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de Jong MJ, van Oosterhout C, Hoelzel AR, Janke A. Moderating the neutralist-selectionist debate: exactly which propositions are we debating, and which arguments are valid? Biol Rev Camb Philos Soc 2024; 99:23-55. [PMID: 37621151 DOI: 10.1111/brv.13010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2022] [Revised: 08/04/2023] [Accepted: 08/07/2023] [Indexed: 08/26/2023]
Abstract
Half a century after its foundation, the neutral theory of molecular evolution continues to attract controversy. The debate has been hampered by the coexistence of different interpretations of the core proposition of the neutral theory, the 'neutral mutation-random drift' hypothesis. In this review, we trace the origins of these ambiguities and suggest potential solutions. We highlight the difference between the original, the revised and the nearly neutral hypothesis, and re-emphasise that none of them equates to the null hypothesis of strict neutrality. We distinguish the neutral hypothesis of protein evolution, the main focus of the ongoing debate, from the neutral hypotheses of genomic and functional DNA evolution, which for many species are generally accepted. We advocate a further distinction between a narrow and an extended neutral hypothesis (of which the latter posits that random non-conservative amino acid substitutions can cause non-ecological phenotypic divergence), and we discuss the implications for evolutionary biology beyond the domain of molecular evolution. We furthermore point out that the debate has widened from its initial focus on point mutations, and also concerns the fitness effects of large-scale mutations, which can alter the dosage of genes and regulatory sequences. We evaluate the validity of neutralist and selectionist arguments and find that the tested predictions, apart from being sensitive to violation of underlying assumptions, are often derived from the null hypothesis of strict neutrality, or equally consistent with the opposing selectionist hypothesis, except when assuming molecular panselectionism. Our review aims to facilitate a constructive neutralist-selectionist debate, and thereby to contribute to answering a key question of evolutionary biology: what proportions of amino acid and nucleotide substitutions and polymorphisms are adaptive?
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Affiliation(s)
- Menno J de Jong
- Senckenberg Biodiversity and Climate Research Institute (SBiK-F), Georg-Voigt-Strasse 14-16, Frankfurt am Main, 60325, Germany
| | - Cock van Oosterhout
- Centre for Ecology, Evolution and Conservation, University of East Anglia, Norwich Research Park, Norwich, NR4 7TJ, UK
| | - A Rus Hoelzel
- Department of Biosciences, Durham University, South Road, Durham, DH1 3LE, UK
| | - Axel Janke
- Senckenberg Biodiversity and Climate Research Institute (SBiK-F), Georg-Voigt-Strasse 14-16, Frankfurt am Main, 60325, Germany
- Institute for Ecology, Evolution and Diversity, Goethe University, Max-von-Laue-Strasse 9, Frankfurt am Main, 60438, Germany
- LOEWE-Centre for Translational Biodiversity Genomics (TBG), Senckenberg Nature Research Society, Georg-Voigt-Straße 14-16, Frankfurt am Main, 60325, Germany
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2
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Chen Q, Yang H, Feng X, Chen Q, Shi S, Wu CI, He Z. Two decades of suspect evidence for adaptive molecular evolution – Negative selection confounding positive selection signals. Natl Sci Rev 2021; 9:nwab217. [PMID: 35663241 PMCID: PMC9154339 DOI: 10.1093/nsr/nwab217] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Accepted: 11/21/2021] [Indexed: 11/21/2022] Open
Abstract
There has been a large literature in the last two decades affirming adaptive DNA sequence evolution between species. The main lines of evidence are from (i) the McDonald-Kreitman (MK) test, which compares divergence and polymorphism data, and (ii) the phylogenetic analysis by maximum likelihood (PAML) test, which analyzes multispecies divergence data. Here, we apply these two tests concurrently to genomic data of Drosophila and Arabidopsis. To our surprise, the >100 genes identified by the two tests do not overlap beyond random expectation. Because the non-concordance could be due to low powers leading to high false negatives, we merge every 20–30 genes into a ‘supergene’. At the supergene level, the power of detection is large but the calls still do not overlap. We rule out methodological reasons for the non-concordance. In particular, extensive simulations fail to find scenarios whereby positive selection can only be detected by either MK or PAML, but not both. Since molecular evolution is governed by positive and negative selection concurrently, a fundamental assumption for estimating one of these (say, positive selection) is that the other is constant. However, in a broad survey of primates, birds, Drosophila and Arabidopsis, we found that negative selection rarely stays constant for long in evolution. As a consequence, the variation in negative selection is often misconstrued as a signal of positive selection. In conclusion, MK, PAML and any method that examines genomic sequence evolution has to explicitly address the variation in negative selection before estimating positive selection. In a companion study, we propose a possible path forward in two stages—first, by mapping out the changes in negative selection and then using this map to estimate positive selection. For now, the large literature on positive selection between species has to await reassessment.
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Affiliation(s)
- Qipian Chen
- State Key Laboratory of Biocontrol, Guangdong Key Lab of Plant Resources, School of Life Sciences, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Sun Yat-sen University, Guangzhou, China
| | - Hao Yang
- State Key Laboratory of Biocontrol, Guangdong Key Lab of Plant Resources, School of Life Sciences, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Sun Yat-sen University, Guangzhou, China
| | - Xiao Feng
- State Key Laboratory of Biocontrol, Guangdong Key Lab of Plant Resources, School of Life Sciences, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Sun Yat-sen University, Guangzhou, China
| | - Qingjian Chen
- State Key Laboratory of Biocontrol, Guangdong Key Lab of Plant Resources, School of Life Sciences, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Sun Yat-sen University, Guangzhou, China
| | - Suhua Shi
- State Key Laboratory of Biocontrol, Guangdong Key Lab of Plant Resources, School of Life Sciences, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Sun Yat-sen University, Guangzhou, China
| | - Chung-I Wu
- State Key Laboratory of Biocontrol, Guangdong Key Lab of Plant Resources, School of Life Sciences, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Sun Yat-sen University, Guangzhou, China
| | - Ziwen He
- State Key Laboratory of Biocontrol, Guangdong Key Lab of Plant Resources, School of Life Sciences, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Sun Yat-sen University, Guangzhou, China
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3
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He Z, Xu S, Zhang Z, Guo W, Lyu H, Zhong C, Boufford DE, Duke NC, Shi S. Convergent adaptation of the genomes of woody plants at the land-sea interface. Natl Sci Rev 2020; 7:978-993. [PMID: 34692119 PMCID: PMC8289059 DOI: 10.1093/nsr/nwaa027] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Revised: 01/30/2020] [Accepted: 02/09/2020] [Indexed: 01/19/2023] Open
Abstract
Sequencing multiple species that share the same ecological niche may be a new frontier for genomic studies. While such studies should shed light on molecular convergence, genomic-level analyses have been unsuccessful, due mainly to the absence of empirical controls. Woody plant species that colonized the global tropical coasts, collectively referred to as mangroves, are ideal for convergence studies. Here, we sequenced the genomes/transcriptomes of 16 species belonging in three major mangrove clades. To detect convergence in a large phylogeny, a CCS+ model is implemented, extending the more limited CCS method (convergence at conservative sites). Using the empirical control for reference, the CCS+ model reduces the noises drastically, thus permitting the identification of 73 convergent genes with P true (probability of true convergence) > 0.9. Products of the convergent genes tend to be on the plasma membrane associated with salinity tolerance. Importantly, convergence is more often manifested at a higher level than at amino-acid (AA) sites. Relative to >50 plant species, mangroves strongly prefer 4 AAs and avoid 5 others across the genome. AA substitutions between mangrove species strongly reflect these tendencies. In conclusion, the selection of taxa, the number of species and, in particular, the empirical control are all crucial for detecting genome-wide convergence. We believe this large study of mangroves is the first successful attempt at detecting genome-wide site convergence.
