the fittest individuals as one class and the rest as a second class, we obtain closed analytical expressions of the ratchet rate in the rare clicking regime. As a click in this regime is caused by a rare, large fluctuation from a metastable state, we do not resort to a diffusion approximation but apply an approximation scheme which is especially well suited to describe extinction events from metastable states. This method also allows for a derivation of expressions for the quasi-stationary distribution of the fittest class. Additionally, we confirm numerically that the formulation with overlapping generations leads to the same results as the diffusion approximation and the corresponding Wright-Fisher model with non-overlapping generations. Muller's ratchet is a paradigmatic model in population genetics which describes the fixation of a deleterious mutation in a population of finite size due to an unfortunate stochastic fluctuation. Obtaining quantitative predictions of the ratchet rate, i.e. the frequency with which such a mutation fixes, is believed to be important for understanding a broad range of effects ranging from the degeneration of the Y-chromosome to the evolution of sex as a means of avoiding the fixation of deleterious mutations. To obtain a better understanding of how Muller's ratchet operates, we have considered a model with overlapping generations, which allows for the application of methods specifically tailored for the analysis of rare stochastic fluctuations which drive the ratchet. We obtain concise and accurate results for the rate of Muller's ratchet. Additionally, we are able to predict the full distribution of the frequency of the fittest individuals, a quantity of central interest in understanding the ratchet rate and possibly experimentally much more accessible than the rate, in particular when the ratchet rate is very large.
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Affiliation(s)
- Jakob J Metzger
- Max Planck Institute for Dynamics and Self-Organization (MPIDS), Göttingen, Germany ; Institute for Nonlinear Dynamics, Department of Physics, University of Göttingen, Göttingen, Germany
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188
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Pellino M, Hojsgaard D, Schmutzer T, Scholz U, Hörandl E, Vogel H, Sharbel TF. Asexual genome evolution in the apomicticRanunculus auricomuscomplex: examining the effects of hybridization and mutation accumulation. Mol Ecol 2013; 22:5908-21. [DOI: 10.1111/mec.12533] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2012] [Revised: 08/21/2013] [Accepted: 08/26/2013] [Indexed: 10/26/2022]
Affiliation(s)
- Marco Pellino
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK); D-06466 Gatersleben Germany
| | - Diego Hojsgaard
- Department of Systematic Botany; Albrecht-von-Haller Institute for Plant Sciences; Georg-August-University of Goettingen; Untere Karspuele 2 D-37073 Goettingen Germany
| | - Thomas Schmutzer
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK); D-06466 Gatersleben Germany
| | - Uwe Scholz
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK); D-06466 Gatersleben Germany
| | - Elvira Hörandl
- Department of Systematic Botany; Albrecht-von-Haller Institute for Plant Sciences; Georg-August-University of Goettingen; Untere Karspuele 2 D-37073 Goettingen Germany
| | - Heiko Vogel
- Department of Entomology; Max Planck Institute for Chemical Ecology; D-07745 Jena Germany
| | - Timothy F. Sharbel
- Leibniz Institute of Plant Genetics and Crop Plant Research (IPK); D-06466 Gatersleben Germany
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189
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Saakian DB, Hu CK. Evolutionary advantage via common action of recombination and neutrality. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2013; 88:052717. [PMID: 24329306 DOI: 10.1103/physreve.88.052717] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2012] [Revised: 07/09/2013] [Indexed: 06/03/2023]
Abstract
We investigate evolution models with recombination and neutrality. We consider the Crow-Kimura (parallel) mutation-selection model with the neutral fitness landscape, in which there is a central peak with high fitness A, and some of 1-point mutants have the same high fitness A, while the fitness of other sequences is 0. We find that the effect of recombination and neutrality depends on the concrete version of both neutrality and recombination. We consider three versions of neutrality: (a) all the nearest neighbor sequences of the peak sequence have the same high fitness A; (b) all the l-point mutations in a piece of genome of length l≥1 are neutral; (c) the neutral sequences are randomly distributed among the nearest neighbors of the peak sequences. We also consider three versions of recombination: (I) the simple horizontal gene transfer (HGT) of one nucleotide; (II) the exchange of a piece of genome of length l, HGT-l; (III) two-point crossover recombination (2CR). For the case of (a), the 2CR gives a rather strong contribution to the mean fitness, much stronger than that of HGT for a large genome length L. For the random distribution of neutral sequences there is a critical degree of neutrality ν(c), and for μ<μ(c) and (μ(c)-μ) is not large, the 2CR suppresses the mean fitness while HGT increases it; for ν much larger than ν(c), the 2CR and HGT-l increase the mean fitness larger than that of the HGT. We also consider the recombination in the case of smooth fitness landscapes. The recombination gives some advantage in the evolutionary dynamics, where recombination distinguishes clearly the mean-field-like evolutionary factors from the fluctuation-like ones. By contrast, mutations affect the mean-field-like and fluctuation-like factors similarly. Consequently, recombination can accelerate the non-mean-field (fluctuation) type dynamics without considerably affecting the mean-field-like factors.
