1
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Chase MA, Vilcot M, Mugal CF. The role of recombination dynamics in shaping signatures of direct and indirect selection across the Ficedula flycatcher genome †. Proc Biol Sci 2024; 291:20232382. [PMID: 38228173 DOI: 10.1098/rspb.2023.2382] [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: 10/20/2022] [Accepted: 12/14/2023] [Indexed: 01/18/2024] Open
Abstract
Recombination is a central evolutionary process that reshuffles combinations of alleles along chromosomes, and consequently is expected to influence the efficacy of direct selection via Hill-Robertson interference. Additionally, the indirect effects of selection on neutral genetic diversity are expected to show a negative relationship with recombination rate, as background selection and genetic hitchhiking are stronger when recombination rate is low. However, owing to the limited availability of recombination rate estimates across divergent species, the impact of evolutionary changes in recombination rate on genomic signatures of selection remains largely unexplored. To address this question, we estimate recombination rate in two Ficedula flycatcher species, the taiga flycatcher (Ficedula albicilla) and collared flycatcher (Ficedula albicollis). We show that recombination rate is strongly correlated with signatures of indirect selection, and that evolutionary changes in recombination rate between species have observable impacts on this relationship. Conversely, signatures of direct selection on coding sequences show little to no relationship with recombination rate, even when restricted to genes where recombination rate is conserved between species. Thus, using measures of indirect and direct selection that bridge micro- and macro-evolutionary timescales, we demonstrate that the role of recombination rate and its dynamics varies for different signatures of selection.
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Affiliation(s)
- Madeline A Chase
- Department of Ecology and Genetics, Uppsala University, 75236 Uppsala, Sweden
- Swiss Ornithological Institute, 6204 Sempach, Switzerland
| | - Maurine Vilcot
- Department of Ecology and Genetics, Uppsala University, 75236 Uppsala, Sweden
- CEFE, University of Montpellier, CNRS, EPHE, IRD, 34293 Montpellier 5, France
| | - Carina F Mugal
- Department of Ecology and Genetics, Uppsala University, 75236 Uppsala, Sweden
- Laboratory of Biometry and Evolutionary Biology, University of Lyon 1, CNRS UMR 5558, 69622 Villeurbanne cedex, France
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2
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Schield DR, Perry BW, Adams RH, Holding ML, Nikolakis ZL, Gopalan SS, Smith CF, Parker JM, Meik JM, DeGiorgio M, Mackessy SP, Castoe TA. The roles of balancing selection and recombination in the evolution of rattlesnake venom. Nat Ecol Evol 2022; 6:1367-1380. [PMID: 35851850 PMCID: PMC9888523 DOI: 10.1038/s41559-022-01829-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Accepted: 06/15/2022] [Indexed: 02/02/2023]
Abstract
The origin of snake venom involved duplication and recruitment of non-venom genes into venom systems. Several studies have predicted that directional positive selection has governed this process. Venom composition varies substantially across snake species and venom phenotypes are locally adapted to prey, leading to coevolutionary interactions between predator and prey. Venom origins and contemporary snake venom evolution may therefore be driven by fundamentally different selection regimes, yet investigations of population-level patterns of selection have been limited. Here, we use whole-genome data from 68 rattlesnakes to test hypotheses about the factors that drive genomic diversity and differentiation in major venom gene regions. We show that selection has resulted in long-term maintenance of genetic diversity within and between species in multiple venom gene families. Our findings are inconsistent with a dominant role of directional positive selection and instead support a role of long-term balancing selection in shaping venom evolution. We also detect rapid decay of linkage disequilibrium due to high recombination rates in venom regions, suggesting that venom genes have reduced selective interference with nearby loci, including other venom paralogues. Our results provide an example of long-term balancing selection that drives trans-species polymorphism and help to explain how snake venom keeps pace with prey resistance.
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Affiliation(s)
- Drew R Schield
- Department of Biology, University of Texas at Arlington, Arlington, TX, USA.