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Affiliation(s)
- Ziwen He
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Shaohua Xu
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Zhang Zhang
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Wuxia Guo
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Haomin Lyu
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Cairong Zhong
- Hainan Dongzhai Harbor National Nature Reserve Administration, Haikou 571129, China
| | | | - Norman C Duke
- Centre for Tropical Water and Aquatic Ecosystem Research, James Cook University, Townsville, QLD 4811, Australia
| | | | - Suhua Shi
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
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4
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Chen Q, Lan A, Shen X, Wu CI. Molecular Evolution in Small Steps under Prevailing Negative Selection: A Nearly Universal Rule of Codon Substitution. Genome Biol Evol 2020; 11:2702-2712. [PMID: 31504473 PMCID: PMC6777424 DOI: 10.1093/gbe/evz192] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/28/2019] [Indexed: 12/16/2022] Open
Abstract
The widely accepted view that evolution proceeds in small steps is based on two premises: 1) negative selection acts strongly against large differences and 2) positive selection favors small-step changes. The two premises are not biologically connected and should be evaluated separately. We now extend a previous approach to studying codon evolution in the entire genome. Codon substitution rate is a function of the physicochemical distance between amino acids (AAs), equated with the step size of evolution. Between nine pairs of closely related species of plants, invertebrates, and vertebrates, the evolutionary rate is strongly and negatively correlated with a set of AA distances (ΔU, scaled to [0, 1]). ΔU, a composite measure of evolutionary rates across diverse taxa, is influenced by almost all of the 48 physicochemical properties used here. The new analyses reveal a crucial trend hidden from previous studies: ΔU is strongly correlated with the evolutionary rate (R2 > 0.8) only when the genes are predominantly under negative selection. Because most genes in most taxa are strongly constrained by negative selection, ΔU has indeed appeared to be a nearly universal measure of codon evolution. In conclusion, molecular evolution at the codon level generally takes small steps due to the prevailing negative selection. Whether positive selection may, or may not, follow the small-step rule is addressed in a companion study.
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Affiliation(s)
- Qingjian Chen
- State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Ao Lan
- State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Xu Shen
- State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China
| | - Chung-I Wu
- State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China.,CAS Key Laboratory of Genomic and Precision Medicine, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing, China.,Department of Ecology and Evolution, University of Chicago
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5
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Chen Q, He Z, Lan A, Shen X, Wen H, Wu CI. Molecular Evolution in Large Steps-Codon Substitutions under Positive Selection. Mol Biol Evol 2020; 36:1862-1873. [PMID: 31077325 DOI: 10.1093/molbev/msz108] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Molecular evolution is believed to proceed in small steps. The step size can be defined by a distance reflecting physico-chemical disparities between amino acid (AA) pairs that can be exchanged by single 1-bp mutations. We show that AA substitution rates are strongly and negatively correlated with this distance but only when positive selection is relatively weak. We use the McDonald and Kreitman test to separate the influences of positive and negative selection. While negative selection is indeed stronger on AA substitutions generating larger changes in chemical properties of AAs, positive selection operates by different rules. For 65 of the 75 possible pairs, positive selection is comparable in strength regardless of AA distance. However, the ten pairs under the strongest positive selection all exhibit large leaps in chemical properties. Five of the ten pairs are shared between Drosophila and Hominoids, thus hinting at a common but modest biochemical basis of adaptation across taxa. The hypothesis that adaptive changes often take large functional steps will need to be extensively tested. If validated, molecular models will need to better integrate positive and negative selection in the search for adaptive signal.
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Affiliation(s)
- Qingjian Chen
- State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, Guangzhou, China
| | - Ziwen He
- State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, Guangzhou, China
| | - Ao Lan
- State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, Guangzhou, China
| | - Xu Shen
- State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, Guangzhou, China
| | - Haijun Wen
- State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, Guangzhou, China
| | - Chung-I Wu
- State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-Sen University, Guangzhou, China.,CAS Key Laboratory of Genomic and Precision Medicine, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing, China.,Department of Ecology and Evolution, University of Chicago, Chicago, IL
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6
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Zou Z, Zhang J. Amino acid exchangeabilities vary across the tree of life. SCIENCE ADVANCES 2019; 5:eaax3124. [PMID: 31840062 PMCID: PMC6892623 DOI: 10.1126/sciadv.aax3124] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Accepted: 09/24/2019] [Indexed: 05/05/2023]
Abstract
Different amino acid pairs have drastically different relative exchangeabilities (REs), and accounting for this variation is an important and common practice in inferring phylogenies, testing selection, and predicting mutational effects, among other analyses. In all such endeavors, REs have been generally considered invariant among species; this assumption, however, has not been scrutinized. Using maximum likelihood to analyze 180 genome sequences, we estimated REs from 90 clades representing all three domains of life, and found numerous instances of substantial between-clade differences in REs. REs show more differences between orthologous proteins of different clades than unrelated proteins of the same clade, suggesting that REs are genome-wide, clade-specific features, probably a result of proteome-wide evolutionary changes in the physicochemical environments of amino acid residues. The discovery of among-clade RE variations cautions against assuming constant REs in various analyses and demonstrates a higher-than-expected complexity in mechanisms of proteome evolution.
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7
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Xu S, He Z, Zhang Z, Guo Z, Guo W, Lyu H, Li J, Yang M, Du Z, Huang Y, Zhou R, Zhong C, Boufford DE, Lerdau M, Wu CI, Duke NC, Shi S. The origin, diversification and adaptation of a major mangrove clade (Rhizophoreae) revealed by whole-genome sequencing. Natl Sci Rev 2017; 4:721-734. [PMID: 31258950 DOI: 10.1093/nsr/nwx065] [Citation(s) in RCA: 79] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Mangroves invade some very marginal habitats for woody plants-at the interface between land and sea. Since mangroves anchor tropical coastal communities globally, their origin, diversification and adaptation are of scientific significance, particularly at a time of global climate change. In this study, a combination of single-molecule long reads and the more conventional short reads are generated from Rhizophora apiculata for the de novo assembly of its genome to a near chromosome level. The longest scaffold, N50 and N90 for the R. apiculata genome, are 13.3 Mb, 5.4 Mb and 1.0 Mb, respectively. Short reads for the genomes and transcriptomes of eight related species are also generated. We find that the ancestor of Rhizophoreae experienced a whole-genome duplication ~70 Myrs ago, which is followed rather quickly by colonization and species diversification. Mangroves exhibit pan-exome modifications of amino acid (AA) usage as well as unusual AA substitutions among closely related species. The usage and substitution of AAs, unique among plants surveyed, is correlated with the rapid evolution of proteins in mangroves. A small subset of these substitutions is associated with mangroves' highly specialized traits (vivipary and red bark) thought to be adaptive in the intertidal habitats. Despite the many adaptive features, mangroves are among the least genetically diverse plants, likely the result of continual habitat turnovers caused by repeated rises and falls of sea level in the geologically recent past. Mangrove genomes thus inform about their past evolutionary success as well as portend a possibly difficult future.