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Affiliation(s)
- David B Saakian
- Institute of Physics, Academia Sinica, Nankang, Taipei 11529, Taiwan and A. I. Alikhanyan National Science Laboratory (Yerevan Physics Institute) Foundation, 2 Alikhanian Brothers Street, Yerevan 375036, Armenia and Physics Division of National Center for Theoretical Sciences Taipei Branch, National Taiwan University, Taipei, Taiwan
| | - Chin-Kun Hu
- Institute of Physics, Academia Sinica, Nankang, Taipei 11529, Taiwan
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190
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Holman L, Kokko H. The evolution of genomic imprinting: costs, benefits and long-term consequences. Biol Rev Camb Philos Soc 2013; 89:568-87. [DOI: 10.1111/brv.12069] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2013] [Revised: 09/15/2013] [Accepted: 09/26/2013] [Indexed: 12/23/2022]
Affiliation(s)
- Luke Holman
- Centre of Excellence in Biological Interactions, Division of Ecology, Evolution & Genetics; Research School of Biology, Australian National University; Daley Road, Canberra Australian Capital Territory 0200 Australia
| | - Hanna Kokko
- Centre of Excellence in Biological Interactions, Division of Ecology, Evolution & Genetics; Research School of Biology, Australian National University; Daley Road, Canberra Australian Capital Territory 0200 Australia
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191
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Livnat A. Interaction-based evolution: how natural selection and nonrandom mutation work together. Biol Direct 2013; 8:24. [PMID: 24139515 PMCID: PMC4231362 DOI: 10.1186/1745-6150-8-24] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2013] [Accepted: 09/26/2013] [Indexed: 12/30/2022] Open
Abstract
BACKGROUND The modern evolutionary synthesis leaves unresolved some of the most fundamental, long-standing questions in evolutionary biology: What is the role of sex in evolution? How does complex adaptation evolve? How can selection operate effectively on genetic interactions? More recently, the molecular biology and genomics revolutions have raised a host of critical new questions, through empirical findings that the modern synthesis fails to explain: for example, the discovery of de novo genes; the immense constructive role of transposable elements in evolution; genetic variance and biochemical activity that go far beyond what traditional natural selection can maintain; perplexing cases of molecular parallelism; and more. PRESENTATION OF THE HYPOTHESIS Here I address these questions from a unified perspective, by means of a new mechanistic view of evolution that offers a novel connection between selection on the phenotype and genetic evolutionary change (while relying, like the traditional theory, on natural selection as the only source of feedback on the fit between an organism and its environment). I hypothesize that the mutation that is of relevance for the evolution of complex adaptation-while not Lamarckian, or "directed" to increase fitness-is not random, but is instead the outcome of a complex and continually evolving biological process that combines information from multiple loci into one. This allows selection on a fleeting combination of interacting alleles at different loci to have a hereditary effect according to the combination's fitness. TESTING AND IMPLICATIONS OF THE HYPOTHESIS This proposed mechanism addresses the problem of how beneficial genetic interactions can evolve under selection, and also offers an intuitive explanation for the role of sex in evolution, which focuses on sex as the generator of genetic combinations. Importantly, it also implies that genetic variation that has appeared neutral through the lens of traditional theory can actually experience selection on interactions and thus has a much greater adaptive potential than previously considered. Empirical evidence for the proposed mechanism from both molecular evolution and evolution at the organismal level is discussed, and multiple predictions are offered by which it may be tested. REVIEWERS This article was reviewed by Nigel Goldenfeld (nominated by Eugene V. Koonin), Jürgen Brosius and W. Ford Doolittle.
