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  • 1
    Publication Date: 2013-07-23
    Description: The dynamics of adaptation determine which mutations fix in a population, and hence how reproducible evolution will be. This is central to understanding the spectra of mutations recovered in the evolution of antibiotic resistance, the response of pathogens to immune selection, and the dynamics of cancer progression. In laboratory evolution experiments, demonstrably beneficial mutations are found repeatedly, but are often accompanied by other mutations with no obvious benefit. Here we use whole-genome whole-population sequencing to examine the dynamics of genome sequence evolution at high temporal resolution in 40 replicate Saccharomyces cerevisiae populations growing in rich medium for 1,000 generations. We find pervasive genetic hitchhiking: multiple mutations arise and move synchronously through the population as mutational 'cohorts'. Multiple clonal cohorts are often present simultaneously, competing with each other in the same population. Our results show that patterns of sequence evolution are driven by a balance between these chance effects of hitchhiking and interference, which increase stochastic variation in evolutionary outcomes, and the deterministic action of selection on individual mutations, which favours parallel evolutionary solutions in replicate populations.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3758440/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3758440/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Lang, Gregory I -- Rice, Daniel P -- Hickman, Mark J -- Sodergren, Erica -- Weinstock, George M -- Botstein, David -- Desai, Michael M -- GM046406/GM/NIGMS NIH HHS/ -- GM071508/GM/NIGMS NIH HHS/ -- P50 GM071508/GM/NIGMS NIH HHS/ -- R01 GM046406/GM/NIGMS NIH HHS/ -- R37 GM046406/GM/NIGMS NIH HHS/ -- England -- Nature. 2013 Aug 29;500(7464):571-4. doi: 10.1038/nature12344. Epub 2013 Jul 21.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Lewis-Sigler Institute for Integrative Genomics and Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA. glang@lehigh.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/23873039" target="_blank"〉PubMed〈/a〉
    Keywords: Adaptation, Physiological/genetics ; Cell Nucleus/genetics ; Clone Cells/*cytology/metabolism ; *Evolution, Molecular ; Genes, Fungal/genetics ; Mutation/genetics ; Saccharomyces cerevisiae/classification/cytology/*genetics/*growth & development ; Stochastic Processes ; Time Factors
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 2
    Publication Date: 2014-06-28
    Description: Epistatic interactions between mutations can make evolutionary trajectories contingent on the chance occurrence of initial mutations. We used experimental evolution in Saccharomyces cerevisiae to quantify this contingency, finding differences in adaptability among 64 closely related genotypes. Despite these differences, sequencing of 104 evolved clones showed that initial genotype did not constrain future mutational trajectories. Instead, reconstructed combinations of mutations revealed a pattern of diminishing-returns epistasis: Beneficial mutations have consistently smaller effects in fitter backgrounds. Taken together, these results show that beneficial mutations affecting a variety of biological processes are globally coupled; they interact strongly, but only through their combined effect on fitness. As a consequence, fitness evolution follows a predictable trajectory even though sequence-level adaptation is stochastic.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4314286/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4314286/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Kryazhimskiy, Sergey -- Rice, Daniel P -- Jerison, Elizabeth R -- Desai, Michael M -- GM104239/GM/NIGMS NIH HHS/ -- R01 GM104239/GM/NIGMS NIH HHS/ -- New York, N.Y. -- Science. 2014 Jun 27;344(6191):1519-22. doi: 10.1126/science.1250939.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA. FAS Center for Systems Biology, Harvard University, Cambridge, MA 02138, USA. skryazhi@oeb.harvard.edu mdesai@oeb.harvard.edu. ; Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA. FAS Center for Systems Biology, Harvard University, Cambridge, MA 02138, USA. ; Department of Physics, Harvard University, Cambridge, MA 02138, USA. FAS Center for Systems Biology, Harvard University, Cambridge, MA 02138, USA. ; Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA. Department of Physics, Harvard University, Cambridge, MA 02138, USA. FAS Center for Systems Biology, Harvard University, Cambridge, MA 02138, USA. skryazhi@oeb.harvard.edu mdesai@oeb.harvard.edu.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24970088" target="_blank"〉PubMed〈/a〉
    Keywords: *Adaptation, Physiological ; Base Sequence ; Directed Molecular Evolution ; *Epistasis, Genetic ; *Evolution, Molecular ; Genes, Fungal ; *Genetic Fitness ; Genome, Fungal ; Genotype ; Models, Genetic ; Molecular Sequence Annotation ; Mutation ; Saccharomyces cerevisiae/*genetics/*physiology ; Sequence Analysis, DNA ; Stochastic Processes
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 3
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    American Association for the Advancement of Science (AAAS)
    Publication Date: 2015-05-30
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Desai, Michael M -- Walczak, Aleksandra M -- New York, N.Y. -- Science. 2015 May 29;348(6238):977-8. doi: 10.1126/science.aab3957.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Departments of Organismic and Evolutionary Biology and of Physics, Harvard University, Cambridge, MA 02138, USA. ; CNRS, Laboratoire de Physique Theorique, Ecole Normale Superieure, 75 231 Paris Cedex 05, France. awalczak@lpt.ens.fr.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26023126" target="_blank"〉PubMed〈/a〉
    Keywords: *Evolution, Molecular ; *Polymorphism, Single Nucleotide ; *Recombination, Genetic ; Synechococcus/*genetics
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 4
    Publication Date: 2016-02-26