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Affiliation(s)
- Shaohua Xu
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Ziwen He
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Zhang Zhang
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Zixiao Guo
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Wuxia Guo
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Haomin Lyu
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Jianfang Li
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Ming Yang
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Zhenglin Du
- Core Genomic Facility, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing 100101, China
| | - Yelin Huang
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Renchao Zhou
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
| | - Cairong Zhong
- Hainan Dongzhai Harbor National Nature Reserve, Haikou 571129, China
| | | | - Manuel Lerdau
- Departments of Environmental Sciences and of Biology, University of Virginia, Charlottesville, VA 22904-4123, USA
| | - Chung-I Wu
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China.,Core Genomic Facility, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing 100101, China.,Department of Ecology and Evolution, University of Chicago, Chicago, IL 60637, USA
| | - Norman C Duke
- Centre for Tropical Water and Aquatic Ecosystem Research, James Cook University, Townsville, QLD 4815, Australia
| | | | - Suhua Shi
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, School of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, China
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8
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Zhang Z, He Z, Xu S, Li X, Guo W, Yang Y, Zhong C, Zhou R, Shi S. Transcriptome analyses provide insights into the phylogeny and adaptive evolution of the mangrove fern genus Acrostichum. Sci Rep 2016; 6:35634. [PMID: 27782130 PMCID: PMC5080628 DOI: 10.1038/srep35634] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2016] [Accepted: 10/03/2016] [Indexed: 12/26/2022] Open
Abstract
The mangrove fern genus Acrostichum grows in the extremely unstable marine intertidal zone under harsh conditions, such as high salt concentrations, tidal rhythms and long-term climate changes. To explore the phylogenetic relationships and molecular mechanisms underlying adaptations in this genus, we sequenced the transcriptomes of two species of Acrostichum, A. aureum and A. speciosum, as well as a species in the sister genus, Ceratopteris thalictroides. We obtained 47,517, 36,420 and 60,823 unigenes for the three ferns, of which 24.39-45.63% were annotated using public databases. The estimated divergence time revealed that Acrostichum adapted to the coastal region during the late Cretaceous, whereas the two mangrove ferns from the Indo West-Pacific (IWP) area diverged more recently. Two methods (the modified branch-site model and the Kh method) were used to identify several positively selected genes, which may contribute to differential adaptation of the two Acrostichum species to different light and salt conditions. Our study provides abundant transcriptome data and new insights into the evolution and adaptations of mangrove ferns in the inhospitable intertidal zone.
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Affiliation(s)
- Zhang Zhang
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, Sun Yat-Sen University, Guangzhou, 510275, China
| | - Ziwen He
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, Sun Yat-Sen University, Guangzhou, 510275, China
| | - Shaohua Xu
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, Sun Yat-Sen University, Guangzhou, 510275, China
| | - Xinnian Li
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, Sun Yat-Sen University, Guangzhou, 510275, China
| | - Wuxia Guo
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, Sun Yat-Sen University, Guangzhou, 510275, China
| | - Yuchen Yang
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, Sun Yat-Sen University, Guangzhou, 510275, China
| | - Cairong Zhong
- Hainan Dongzhai Harbor National Nature Reserve, Haikou, 571129, China
| | - Renchao Zhou
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, Sun Yat-Sen University, Guangzhou, 510275, China
| | - Suhua Shi
- State Key Laboratory of Biocontrol, Guangdong Provincial Key Laboratory of Plant Resources, Key Laboratory of Biodiversity Dynamics and Conservation of Guangdong Higher Education Institutes, Sun Yat-Sen University, Guangzhou, 510275, China
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9
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Abstract
A pattern in which nucleotide transitions are favored several fold over transversions is common in molecular evolution. When this pattern occurs among amino acid replacements, explanations often invoke an effect of selection, on the grounds that transitions are more conservative in their effects on proteins. However, the underlying hypothesis of conservative transitions has never been tested directly. Here we assess support for this hypothesis using direct evidence: the fitness effects of mutations in actual proteins measured via individual or paired growth experiments. We assembled data from 8 published studies, ranging in size from 24 to 757 single-nucleotide mutations that change an amino acid. Every study has the statistical power to reveal significant effects of amino acid exchangeability, and most studies have the power to discern a binary conservative-vs-radical distinction. However, only one study suggests that transitions are significantly more conservative than transversions. In the combined set of 1,239 replacements (544 transitions, 695 transversions), the chance that a transition is more conservative than a transversion is 53 % (95 % confidence interval 50 to 56) compared with the null expectation of 50 %. We show that this effect is not large compared with that of most biochemical factors, and is not large enough to explain the several-fold bias observed in evolution. In short, the available data have the power to verify the “conservative transitions” hypothesis if true, but suggest instead that selection on proteins plays at best a minor role in the observed bias.
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Affiliation(s)
- Arlin Stoltzfus
- Institute for Bioscience and Biotechnology Research, Rockville, MD Genome-scale Measurements Group, National Institute of Standards and Technology, Gaithersburg, MD
| | - Ryan W Norris
- Department of Evolution, Ecology and Organismal Biology, The Ohio State University
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10
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Prediction of sites under adaptive evolution in flavin-containing monooxygenases: Selection pattern revisited. ACTA ACUST UNITED AC 2011. [DOI: 10.1007/s11434-011-4380-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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11
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Vallender EJ. Comparative genetic approaches to the evolution of human brain and behavior. Am J Hum Biol 2010; 23:53-64. [PMID: 21140466 DOI: 10.1002/ajhb.21132] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
With advances in genomic technologies, the amount of genetic data available to scientists today is vast. Genomes are now available or planned for 14 different primate species and complete resequencing of numerous human individuals from numerous populations is underway. Moreover, high-throughput deep sequencing is quickly making whole genome efforts within the reach of single laboratories allowing for unprecedented studies. Comparative genetic approaches to the identification of the underlying basis of human brain, behavior, and cognitive ability are moving to the forefront. Two approaches predominate: inter-species divergence comparisons and intra-species polymorphism studies. These methodological differences are useful for different time scales of evolution and necessarily focus on different evolutionary events in the history of primate and hominin evolution. Inter-species divergence is more useful in studying large scale primate, or hominoid, evolution whereas intra-species polymorphism can be more illuminating of recent hominin evolution. These differences in methodological utility also extend to studies of differing genetic substrates; current divergence studies focus primarily on protein evolution whereas polymorphism studies are substrate ambivalent. Some of the issues inherent in these studies can be ameliorated by current sequencing capabilities whereas others remain intractable. New avenues are also being opened that allow for the incorporation of novel substrates and approaches. In the post-genomic era, the study of human evolution, specifically as it relates to the brain, is becoming more complete focusing increasingly on the totality of the system and better conceptualizing the entirety of the genetic changes that have lead to the human phenotype today.
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Affiliation(s)
- Eric J Vallender
- New England Primate Research Center, Harvard Medical School, Southborough, Massachusetts, USA.