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Affiliation(s)
- Adi Livnat
- Department of Biological Sciences, Virginia Tech, Blacksburg, VA, 24061,
USA
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192
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High-throughput analysis of meiotic crossover frequency and interference via flow cytometry of fluorescent pollen in Arabidopsis thaliana. Nat Protoc 2013; 8:2119-34. [PMID: 24113785 DOI: 10.1038/nprot.2013.131] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
During meiosis, reciprocal exchange between homologous chromosomes occurs as a result of crossovers (COs). CO frequency varies within genomes and is subject to genetic, epigenetic and environmental control. As robust measurement of COs is limited by their low numbers, typically 1-2 per chromosome, we adapted flow cytometry for use with Arabidopsis transgenic fluorescent protein-tagged lines (FTLs) that express eCFP, dsRed or eYFP fluorescent proteins in pollen. Segregation of genetically linked transgenes encoding fluorescent proteins of distinct colors can be used to detect COs. The fluorescence of up to 80,000 pollen grains per individual plant can be measured in 10-15 min using this protocol. A key element of CO control is interference, which inhibits closely spaced COs. We describe a three-color assay for the measurement of CO frequency in adjacent intervals and calculation of CO interference. We show that this protocol can be used to detect changes in CO frequency and interference in the fancm zip4 double mutant. By enabling high-throughput measurement of CO frequency and interference, these methods will facilitate genetic dissection of meiotic recombination control.
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193
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Bobay LM, Touchon M, Rocha EPC. Manipulating or superseding host recombination functions: a dilemma that shapes phage evolvability. PLoS Genet 2013; 9:e1003825. [PMID: 24086157 PMCID: PMC3784561 DOI: 10.1371/journal.pgen.1003825] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2013] [Accepted: 08/08/2013] [Indexed: 11/18/2022] Open
Abstract
Phages, like many parasites, tend to have small genomes and may encode autonomous functions or manipulate those of their hosts'. Recombination functions are essential for phage replication and diversification. They are also nearly ubiquitous in bacteria. The E. coli genome encodes many copies of an octamer (Chi) motif that upon recognition by RecBCD favors repair of double strand breaks by homologous recombination. This might allow self from non-self discrimination because RecBCD degrades DNA lacking Chi. Bacteriophage Lambda, an E. coli parasite, lacks Chi motifs, but escapes degradation by inhibiting RecBCD and encoding its own autonomous recombination machinery. We found that only half of 275 lambdoid genomes encode recombinases, the remaining relying on the host's machinery. Unexpectedly, we found that some lambdoid phages contain extremely high numbers of Chi motifs concentrated between the phage origin of replication and the packaging site. This suggests a tight association between replication, packaging and RecBCD-mediated recombination in these phages. Indeed, phages lacking recombinases strongly over-represent Chi motifs. Conversely, phages encoding recombinases and inhibiting host recombination machinery select for the absence of Chi motifs. Host and phage recombinases use different mechanisms and the latter are more tolerant to sequence divergence. Accordingly, we show that phages encoding their own recombination machinery have more mosaic genomes resulting from recent recombination events and have more diverse gene repertoires, i.e. larger pan genomes. We discuss the costs and benefits of superseding or manipulating host recombination functions and how this decision shapes phage genome structure and evolvability. Bacterial viruses, called bacteriophages, are extremely abundant in the biosphere. They have key roles in the regulation of bacterial populations and in the diversification of bacterial genomes. Among these viruses, lambdoid phages are very abundant in enterobacteria and exchange genetic material very frequently. This latter process is thought to increase phage diversity and therefore facilitate adaptation to hosts. Recombination is also essential for the replication of many lambdoid phages. Lambdoids have been described to encode their own recombination genes and inhibit their hosts'. In this study, we show that lambdoids are split regarding their capacity to encode autonomous recombination functions and that this affects the abundance of recombination-related sequence motifs. Half of the phages encode an autonomous system and inhibit their hosts'. The trade-off between superseding and manipulating the hosts' recombination functions has important consequences. The phages encoding autonomous recombination functions have more diverse gene repertoires and recombine more frequently. Viruses, as many other parasites, have small genomes and depend on their hosts for several housekeeping functions. Hence, they often face trade-offs between supersession and manipulation of molecular machineries. Our results suggest these trade-offs may shape viral gene repertoires, their sequence composition and even influence their evolvability.