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA.
| | - Blair W Perry
- Department of Biology, University of Texas at Arlington, Arlington, TX, USA
- School of Biological Sciences, Washington State University, Pullman, WA, USA
| | - Richard H Adams
- Department of Biological and Environmental Sciences, Georgia College and State University, Milledgeville, GA, USA
| | | | | | | | - Cara F Smith
- School of Biological Sciences, University of Northern Colorado, Greeley, CO, USA
| | - Joshua M Parker
- Life Science Department, Fresno City College, Fresno, CA, USA
| | - Jesse M Meik
- Department of Biological Sciences, Tarleton State University, Stephenville, TX, USA
| | - Michael DeGiorgio
- Department of Electrical Engineering and Computer Science, Florida Atlantic University, Boca Raton, FL, USA
| | - Stephen P Mackessy
- School of Biological Sciences, University of Northern Colorado, Greeley, CO, USA
| | - Todd A Castoe
- Department of Biology, University of Texas at Arlington, Arlington, TX, USA.
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3
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Pettie N, Llopart A, Comeron JM. Meiotic, genomic and evolutionary properties of crossover distribution in Drosophila yakuba. PLoS Genet 2022; 18:e1010087. [PMID: 35320272 PMCID: PMC8979470 DOI: 10.1371/journal.pgen.1010087] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Revised: 04/04/2022] [Accepted: 02/09/2022] [Indexed: 12/14/2022] Open
Abstract
The number and location of crossovers across genomes are highly regulated during meiosis, yet the key components controlling them are fast evolving, hindering our understanding of the mechanistic causes and evolutionary consequences of changes in crossover rates. Drosophila melanogaster has been a model species to study meiosis for more than a century, with an available high-resolution crossover map that is, nonetheless, missing for closely related species, thus preventing evolutionary context. Here, we applied a novel and highly efficient approach to generate whole-genome high-resolution crossover maps in D. yakuba to tackle multiple questions that benefit from being addressed collectively within an appropriate phylogenetic framework, in our case the D. melanogaster species subgroup. The genotyping of more than 1,600 individual meiotic events allowed us to identify several key distinct properties relative to D. melanogaster. We show that D. yakuba, in addition to higher crossover rates than D. melanogaster, has a stronger centromere effect and crossover assurance than any Drosophila species analyzed to date. We also report the presence of an active crossover-associated meiotic drive mechanism for the X chromosome that results in the preferential inclusion in oocytes of chromatids with crossovers. Our evolutionary and genomic analyses suggest that the genome-wide landscape of crossover rates in D. yakuba has been fairly stable and captures a significant signal of the ancestral crossover landscape for the whole D. melanogaster subgroup, even informative for the D. melanogaster lineage. Contemporary crossover rates in D. melanogaster, on the other hand, do not recapitulate ancestral crossovers landscapes. As a result, the temporal stability of crossover landscapes observed in D. yakuba makes this species an ideal system for applying population genetic models of selection and linkage, given that these models assume temporal constancy in linkage effects. Our studies emphasize the importance of generating multiple high-resolution crossover rate maps within a coherent phylogenetic context to broaden our understanding of crossover control during meiosis and to improve studies on the evolutionary consequences of variable crossover rates across genomes and time.