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12
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Zhang Z, Yu J. Modeling compositional dynamics based on GC and purine contents of protein-coding sequences. Biol Direct 2010; 5:63. [PMID: 21059261 PMCID: PMC2989939 DOI: 10.1186/1745-6150-5-63] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2010] [Accepted: 11/08/2010] [Indexed: 12/03/2022] Open
Abstract
Background Understanding the compositional dynamics of genomes and their coding sequences is of great significance in gaining clues into molecular evolution and a large number of publically-available genome sequences have allowed us to quantitatively predict deviations of empirical data from their theoretical counterparts. However, the quantification of theoretical compositional variations for a wide diversity of genomes remains a major challenge. Results To model the compositional dynamics of protein-coding sequences, we propose two simple models that take into account both mutation and selection effects, which act differently at the three codon positions, and use both GC and purine contents as compositional parameters. The two models concern the theoretical composition of nucleotides, codons, and amino acids, with no prerequisite of homologous sequences or their alignments. We evaluated the two models by quantifying theoretical compositions of a large collection of protein-coding sequences (including 46 of Archaea, 686 of Bacteria, and 826 of Eukarya), yielding consistent theoretical compositions across all the collected sequences. Conclusions We show that the compositions of nucleotides, codons, and amino acids are largely determined by both GC and purine contents and suggest that deviations of the observed from the expected compositions may reflect compositional signatures that arise from a complex interplay between mutation and selection via DNA replication and repair mechanisms. Reviewers This article was reviewed by Zhaolei Zhang (nominated by Mark Gerstein), Guruprasad Ananda (nominated by Kateryna Makova), and Daniel Haft.
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Affiliation(s)
- Zhang Zhang
- Plant Stress Genomics Research Center, Division of Chemical and Life Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
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13
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Thusberg J, Vihinen M. Pathogenic or not? And if so, then how? Studying the effects of missense mutations using bioinformatics methods. Hum Mutat 2009; 30:703-14. [PMID: 19267389 DOI: 10.1002/humu.20938] [Citation(s) in RCA: 181] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Many gene defects are relatively easy to identify experimentally, but obtaining information about the effects of sequence variations and elucidation of the detailed molecular mechanisms of genetic diseases will be among the next major efforts in mutation research. Amino acid substitutions may have diverse effects on protein structure and function; thus, a detailed analysis of the mutations is essential. Experimental study of the molecular effects of mutations is laborious, whereas useful and reliable information about the effects of amino acid substitutions can readily be obtained by theoretical methods. Experimentally defined structures and molecular modeling can be used as a basis for interpretation of the mutations. The effects of missense mutations can be analyzed even when the 3D structure of the protein has not been determined, although structure-based analyses are more reliable. Structural analyses include studies of the contacts between residues, their implication for the stability of the protein, and the effects of the introduced residues. Investigations of steric and stereochemical consequences of substitutions provide insights on the molecular fit of the introduced residue. Mutations that change the electrostatic surface potential of a protein have wide-ranging effects. Analyses of the effects of mutations on interactions with ligands and partners have been performed for elucidation of functional mutations. We have employed numerous methods for predicting the effects of amino acid substitutions. We discuss the applicability of these methods in the analysis of genes, proteins, and diseases to reveal protein structure-function relationships, which is essential to gain insights into disease genotype-phenotype correlations.
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Affiliation(s)
- Janita Thusberg
- Institute of Medical Technology, FI-33014 University of Tampere, Finland
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14
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Axelsson E, Ellegren H. Quantification of adaptive evolution of genes expressed in avian brain and the population size effect on the efficacy of selection. Mol Biol Evol 2009; 26:1073-9. [PMID: 19188264 DOI: 10.1093/molbev/msp019] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Whether protein evolution is mainly due to fixation of beneficial alleles by positive selection or to random genetic drift has remained a contentious issue over the years. Here, we use two genomewide polymorphism data sets collected from chicken populations, together with divergence data from >5,000 chicken-zebra finch gene orthologs expressed in brain, to assess the amount of adaptive evolution in protein-coding genes of birds. First, we show that estimates of the fixation index (FI, the ratio of fixed nonsynonymous-to-synonymous changes over the ratio of the corresponding polymorphisms) are highly dependent on the character of the underlying data sets. Second, by using polymorphism data from high-frequency alleles, to avoid the confounding effect of slightly deleterious mutations segregating at low frequency, we estimate that about 20% of amino acid changes have been brought to fixation through positive selection during avian evolution. This estimate is intermediate to that obtained in humans (lower) and flies as well as bacteria (higher), and is consistent with population genetics theory that stipulates a positive relationship between the efficiency of selection and the effective population size. Further, by comparing the FIs for common and all alleles, we estimate that approximately 20% of nonsynonymous variation segregating in chicken populations represent slightly deleterious mutations, which is less than in Drosophila. Overall, these results highlight the link between the effective population size and positive as well as negative selection.
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Affiliation(s)
- Erik Axelsson
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden
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15
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A history of recurrent positive selection at the toll-like receptor 5 in primates. Mol Biol Evol 2009; 26:937-49. [PMID: 19179655 DOI: 10.1093/molbev/msp018] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Many genes involved in immunity evolve rapidly. It remains unclear, however, to what extent pattern-recognition receptors (PRRs) of the innate immune system in vertebrates are subject to recurrent positive selection imposed by pathogens, as suggested by studies in Drosophila, or whether they are evolutionarily constrained. Here, we show that Toll-like receptor 5 (TLR5), a member of the Toll-like receptor family of innate immunity genes that responds to bacterial flagellin, has undergone a history of adaptive evolution in primates. We have identified specific residues that have changed multiple times, sometimes in parallel in primates, and are thus likely candidates for selection. Most of these changes map to the extracellular leucine-rich repeats involved in pathogen recognition, and some are likely to have an effect on protein function due to the radical nature of the amino acid substitutions that are involved. These findings suggest that vertebrate PRRs might show similar patterns of evolution to Drosophila PRRs, in spite of the acquisition of the more complex and specific vertebrate adaptive immune system. At shorter timescales, however, we found no evidence of adaptive evolution in either humans or chimpanzees. In fact, we found that one mutation that abolishes TLR5 function is present at high frequencies in many human populations. Patterns of variation indicate that this mutation is not young, and its high frequency suggests some functional redundancy for this PRR in humans.
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16
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Abstract
Models that explicitly account for the effect of selection on new mutations have been proposed to account for "codon bias" or the excess of "preferred" codons that results from selection for translational efficiency and/or accuracy. In principle, such models can be applied to any mutation that results in a preferred allele, but in most cases, the fitness effect of a specific mutation cannot be predicted. Here we show that it is possible to assign preferred and unpreferred states to amino acid changing mutations that occur in protein domains. We propose that mutations that lead to more common amino acids (at a given position in a domain) can be considered "preferred alleles" just as are synonymous mutations leading to codons for more abundant tRNAs. We use genome-scale polymorphism data to show that alleles for preferred amino acids in protein domains occur at higher frequencies in the population, as has been shown for preferred codons. We show that this effect is quantitative, such that there is a correlation between the shift in frequency of preferred alleles and the predicted fitness effect. As expected, we also observe a reduction in the numbers of polymorphisms and substitutions at more important positions in domains, consistent with stronger selection at those positions. We examine the derived allele frequency distribution and polymorphism to divergence ratios of preferred and unpreferred differences and find evidence for both negative and positive selections acting to maintain protein domains in the human population. Finally, we analyze a model for selection on amino acid preferences in protein domains and find that it is consistent with the quantitative effects that we observe.
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Affiliation(s)
- Alan M Moses
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, UK.