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Affiliation(s)
- Louis-Marie Bobay
- Microbial Evolutionary Genomics, Institut Pasteur, Paris, France
- CNRS, UMR3525, Paris, France
- Université Pierre et Marie Curie, Cellule Pasteur UPMC, Paris, France
- * E-mail:
| | - Marie Touchon
- Microbial Evolutionary Genomics, Institut Pasteur, Paris, France
- CNRS, UMR3525, Paris, France
| | - Eduardo P. C. Rocha
- Microbial Evolutionary Genomics, Institut Pasteur, Paris, France
- CNRS, UMR3525, Paris, France
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194
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Tucker AE, Ackerman MS, Eads BD, Xu S, Lynch M. Population-genomic insights into the evolutionary origin and fate of obligately asexual Daphnia pulex. Proc Natl Acad Sci U S A 2013; 110:15740-5. [PMID: 23959868 PMCID: PMC3785735 DOI: 10.1073/pnas.1313388110] [Citation(s) in RCA: 105] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Despite much theoretical work, the molecular-genetic causes and evolutionary consequences of asexuality remain largely undetermined. Asexual animal species are rare, evolutionarily short-lived, and thought to suffer mutational meltdown as a result of lack of recombination. Whole-genome analysis of 11 sexual and 11 asexual genotypes of Daphnia pulex indicates that current asexual lineages are in fact very young, exhibit no signs of purifying selection against accumulating mutations, and have extremely high rates of gene conversion and deletion. The reconstruction of chromosomal haplotypes in regions containing SNP markers associated with asexuality (chromosomes VIII and IX) indicates that introgression from a sister species, Daphnia pulicaria, underlies the origin of the asexual phenotype. Silent-site divergence of the shared chromosomal haplotypes of asexuals indicates that the spread of asexuality is as recent as 1,250 y, although the origin of the meiosis-suppressing element or elements could be substantially older. In addition, using previous estimates of the gene conversion rate from Daphnia mutation accumulation lines, we are able to age each asexual lineage. Although asexual lineages originate from wide crosses that introduce elevated individual heterozygosities on clone foundation, they also appear to be constrained by the inbreeding-like effect of loss of heterozygosity that accrues as gene conversion and hemizygous deletion expose preexisting recessive deleterious alleles of asexuals, limiting their evolutionary longevity. Our study implies that the buildup of newly introduced deleterious mutations (i.e., Muller's ratchet) may not be the dominant force imperiling nonrecombining populations of D. pulex, as previously proposed.
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Affiliation(s)
| | | | - Brian D. Eads
- Department of Biology, Indiana University, Bloomington, IN 47405
| | - Sen Xu
- Department of Biology, Indiana University, Bloomington, IN 47405
| | - Michael Lynch
- Department of Biology, Indiana University, Bloomington, IN 47405
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195
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Asexual Daphnia genomes expose something old, new, borrowed, and blue. Proc Natl Acad Sci U S A 2013; 110:15518-9. [PMID: 24062444 DOI: 10.1073/pnas.1314088110] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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196
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Relative effects of segregation and recombination on the evolution of sex in finite diploid populations. Heredity (Edinb) 2013; 111:505-12. [PMID: 23900397 DOI: 10.1038/hdy.2013.72] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2012] [Revised: 05/19/2013] [Accepted: 06/18/2013] [Indexed: 11/08/2022] Open
Abstract
The mechanism of reproducing more viable offspring in response to selection is a major factor influencing the advantages of sex. In diploids, sexual reproduction combines genotype by recombination and segregation. Theoretical studies of sexual reproduction have investigated the advantage of recombination in haploids. However, the potential advantage of segregation in diploids is less studied. This study aimed to quantify the relative contribution of recombination and segregation to the evolution of sex in finite diploids by using multilocus simulations. The mean fitness of a sexually or asexually reproduced population was calculated to describe the long-term effects of sex. The evolutionary fate of a sex or recombination modifier was also monitored to investigate the short-term effects of sex. Two different scenarios of mutations were considered: (1) only deleterious mutations were present and (2) a combination of deleterious and beneficial mutations. Results showed that the combined effects of segregation and recombination strongly contributed to the evolution of sex in diploids. If deleterious mutations were only present, segregation efficiently slowed down the speed of Muller's ratchet. As the recombination level was increased, the accumulation of deleterious mutations was totally inhibited and recombination substantially contributed to the evolution of sex. The presence of beneficial mutations evidently increased the fixation rate of a recombination modifier. We also observed that the twofold cost of sex was easily to overcome in diploids if a sex modifier caused a moderate frequency of sex.