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Affiliation(s)
- Nikale Pettie
- Interdisciplinary Program in Genetics, University of Iowa, Iowa City, Iowa, United States of America
| | - Ana Llopart
- Interdisciplinary Program in Genetics, University of Iowa, Iowa City, Iowa, United States of America
- Department of Biology, University of Iowa, Iowa City, Iowa, United States of America
| | - Josep M. Comeron
- Interdisciplinary Program in Genetics, University of Iowa, Iowa City, Iowa, United States of America
- Department of Biology, University of Iowa, Iowa City, Iowa, United States of America
- * E-mail:
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4
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Edvardsen RB, Wallerman O, Furmanek T, Kleppe L, Jern P, Wallberg A, Kjærner-Semb E, Mæhle S, Olausson SK, Sundström E, Harboe T, Mangor-Jensen R, Møgster M, Perrichon P, Norberg B, Rubin CJ. Heterochiasmy and the establishment of gsdf as a novel sex determining gene in Atlantic halibut. PLoS Genet 2022; 18:e1010011. [PMID: 35134055 PMCID: PMC8824383 DOI: 10.1371/journal.pgen.1010011] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2021] [Accepted: 12/22/2021] [Indexed: 01/29/2023] Open
Abstract
Atlantic Halibut (Hippoglossus hippoglossus) has a X/Y genetic sex determination system, but the sex determining factor is not known. We produced a high-quality genome assembly from a male and identified parts of chromosome 13 as the Y chromosome due to sequence divergence between sexes and segregation of sex genotypes in pedigrees. Linkage analysis revealed that all chromosomes exhibit heterochiasmy, i.e. male-only and female-only meiotic recombination regions (MRR/FRR). We show that FRR/MRR intervals differ in nucleotide diversity and repeat class content and that this is true also for other Pleuronectidae species. We further show that remnants of a Gypsy-like transposable element insertion on chr13 promotes early male specific expression of gonadal somatic cell derived factor (gsdf). Less than 4.5 MYA, this male-determining element evolved on an autosomal FRR segment featuring pre-existing male meiotic recombination barriers, thereby creating a Y chromosome. Our findings indicate that heterochiasmy may facilitate the evolution of genetic sex determination systems relying on linkage of sexually antagonistic loci to a sex-determining factor. Even closely related fish species can have different sex chromosomes, but this turn-over of sex determination systems is poorly understood. Here, we used large-scale genome sequencing to determine the DNA sequence of the Atlantic halibut chromosomes and compared sequencing data from males and females to identify the sex chromosomes. We show that males have much higher gene activity of the gene gonadal somatic cell derived factor (gsdf), which is located on the sex chromosomes and has a role in testicular development. The genome contains many mobile DNA sequences, transposable elements (TEs), one placed in front of gsdf, enhancing its activity. This made gsdf the sex determining factor, thereby creating a new Y-chromosome. We further describe how all Atlantic halibut chromosomes behave similar to sex chromosomes in that most regions only recombine in one sex. This phenomenon may contribute to the rapid turn-over of genetic sex determination systems in fish. Our results highlight the molecular events creating a new Y-chromosome and show that the new Atlantic halibut Y was formed less than 4.5 million years ago. Future studies in Atlantic halibut and closely related species can shed light on mechanisms contributing to sex chromosome evolution in fish.
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Affiliation(s)
| | | | | | - Lene Kleppe
- Institute of Marine Research, Bergen, Norway
| | | | | | | | - Stig Mæhle
- Institute of Marine Research, Bergen, Norway
| | | | | | | | | | | | | | | | - Carl-Johan Rubin
- Institute of Marine Research, Bergen, Norway
- Uppsala University, Uppsala, Sweden
- * E-mail: (RBE); (C-JR)
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5
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Dukić M, Bomblies K. Male and female recombination landscapes of diploid Arabidopsis arenosa. Genetics 2022; 220:6499271. [PMID: 35100396 PMCID: PMC8893250 DOI: 10.1093/genetics/iyab236] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Accepted: 12/17/2021] [Indexed: 12/13/2022] Open
Abstract
Abstract
The number and placement of meiotic crossover events during meiosis have important implications for the fidelity of chromosome segregation as well as patterns of inheritance. Despite the functional importance of recombination, recombination landscapes vary widely among and within species, and this can have a strong impact on evolutionary processes. A good knowledge of recombination landscapes is important for model systems in evolutionary and ecological genetics, since it can improve interpretation of genomic patterns of differentiation and genome evolution, and provides an important starting point for understanding the causes and consequences of recombination rate variation. Arabidopsis arenosa is a powerful evolutionary genetic model for studying the molecular basis of adaptation and recombination rate evolution. Here, we generate genetic maps for 2 diploid A. arenosa individuals from distinct genetic lineages where we have prior knowledge that meiotic genes show evidence of selection. We complement the genetic maps with cytological approaches to map and quantify recombination rates, and test the idea that these populations might have distinct patterns of recombination. We explore how recombination differs at the level of populations, individuals, sexes and genomic regions. We show that the positioning of crossovers along a chromosome correlates with their number, presumably a consequence of crossover interference, and discuss how this effect can cause differences in recombination landscape among sexes or species. We identify several instances of female segregation distortion. We found that averaged genome-wide recombination rate is lower and sex differences subtler in A. arenosa than in Arabidopsis thaliana.