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17
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Rokas A, Carroll SB. Frequent and widespread parallel evolution of protein sequences. Mol Biol Evol 2008; 25:1943-53. [PMID: 18583353 DOI: 10.1093/molbev/msn143] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Understanding the patterns and causes of protein sequence evolution is a major challenge in evolutionary biology. One of the critical unresolved issues is the relative contribution of selection and genetic drift to the fixation of amino acid sequence differences between species. Molecular homoplasy, the independent evolution of the same amino acids at orthologous sites in different taxa, is one potential signature of selection; however, relatively little is known about its prevalence in eukaryotic proteomes. To quantify the extent and type of homoplasy among evolving proteins, we used phylogenetic methodology to analyze 8 genome-scale data matrices from clades of different evolutionary depths that span the eukaryotic tree of life. We found that the frequency of homoplastic amino acid substitutions in eukaryotic proteins was more than 2-fold higher than expected under neutral models of protein evolution. The overwhelming majority of homoplastic substitutions were parallelisms that involved the most frequently exchanged amino acids with similar physicochemical properties and that could be reached by a single-mutational step. We conclude that the role of homoplasy in shaping the protein record is much larger than generally assumed, and we suggest that its high frequency can be explained by both weak positive selection for certain substitutions and purifying selection that constrains substitutions to a small number of functionally equivalent amino acids.
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Affiliation(s)
- Antonis Rokas
- Department of Biological Sciences, Vanderbilt University, USA
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18
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Antezana MA, Jordan IK. Highly conserved regimes of neighbor-base-dependent mutation generated the background primary-structural heterogeneities along vertebrate chromosomes. PLoS One 2008; 3:e2145. [PMID: 18478116 PMCID: PMC2366069 DOI: 10.1371/journal.pone.0002145] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2007] [Accepted: 03/17/2008] [Indexed: 01/01/2023] Open
Abstract
The content of guanine+cytosine varies markedly along the chromosomes of homeotherms and great effort has been devoted to studying this heterogeneity and its biological implications. Already before the DNA-sequencing era, however, it was established that the dinucleotides in the DNA of mammals in particular, and of most organisms in general, show striking over- and under-representations that cannot be explained by the base composition. Here we show that in the coding regions of vertebrates both GC content and codon occurrences are strongly correlated with such "motif preferences" even though we quantify the latter using an index that is not affected by the base composition, codon usage, and protein-sequence encoding. These correlations are likely to be the result of the long-term shaping of the primary structure of genic and non-genic DNA by a regime of mutation of which central features have been maintained by natural selection. We find indeed that these preferences are conserved in vertebrates even more rigidly than codon occurrences and we show that the occurrence-preference correlations are stronger in intronic and non-genic DNA, with the R(2)s reaching 99% when GC content is approximately 0.5. The mutation regime appears to be characterized by rates that depend markedly on the bases present at the site preceding and at that following each mutating site, because when we estimate such rates of neighbor-base-dependent mutation (NBDM) from substitutions retrieved from alignments of coding, intronic, and non-genic mammalian DNA sorted and grouped by GC content, they suffice to simulate DNA sequences in which motif occurrences and preferences as well as the correlations of motif preferences with GC content and with motif occurrences, are very similar to the mammalian ones. The best fit, however, is obtained with NBDM regimes lacking strand effects, which indicates that over the long term NBDM switches strands in the germline as one would expect for effects due to loosely contained background transcription. Finally, we show that human coding regions are less mutable under the estimated NBDM regimes than under matched context-independent mutation and that this entails marked differences between the spectra of amino-acid mutations that either mutation regime should generate. In the Discussion we examine the mechanisms likely to underlie NBDM heterogeneity along chromosomes and propose that it reflects how the diversity and activity of lesion-bypass polymerases (LBPs) track the landscapes of scheduled and non-scheduled genome repair, replication, and transcription during the cell cycle. We conclude that the primary structure of vertebrate genic DNA at and below the trinucleotide level has been governed over the long term by highly conserved regimes of NBDM which should be under direct natural selection because they alter drastically missense-mutation rates and hence the somatic and the germline mutational loads. Therefore, the non-coding DNA of vertebrates may have been shaped by NBDM only epiphenomenally, with non-genic DNA being affected mainly when found in the proximity of genes.
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Affiliation(s)
- Marcos A Antezana
- Department of Ecology and Evolution, University of Chicago, Chicago, Illinois, United States of America.
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19
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Scannell DR, Wolfe KH. A burst of protein sequence evolution and a prolonged period of asymmetric evolution follow gene duplication in yeast. Genes Dev 2008; 18:137-47. [PMID: 18025270 PMCID: PMC2134778 DOI: 10.1101/gr.6341207] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2007] [Accepted: 09/23/2007] [Indexed: 11/24/2022]
Abstract
It is widely accepted that newly arisen duplicate gene pairs experience an altered selective regime that is often manifested as an increase in the rate of protein sequence evolution. Many details about the nature of the rate acceleration remain unknown, however, including its typical magnitude and duration, and whether it applies to both gene copies or just one. We provide initial answers to these questions by comparing the rate of protein sequence evolution among eight yeast species, between a large set of duplicate gene pairs that were created by a whole-genome duplication (WGD) and a set of genes that were returned to single-copy after this event. Importantly, we use a new method that takes into account the tendency for slowly evolving genes to be retained preferentially in duplicate. We show that, on average, proteins encoded by duplicate gene pairs evolved at least three times faster immediately after the WGD than single-copy genes to which they behave identically in non-WGD lineages. Although the high rate in duplicated genes subsequently declined rapidly, it has not yet returned to the typical rate for single-copy genes. In addition, we show that although duplicate gene pairs often have highly asymmetric rates of evolution, even the slower members of pairs show evidence of a burst of protein sequence evolution immediately after duplication. We discuss the contribution of neofunctionalization to duplicate gene preservation and propose that a form of subfunctionalization mediated by coding region activity-reducing mutations is likely to have played an important role.
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Affiliation(s)
- Devin R Scannell
- Smurfit Institute of Genetics, Trinity College Dublin, Dublin 2, Ireland.
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20
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Hanada K, Shiu SH, Li WH. The Nonsynonymous/Synonymous Substitution Rate Ratio versus the Radical/Conservative Replacement Rate Ratio in the Evolution of Mammalian Genes. Mol Biol Evol 2007; 24:2235-41. [PMID: 17652332 DOI: 10.1093/molbev/msm152] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
There are 2 ways to infer selection pressures in the evolution of protein-coding genes, the nonsynonymous and synonymous substitution rate ratio (K(A)/K(S)) and the radical and conservative amino acid replacement rate ratio (K(R)/K(C)). Because the K(R)/K(C) ratio depends on the definition of radical and conservative changes in the classification of amino acids, we develop an amino acid classification that maximizes the correlation between K(A)/K(S) and K(R)/K(C). An analysis of 3,375 orthologous gene groups among 5 mammalian species shows that our classification gives a significantly higher correlation coefficient between the 2 ratios than those of existing classifications. However, there are many orthologous gene groups with a low K(A)/K(S) but a high K(R)/K(C) ratio. Examining the functions of these genes, we found an overrepresentation of functional categories related to development. To determine if the overrepresentation is stage specific, we examined the expression patterns of these genes at different developmental stages of the mouse. Interestingly, these genes are highly expressed in the early middle stage of development (blastocyst to amnion). It is commonly thought that developmental genes tend to be conservative in evolution, but some molecular changes in developmental stages should have contributed to morphological divergence in adult mammals. Therefore, we propose that the relaxed pressures indicated by the K(R)/K(C) ratio but not by K(A)/K(S) in the early middle stage of development may be important for the morphological divergence of mammals at the adult stage, whereas purifying selection detected by K(A)/K(S) occurs in the early middle developmental stage.