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197
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Rey O, Facon B, Foucaud J, Loiseau A, Estoup A. Androgenesis is a maternal trait in the invasive ant Wasmannia auropunctata. Proc Biol Sci 2013; 280:20131181. [PMID: 23864597 DOI: 10.1098/rspb.2013.1181] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Androgenesis is the production of an offspring containing exclusively the nuclear genome of the fathering male via the maternal eggs. This unusual mating system is generally considered a male trait, giving to androgenetic males a substantial fitness advantage over their sexually reproducing relatives. We here provide the first empirical study of the evolutionary outcomes of androgenesis in a haplo-diploid organism: the invasive ant Wasmannia auropunctata. Some of the populations of this species have a classical haplo-diploid sexual mating system. In other populations, females and males are produced through parthenogenesis and androgenesis, respectively, whereas workers are produced sexually. We conducted laboratory reciprocal-cross experiments with reproductive individuals from both types of populations and analysed their progenies with genetic markers, to determine the respective contribution of males and females to the production of androgenetic males. We found that androgenesis was a parthenogenetic female trait. A population genetic study conducted in natura confirmed the parthenogenetic female origin of androgenesis, with the identification of introgression events of sexual male genotypes into androgenetic/parthenogenetic lineages. We argue that by producing males via androgenesis, parthenogenetic queen lineages may increase and/or maintain their adaptive potential, while maintaining the integrity of their own genome, by occasionally acquiring new male genetic material and avoiding inbreeding depression within the sexually produced worker cast.
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198
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van der Nest MA, Steenkamp ET, Wilken MP, Stenlid J, Wingfield MJ, Wingfield BD, Slippers B. Mutualism and asexual reproduction influence recognition genes in a fungal symbiont. Fungal Biol 2013; 117:439-50. [PMID: 23809654 DOI: 10.1016/j.funbio.2013.05.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2012] [Revised: 04/23/2013] [Accepted: 05/01/2013] [Indexed: 11/20/2022]
Abstract
Mutualism between microbes and insects is common and alignment of the reproductive interests of microbial symbionts with this lifestyle typically involves clonal reproduction and vertical transmission by insect partners. Here the Amylostereum fungus-Sirex woodwasp mutualism was used to consider whether their prolonged association and predominance of asexuality have affected the mating system of the fungal partner. Nucleotide information for the pheromone receptor gene rab1, as well as the translation elongation factor 1α gene and ribosomal RNA internal transcribed spacer region were utilized. The identification of rab1 alleles in Amylostereum chailletii and Amylostereum areolatum populations revealed that this gene is more polymorphic than the other two regions, although the diversity of all three regions was lower than what has been observed in free-living Agaricomycetes. Our data suggest that suppressed recombination might be implicated in the diversification of rab1, while no evidence of balancing selection was detected. We also detected positive selection at only two codons, suggesting that purifying selection is important for the evolution of rab1. The symbiotic relationship with their insect partners has therefore influenced the diversity of this gene and influenced the manner in which selection drives and maintains this diversity in A. areolatum and A. chailletii.