    Description: Sex and recombination are pervasive throughout nature despite their substantial costs. Understanding the evolutionary forces that maintain these phenomena is a central challenge in biology. One longstanding hypothesis argues that sex is beneficial because recombination speeds adaptation. Theory has proposed several distinct population genetic mechanisms that could underlie this advantage. For example, sex can promote the fixation of beneficial mutations either by alleviating interference competition (the Fisher-Muller effect) or by separating them from deleterious load (the ruby in the rubbish effect). Previous experiments confirm that sex can increase the rate of adaptation, but these studies did not observe the evolutionary dynamics that drive this effect at the genomic level. Here we present the first, to our knowledge, comparison between the sequence-level dynamics of adaptation in experimental sexual and asexual Saccharomyces cerevisiae populations, which allows us to identify the specific mechanisms by which sex speeds adaptation. We find that sex alters the molecular signatures of evolution by changing the spectrum of mutations that fix, and confirm theoretical predictions that it does so by alleviating clonal interference. We also show that substantially deleterious mutations hitchhike to fixation in adapting asexual populations. In contrast, recombination prevents such mutations from fixing. Our results demonstrate that sex both speeds adaptation and alters its molecular signature by allowing natural selection to more efficiently sort beneficial from deleterious mutations.〈br /〉〈br /〉〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4855304/" target="_blank"〉〈img src="https://static.pubmed.gov/portal/portal3rc.fcgi/4089621/img/3977009" border="0"〉〈/a〉   〈a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4855304/" target="_blank"〉This paper as free author manuscript - peer-reviewed and accepted for publication〈/a〉〈br /〉〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉McDonald, Michael J -- Rice, Daniel P -- Desai, Michael M -- GM104239/GM/NIGMS NIH HHS/ -- R01 GM104239/GM/NIGMS NIH HHS/ -- England -- Nature. 2016 Mar 10;531(7593):233-6. doi: 10.1038/nature17143. Epub 2016 Feb 24.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA. ; FAS Center for Systems Biology, Harvard University, Cambridge, Massachusetts 02138, USA. ; Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26909573" target="_blank"〉PubMed〈/a〉
    Keywords: Adaptation, Physiological/*genetics ; Clone Cells/cytology/metabolism ; *Evolution, Molecular ; Genetic Fitness/genetics ; Genetics, Population ; Models, Genetic ; Mutation/*genetics ; Recombination, Genetic/genetics ; Reproduction, Asexual/genetics/*physiology ; Saccharomyces cerevisiae/cytology/*genetics/*physiology ; Selection, Genetic/*genetics ; *Sex ; Time Factors
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 5
    Publication Date: 2012-02-27
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 6
    Publication Date: 2014-02-12
    Description: The origins of evolutionary novelty are notoriously difficult to predict in advance or even to pinpoint in retrospect. Qualitatively new traits can arise due to complex mutational events, such as regulatory changes (1), or exaptation of genes coding for existing functions (2). This often involves multiple mutations that are all...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 7
    Publication Date: 2012-03-28
    Description: When large asexual populations adapt, competition between simultaneously segregating mutations slows the rate of adaptation and restricts the set of mutations that eventually fix. This phenomenon of interference arises from competition between mutations of different strengths as well as competition between mutations that arise on different fitness backgrounds. Previous work has explored each of these effects in isolation, but the way they combine to influence the dynamics of adaptation remains largely unknown. Here, we describe a theoretical model to treat both aspects of interference in large populations. We calculate the rate of adaptation and the distribution of fixed mutational effects accumulated by the population. We focus particular attention on the case when the effects of beneficial mutations are exponentially distributed, as well as on a more general class of exponential-like distributions. In both cases, we show that the rate of adaptation and the influence of genetic background on the fixation of new mutants is equivalent to an effective model with a single selection coefficient and rescaled mutation rate, and we explicitly calculate these effective parameters. We find that the effective selection coefficient exactly coincides with the most common fixed mutational effect. This equivalence leads to an intuitive picture of the relative importance of different types of interference effects, which can shift dramatically as a function of the population size, mutation rate, and the underlying distribution of fitness effects.
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 8
    Publication Date: 2012-10-17
    Description: Purifying selection can substantially alter patterns of molecular evolution. Its main effect is to reduce overall levels of genetic variation, leading to a reduced effective population size. However, it also distorts genealogies relative to neutral expectations. A structured coalescent method has been used to describe this effect, and forms the basis for numerical methods and simulations. In this study, we extend this approach by making the additional approximation that lineages may be treated independently, which is valid only in the strong selection regime. We show that in this regime, the distortions due to purifying selection can be described by a time-dependent effective population size and mutation rate, confirming earlier intuition. We calculate simple analytical expressions for these functions, N e ( t ) and U e ( t ). These results allow us to describe the structure of genealogies in a population under strong purifying selection as equivalent to a purely neutral population with varying population size and mutation rate, thereby enabling the use of neutral methods of inference and estimation for populations in the strong selection regime.
    Print ISSN: 0737-4038
    Electronic ISSN: 1537-1719
    Topics: Biology
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  • 9
    Publication Date: 2015-09-09
    Description: Natural environments are never truly constant, but the evolutionary implications of temporally varying selection pressures remain poorly understood. Here we investigate how the fate of a new mutation in a fluctuating environment depends on the dynamics of environmental variation and on the selective pressures in each condition. We find that...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 10
    Publication Date: 2015-09-09
    Description: Identifying the mechanisms that create and maintain biodiversity is a central challenge in biology. Stable diversification of microbial populations often requires the evolution of differences in resource utilization. Alternatively, coexistence can be maintained by specialization to exploit spatial heterogeneity in the environment. Here, we report spontaneous diversification maintained by a...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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