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Affiliation(s)
- Kousuke Hanada
- Department of Ecology and Evolution, University of Chicago, USA
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21
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Nickle DC, Heath L, Jensen MA, Gilbert PB, Mullins JI, Kosakovsky Pond SL. HIV-specific probabilistic models of protein evolution. PLoS One 2007; 2:e503. [PMID: 17551583 PMCID: PMC1876811 DOI: 10.1371/journal.pone.0000503] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2007] [Accepted: 05/08/2007] [Indexed: 11/19/2022] Open
Abstract
Comparative sequence analyses, including such fundamental bioinformatics techniques as similarity searching, sequence alignment and phylogenetic inference, have become a mainstay for researchers studying type 1 Human Immunodeficiency Virus (HIV-1) genome structure and evolution. Implicit in comparative analyses is an underlying model of evolution, and the chosen model can significantly affect the results. In general, evolutionary models describe the probabilities of replacing one amino acid character with another over a period of time. Most widely used evolutionary models for protein sequences have been derived from curated alignments of hundreds of proteins, usually based on mammalian genomes. It is unclear to what extent these empirical models are generalizable to a very different organism, such as HIV-1–the most extensively sequenced organism in existence. We developed a maximum likelihood model fitting procedure to a collection of HIV-1 alignments sampled from different viral genes, and inferred two empirical substitution models, suitable for describing between-and within-host evolution. Our procedure pools the information from multiple sequence alignments, and provided software implementation can be run efficiently in parallel on a computer cluster. We describe how the inferred substitution models can be used to generate scoring matrices suitable for alignment and similarity searches. Our models had a consistently superior fit relative to the best existing models and to parameter-rich data-driven models when benchmarked on independent HIV-1 alignments, demonstrating evolutionary biases in amino-acid substitution that are unique to HIV, and that are not captured by the existing models. The scoring matrices derived from the models showed a marked difference from common amino-acid scoring matrices. The use of an appropriate evolutionary model recovered a known viral transmission history, whereas a poorly chosen model introduced phylogenetic error. We argue that our model derivation procedure is immediately applicable to other organisms with extensive sequence data available, such as Hepatitis C and Influenza A viruses.
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Affiliation(s)
- David C. Nickle
- Department of Microbiology, University of Washington School of Medicine, Seattle, Washington, United States of America
| | - Laura Heath
- Department of Microbiology, University of Washington School of Medicine, Seattle, Washington, United States of America
| | - Mark A. Jensen
- Department of Microbiology, University of Washington School of Medicine, Seattle, Washington, United States of America
| | - Peter B. Gilbert
- Department of Biostatistics, University of Washington and Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America
| | - James I. Mullins
- Department of Microbiology, University of Washington School of Medicine, Seattle, Washington, United States of America
| | - Sergei L. Kosakovsky Pond
- Department of Pathology, University of California, San Diego, La Jolla, California, United States of America
- * To whom correspondence should be addressed. E-mail:
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22
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Starkweather R, Barnes CS, Wyckoff GJ, Keightley JA. Virtual polymorphism: finding divergent peptide matches in mass spectrometry data. Anal Chem 2007; 79:5030-9. [PMID: 17521167 DOI: 10.1021/ac0703496] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The prevailing method of analyzing tandem-MS data for protein identification involves the comparison of peptide molecular weight and fragmentation data to theoretically predicted values, based on known protein sequences in databases. This is generally effective since proteins from most species under study are in the database or have sufficient homology to allow significant matching. We have encountered difficulties identifying proteins from fungal species Alternaria alternata due to significant interspecies protein sequence differences (divergence) and its absence from the database. This common household mold causes asthma and allergy problems, but the genome has not been sequenced. De novo sequencing and error-tolerant methods can facilitate protein identifications in divergent, unsequenced species. But these standard methods can be laborious and only allow single amino acid substitution, respectively. We have developed an alternative approach focusing on database engineering, predicting biologically rational polymorphism using statistically weighted amino acid substitution information held in BLOSUM62. Like other second pass methods, it is based on the initially identified protein. However, this approach allows more control over sequences to be considered, including multiple changes per peptide. The results show considerable improvement for routine protein identification and the potential for rescuing otherwise unconvincing identifications in unusually divergent species.
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Affiliation(s)
- Rebekah Starkweather
- Division of Molecular Biology and Biochemistry, University of Missouri-Kansas City, 5007 Rockhill Road, Kansas City, Missouri 64110, USA
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Gojobori J, Tang H, Akey JM, Wu CI. Adaptive evolution in humans revealed by the negative correlation between the polymorphism and fixation phases of evolution. Proc Natl Acad Sci U S A 2007; 104:3907-12. [PMID: 17360451 PMCID: PMC1820682 DOI: 10.1073/pnas.0605565104] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The selective forces acting on amino acid substitutions may be different in the two phases of molecular evolution: polymorphism and fixation. Negative selection and genetic drift may dominate the first phase, whereas positive selection may become much more significant in the second phase. However, the conventional dichotomy of synonymous vs. nonsynonymous changes does not offer the resolution needed to study the dynamics of these two phases. Following previously published methods, we separated amino acid changes into 75 elementary types (1-bp substitution between their respective codons). The likelihood of each type of amino acid change becoming polymorphic (PI, which stands for "polymorphic index"), relative to synonymous changes, can then be calculated. Similarly, the likelihood of fixation (FI, for "fixation index"), conditional on common polymorphisms, is also calculated. Using Perlegen and HapMap data on human polymorphisms and the chimpanzee sequences as the outgroup, we compared the evolutionary dynamics of the 75 elementary changes in the two phases. We found a strong "L-shaped" negative correlation (P < 0.001) between FI and PI. Only those changes with low PIs show FI > 1, which is often a signature of adaptive evolution. These patterns suggest that negative and positive selection operate more effectively on the same set of amino acid changes and that approximately 10-13% of amino acid substitutions between humans and chimpanzee may be adaptive.
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Affiliation(s)
- Jun Gojobori
- *Department of Biological Sciences, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
- Department of Ecology and Evolution, University of Chicago, 1101 East 57th Street, Chicago, IL 60637; and
| | - Hua Tang
- Department of Ecology and Evolution, University of Chicago, 1101 East 57th Street, Chicago, IL 60637; and
| | - Joshua M. Akey
- Department of Genome Sciences, University of Washington, 1705 NE Pacific Street, #K-357, HSB J-279, Seattle, WA 98195
| | - Chung-I Wu
- Department of Ecology and Evolution, University of Chicago, 1101 East 57th Street, Chicago, IL 60637; and
- To whom correspondence should be addressed. E-mail:
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Shapiro JA, Huang W, Zhang C, Hubisz MJ, Lu J, Turissini DA, Fang S, Wang HY, Hudson RR, Nielsen R, Chen Z, Wu CI. Adaptive genic evolution in the Drosophila genomes. Proc Natl Acad Sci U S A 2007; 104:2271-6. [PMID: 17284599 PMCID: PMC1892965 DOI: 10.1073/pnas.0610385104] [Citation(s) in RCA: 196] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2006] [Indexed: 11/18/2022] Open
Abstract
Determining the extent of adaptive evolution at the genomic level is central to our understanding of molecular evolution. A suitable observation for this purpose would consist of polymorphic data on a large and unbiased collection of genes from two closely related species, each having a large and stable population. In this study, we sequenced 419 genes from 24 lines of Drosophila melanogaster and its close relatives. Together with data from Drosophila simulans, these data reveal the following. (i) Approximately 10% of the loci in regions of normal recombination are much less polymorphic at silent sites than expected, hinting at the action of selective sweeps. (ii) The level of polymorphism is negatively correlated with the rate of nonsynonymous divergence across loci. Thus, even under strict neutrality, the ratio of amino acid to silent nucleotide changes (A:S) between Drosophila species is expected to be 25-40% higher than the A:S ratio for polymorphism when data are pooled across the genome. (iii) The observed A/S ratio between species among the 419 loci is 28.9% higher than the (adjusted) neutral expectation. We estimate that nearly 30% of the amino acid substitutions between D. melanogaster and its close relatives were adaptive. (iv) This signature of adaptive evolution is observable only in regions of normal recombination. Hence, the low level of polymorphism observed in regions of reduced recombination may not be driven primarily by positive selection. Finally, we discuss the theories and data pertaining to the interpretation of adaptive evolution in genomic studies.