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MESH Headings
- Animals
- Basidiomycota/genetics
- Basidiomycota/physiology
- Cluster Analysis
- DNA, Fungal/chemistry
- DNA, Fungal/genetics
- DNA, Ribosomal Spacer/chemistry
- DNA, Ribosomal Spacer/genetics
- Genes, Mating Type, Fungal
- Hymenoptera/microbiology
- Molecular Sequence Data
- Peptide Elongation Factor 1/genetics
- Polymorphism, Genetic
- Receptors, Pheromone/genetics
- Recombination, Genetic
- Sequence Analysis, DNA
- Symbiosis
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Affiliation(s)
- Magriet A van der Nest
- Department of Genetics, Forestry and Agricultural Biotechnology Institute-FABI, University of Pretoria, Pretoria 0002, South Africa
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199
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de Vienne DM, Giraud T, Gouyon PH. Lineage Selection and the Maintenance of Sex. PLoS One 2013; 8:e66906. [PMID: 23825582 PMCID: PMC3688966 DOI: 10.1371/journal.pone.0066906] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2013] [Accepted: 05/12/2013] [Indexed: 02/04/2023] Open
Abstract
Sex predominates in eukaryotes, despite its short-term disadvantage when compared to asexuality. Myriad models have suggested that short-term advantages of sex may be sufficient to counterbalance its twofold costs. However, despite decades of experimental work seeking such evidence, no evolutionary mechanism has yet achieved broad recognition as explanation for the maintenance of sex. We explore here, through lineage-selection models, the conditions favouring the maintenance of sex. In the first model, we allowed the rate of transition to asexuality to evolve, to determine whether lineage selection favoured species with the strongest constraints preventing the loss of sex. In the second model, we simulated more explicitly the mechanisms underlying the higher extinction rates of asexual lineages than of their sexual counterparts. We linked extinction rates to the ecological and/or genetic features of lineages, thereby providing a formalisation of the only figure included in Darwin's "The origin of species". Our results reinforce the view that the long-term advantages of sex and lineage selection may provide the most satisfactory explanations for the maintenance of sex in eukaryotes, which is still poorly recognized, and provide figures and a simulation website for training and educational purposes. Short-term benefits may play a role, but it is also essential to take into account the selection of lineages for a thorough understanding of the maintenance of sex.
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Affiliation(s)
- Damien M. de Vienne
- Bionformatics and Genomics Programme, Center for Genomic Regulation (CRG), Barcelona, Spain
- Bionformatics and Genomics Programme, University Pompeu Fabra (UPF), Barcelona, Spain
| | - Tatiana Giraud
- Ecologie, Systématique et Evolution, CNRS UMR 8079, Orsay, France
- Ecologie, Systématique et Evolution, Université Paris-Sud, Orsay, France
| | - Pierre-Henri Gouyon
- Département Systématique et Evolution, Origine, Structure, Evolution de la Biodiversité, UMR 7205 CNRS-MNHN, Muséum National d'Histoire Naturelle, Paris, France
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200
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Leushkin EV, Bazykin GA. Short indels are subject to insertion-biased gene conversion. Evolution 2013; 67:2604-13. [PMID: 24033170 DOI: 10.1111/evo.12129] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2013] [Accepted: 04/05/2013] [Indexed: 11/29/2022]
Abstract
Recombination between homologous loci is accompanied by formation of heteroduplexes. Repairing mismatches in heteroduplexes often leads to single nucleotide substitutions in a process known as gene conversion. Gene conversion was shown to be GC-biased in different organisms; that is, a W(A or T)→S(G or C) substitution is more likely in this process than a S→W substitution. Here, we show that the insertion/deletion ratio for short noncoding indels that reach fixation between species is positively correlated with the recombination rate in Drosophila melanogaster, Homo sapiens, and Saccharomyces cerevisiae. This correlation is both due to an increase of the fixation rate of insertions and decrease of the fixation rate of deletions in regions of high recombination. Whole-genome data on indel polymorphism and divergence in D. melanogaster rule out mutation biases and selection as the cause of this trend, pointing to insertion-biased gene conversion as the most likely explanation. The bias toward insertions is the strongest for single-nucleotide indels, and decreases with indel length. In regions of high recombination rate this bias leads to an up to ∼5-fold excess of fixed short insertions over deletions, and substantially affects the evolution of DNA segments.
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Affiliation(s)
- Evgeny V Leushkin
- Department of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Leninskye Gory 1-73, Moscow, 119992, Russia; Institute for Information Transmission Problems of the Russian Academy of Sciences (Kharkevich Institute), Bolshoi Karetny pereulok, 19, Moscow, 127994, Russia.
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