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Affiliation(s)
| | - Wei Huang
- Department of Genetics, Chinese National Human Genome Center at Shanghai, Shanghai 201203, China
| | - Chenhui Zhang
- Department of Genetics, Chinese National Human Genome Center at Shanghai, Shanghai 201203, China
| | | | - Jian Lu
- Departments of *Ecology and Evolution and
| | | | - Shu Fang
- Departments of *Ecology and Evolution and
| | | | | | - Rasmus Nielsen
- Institute of Biology, University of Copenhagen, DK-1100 Copenhagen, Denmark
| | - Zhu Chen
- Department of Genetics, Chinese National Human Genome Center at Shanghai, Shanghai 201203, China
- State Key Laboratory of Medical Genomics and Shanghai Institute of Hematology, Rui-Jin Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, 201203, China; and
| | - Chung-I Wu
- Departments of *Ecology and Evolution and
- **International Center for Evolutionary and Genomic Studies, Sun Yat-Sen University, Guangzhou 510275, China
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Jagadeeshan S, Singh RS. Rapid Evolution of Outer Egg Membrane Proteins in the Drosophila melanogaster Subgroup: A Case of Ecologically Driven Evolution of Female Reproductive Traits. Mol Biol Evol 2007; 24:929-38. [PMID: 17244601 DOI: 10.1093/molbev/msm009] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Although sexual selection has been predominantly used to explain the rapid evolution of sexual traits, eggs of oviparous organisms directly face both the challenges of sexual selection as well as natural selection (environmental challenges, survival in niches, etc.). Being the outermost membrane in most insect eggs, the chorion layer is the interface between the embryo and the environment, thereby serving to protect the egg. Adaptive ecological radiations such as divergence in ovipositional substrate usage and host-plant specializations can therefore influence the evolution of eggshell proteins. We can hypothesize that proteins localized on the outer eggshell may be affected to a greater degree by ecological challenges compared with inner eggshell proteins, and therefore, proteins localized in the outer eggshell (chorion membrane) may evolve differently (faster) than proteins localized in the inner egg membrane (vitelline membrane). We compared the evolutionary divergence of vitelline with chorion membrane proteins in species of the melanogaster subgroup and found that chorion proteins as a group are indeed evolving faster than vitelline membrane proteins. At least one vitelline membrane protein (Vm32E), specifically localized on the outer eggshell, is also evolving faster than other vitelline membrane proteins suggesting that all proteins localized on the outer eggshell may be evolving rapidly. We also found evidence that specific codons in chorion proteins cp15 and cp16 are evolving under positive selection. Polymorphism surveys of cp16 revealed inflated levels of divergence relative to polymorphism in specific regions of the gene, indicating that these regions are under strong selection. At the morphological level, we found notable difference in eggshell surface morphologies between specialist (Drosophila sechellia and Drosophila erecta) and generalist species of Drosophila. We do not know if any of the chorion proteins actually interact with spermatozoids, therefore leaving the possibility of rapid evolution through gametic interaction wide open. At this point, however, our results support previous suggestions that divergences in ecology, particularly, ovipositional substrate divergences may be a strong force driving the evolution of eggshell proteins.
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Evolutionary anatomies of positions and types of disease-associated and neutral amino acid mutations in the human genome. BMC Genomics 2006; 7:306. [PMID: 17144929 PMCID: PMC1702542 DOI: 10.1186/1471-2164-7-306] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2006] [Accepted: 12/05/2006] [Indexed: 02/02/2023] Open
Abstract
Background Amino acid mutations in a large number of human proteins are known to be associated with heritable genetic disease. These disease-associated mutations (DAMs) are known to occur predominantly in positions essential to the structure and function of the proteins. Here, we examine how the relative perpetuation and conservation of amino acid positions modulate the genome-wide patterns of 8,627 human disease-associated mutations (DAMs) reported in 541 genes. We compare these patterns with 5,308 non-synonymous Single Nucleotide Polymorphisms (nSNPs) in 2,592 genes from primary SNP resources. Results The abundance of DAMs shows a negative relationship with the evolutionary rate of the amino acid positions harboring them. An opposite trend describes the distribution of nSNPs. DAMs are also preferentially found in the amino acid positions that are retained (or present) in multiple vertebrate species, whereas the nSNPs are over-abundant in the positions that have been lost (or absent) in the non-human vertebrates. These observations are consistent with the effect of purifying selection on natural variation, which also explains the existence of lower minor nSNP allele frequencies at highly-conserved amino acid positions. The biochemical severity of the inter-specific amino acid changes is also modulated by natural selection, with the fast-evolving positions containing more radical amino acid differences among species. Similarly, DAMs associated with early-onset diseases are more radical than those associated with the late-onset diseases. A small fraction of DAMs (10%) overlap with the amino acid differences between species within the same position, but are biochemically the most conservative group of amino acid differences in our datasets. Overlapping DAMs are found disproportionately in fast-evolving amino acid positions, which, along with the conservative nature of the amino acid changes, may have allowed some of them to escape natural selection until compensatory changes occur. Conclusion The consistency and predictability of genome-wide patterns of disease- associated and neutral amino acid variants reported here underscores the importance of the consideration of evolutionary rates of amino acid positions in clinical and population genetic analyses aimed at understanding the nature and fate of disease-associated and neutral population variation. Establishing such general patterns is an early step in efforts to diagnose the pathogenic potentials of novel amino acid mutations.
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Plotkin JB, Dushoff J, Desai MM, Fraser HB. Codon usage and selection on proteins. J Mol Evol 2006; 63:635-53. [PMID: 17043750 DOI: 10.1007/s00239-005-0233-x] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2005] [Accepted: 06/12/2006] [Indexed: 10/24/2022]
Abstract
Selection pressures on proteins are usually measured by comparing homologous nucleotide sequences (Zuckerkandl and Pauling 1965). Recently we introduced a novel method, termed volatility, to estimate selection pressures on proteins on the basis of their synonymous codon usage (Plotkin and Dushoff 2003; Plotkin et al. 2004). Here we provide a theoretical foundation for this approach. Under the Fisher-Wright model, we derive the expected frequencies of synonymous codons as a function of the strength of selection on amino acids, the mutation rate, and the effective population size. We analyze the conditions under which we can expect to draw inferences from biased codon usage, and we estimate the time scales required to establish and maintain such a signal. We find that synonymous codon usage can reliably distinguish between negative selection and neutrality only for organisms, such as some microbes, that experience large effective population sizes or periods of elevated mutation rates. The power of volatility to detect positive selection is also modest--requiring approximately 100 selected sites--but it depends less strongly on population size. We show that phenomena such as transient hyper-mutators can improve the power of volatility to detect selection, even when the neutral site heterozygosity is low. We also discuss several confounding factors, neglected by the Fisher-Wright model, that may limit the applicability of volatility in practice.
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Affiliation(s)
- Joshua B Plotkin
- Department of Biology, University of Pennsylvania, Philadelphia, PA 19104, USA.
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28
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Abstract
Evolutionary trends responsible for systematic differences in genome and proteome composition have been attributed to GC:AT mutation bias in the context of neutral evolution or to selection acting on genome composition. A possibility that has been ignored, presumably because it is part of neither the Modern Synthesis nor the Neutral Theory, is that mutation may impose a directional bias on adaptation. This possibility is explored here with simulations of the effect of a GC:AT bias on amino acid composition during adaptive walks on an abstract protein fitness landscape called an "NK" model. The results indicate that adaptation does not preclude mutation-biased evolution. In the complete absence of neutral evolution, a modest GC:AT bias of realistic magnitude can displace the trajectory of adaptation in a mutationally favored direction, to such a degree that amino acid composition is biased substantially and persistently. Thus, mutational explanations for evolved patterns need not presuppose neutral evolution.
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Affiliation(s)
- Arlin Stoltzfus
- Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute, Gaithersburg, Maryland, USA.
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Zhang J. Parallel adaptive origins of digestive RNases in Asian and African leaf monkeys. Nat Genet 2006; 38:819-23. [PMID: 16767103 DOI: 10.1038/ng1812] [Citation(s) in RCA: 158] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2005] [Accepted: 04/27/2006] [Indexed: 11/08/2022]
Abstract
Similar morphological or physiological changes occurring in multiple evolutionary lineages are not uncommon. Such parallel changes are believed to be adaptive, because a complex character is unlikely to originate more than once by chance. However, the occurrence of adaptive parallel amino acid substitutions is debated. Here I propose four requirements for establishing adaptive parallel evolution at the protein sequence level and use these criteria to demonstrate such a case. I report that the gene encoding pancreatic ribonuclease was duplicated independently in Asian and African leaf-eating monkeys. Statistical analyses of DNA sequences, functional assays of reconstructed ancestral proteins and site-directed mutagenesis show that the new genes acquired enhanced digestive efficiencies through parallel amino acid replacements driven by darwinian selection. They also lost a non-digestive function independently, under a relaxed selective constraint. These results demonstrate that despite the overall stochasticity, even molecular evolution has a certain degree of repeatability and predictability under the pressures of natural selection.
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Affiliation(s)
- Jianzhi Zhang
- Department of Ecology and Evolutionary Biology, University of Michigan, 1075 Natural Science Building, 830 North University Avenue, Ann Arbor, Michigan 48109, USA.
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Lu J, Tang T, Tang H, Huang J, Shi S, Wu CI. The accumulation of deleterious mutations in rice genomes: a hypothesis on the cost of domestication. Trends Genet 2006; 22:126-31. [PMID: 16443304 DOI: 10.1016/j.tig.2006.01.004] [Citation(s) in RCA: 137] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2005] [Revised: 12/07/2005] [Accepted: 01/13/2006] [Indexed: 11/20/2022]
Abstract
The extent of molecular differentiation between domesticated animals or plants and their wild relatives is postulated to be small. The availability of the complete genome sequences of two subspecies of the Asian rice, Oryza sativa (indica and japonica) and their wild relatives have provided an unprecedented opportunity to study divergence following domestication. We observed significantly more amino acid substitutions during rice domestication than can be expected from a comparison among wild species. This excess is disproportionately larger for the more radical kinds of amino acid changes (e.g. Cys<-->Tyr). We estimate that approximately a quarter of the amino acid differences between rice cultivars are deleterious, not accountable by the relaxation of selective constraints. This excess is negatively correlated with the rate of recombination, suggesting that 'hitchhiking' has occurred. We hypothesize that during domestication artificial selection increased the frequency of many deleterious mutations.
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Affiliation(s)
- Jian Lu
- Department of Ecology and Evolution, University of Chicago, 1101 East 57th Street, Chicago, IL 60637, USA
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Tang H, Wu CI. A new method for estimating nonsynonymous substitutions and its applications to detecting positive selection. Mol Biol Evol 2005; 23:372-9. [PMID: 16237204 DOI: 10.1093/molbev/msj043] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The standard methods for computing the number of nonsynonymous substitutions (Ka) lump all amino acid changes into one single class, even though their rates of substitution vary by at least 10-fold (Tang et al., 2004). Classifying these changes by their physicochemical properties has not been suitably effective in isolating the fastest evolving classes of changes. We now propose to use the Universal index U of Tang et al. (2004) to classify the 75 elementary amino acid changes (codons differing by 1 bp) by their evolutionary exchangeability. Let Ki denote the Ka value of each class (i = 1, ..., 75 from the most to the least exchangeable). The cumulative Ki for the top 10 classes, denoted Kh (for high-exchangeability types), has two important properties: (1) Kh usually accounts for 25%-30% of total amino acid changes and (2) when the observed number of amino acid substitutions is large, Kh is predictably twice the value of Ka. This shall be referred to as the twofold approximation. The new method for estimating Kh is applied to the comparisons between human and macaque and between mouse and rat. The twofold approximation holds well in these data sets, and the signature of positive selection can be more easily discerned using the Kh statistic than using Ka. Many genes with Ka/Ks > 0.5 can now be shown to have Kh/Ks > 1 and to have evolved adaptively, at least for the high-exchangeability group of amino acid changes.
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Affiliation(s)
- Hua Tang
- Department of Ecology and Evolution, University of Chicago, USA
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Yampolsky LY, Kondrashov FA, Kondrashov AS. Distribution of the strength of selection against amino acid replacements in human proteins. Hum Mol Genet 2005; 14:3191-201. [PMID: 16174645 DOI: 10.1093/hmg/ddi350] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The impact of an amino acid replacement on the organism's fitness can vary from lethal to selectively neutral and even, in rare cases, beneficial. Substantial data are available on either pathogenic or acceptable replacements. However, the whole distribution of coefficients of selection against individual replacements is not known for any organism. To ascertain this distribution for human proteins, we combined data on pathogenic missense mutations, on human non-synonymous SNPs and on human-chimpanzee divergence of orthologous proteins. Fractions of amino acid replacements which reduce fitness by >10(-2), 10(-2)-10(-4), 10(-4)-10(-5) and <10(-5) are 25, 49, 14 and 12%, respectively. On average, the strength of selection against a replacement is substantially higher when chemically dissimilar amino acids are involved, and the Grantham's index of a replacement explains 35% of variance in the average logarithm of selection coefficients associated with different replacements. Still, the impact of a replacement depends on its context within the protein more than on its own nature. Reciprocal replacements are often associated with rather different selection coefficients, in particular, replacements of non-polar amino acids with polar ones are typically much more deleterious than replacements in the opposite direction. However, differences between evolutionary fluxes of reciprocal replacements are only weakly correlated with the differences between the corresponding selection coefficients.
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Affiliation(s)
- Lev Y Yampolsky
- Department of Biological Sciences, East Tennessee State University, Johnson City, TN 37614-1710, USA
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