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Affiliation(s)
- Marinela Dukić
- Department of Biology, Plant Evolutionary Genetics, Institute of Plant Molecular Biology, ETH Zürich, Zürich 8092, Switzerland
| | - Kirsten Bomblies
- Department of Biology, Plant Evolutionary Genetics, Institute of Plant Molecular Biology, ETH Zürich, Zürich 8092, Switzerland
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6
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Korunes KL, Myers RB, Hardy R, Noor MAF. PseudoBase: a genomic visualization and exploration resource for the Drosophila pseudoobscura subgroup. Fly (Austin) 2021; 15:38-44. [PMID: 33319644 PMCID: PMC7808432 DOI: 10.1080/19336934.2020.1864201] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Revised: 12/08/2020] [Accepted: 12/10/2020] [Indexed: 10/22/2022] Open
Abstract
Drosophila pseudoobscura is a classic model system for the study of evolutionary genetics and genomics. Given this long-standing interest, many genome sequences have accumulated for D. pseudoobscura and closely related species D. persimilis, D. miranda, and D. lowei. To facilitate the exploration of genetic variation within species and comparative genomics across species, we present PseudoBase, a database that couples extensive publicly available genomic data with simple visualization and query tools via an intuitive graphical interface, amenable for use in both research and educational settings. All genetic variation (SNPs and indels) within the database is derived from the same workflow, so variants are easily comparable across data sets. Features include an embedded JBrowse interface, ability to pull out alignments of individual genes/regions, and batch access for gene lists. Here, we introduce PseudoBase, and we demonstrate how this resource facilitates use of extensive genomic data from flies of the Drosophila pseudoobscura subgroup.
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Affiliation(s)
| | | | - Ryan Hardy
- Biology Department, Duke University, Durham, NC, USA
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7
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Gompert Z, Feder JL, Nosil P. Natural selection drives genome-wide evolution via chance genetic associations. Mol Ecol 2021; 31:467-481. [PMID: 34704650 DOI: 10.1111/mec.16247] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2021] [Revised: 10/13/2021] [Accepted: 10/15/2021] [Indexed: 11/29/2022]
Abstract
Understanding selection's impact on the genome is a major theme in biology. Functionally neutral genetic regions can be affected indirectly by natural selection, via their statistical association with genes under direct selection. The genomic extent of such indirect selection, particularly across loci not physically linked to those under direct selection, remains poorly understood, as does the time scale at which indirect selection occurs. Here, we use field experiments and genomic data in stick insects, deer mice and stickleback fish to show that widespread statistical associations with genes known to affect fitness cause many genetic loci across the genome to be impacted indirectly by selection. This includes regions physically distant from those directly under selection. Then, focusing on the stick insect system, we show that statistical associations between SNPs and other unknown, causal variants result in additional indirect selection in general and specifically within genomic regions of physically linked loci. This widespread indirect selection necessarily makes aspects of evolution more predictable. Thus, natural selection combines with chance genetic associations to affect genome-wide evolution across linked and unlinked loci and even in modest-sized populations. This process has implications for the application of evolutionary principles in basic and applied science.
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Affiliation(s)
- Zachariah Gompert
- Department of Biology, Utah State University, Logan, Utah, USA.,Ecology Center, Utah State University, Logan, Utah, USA
| | - Jeffrey L Feder
- Department of Biological Sciences, University of Notre Dame, Notre Dame, Indiana, USA
| | - Patrik Nosil
- CEFE, Univ Montpellier, CNRS, EPHE, IRD, Univ Paul Valéry Montpellier 3, Montpellier, France
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8
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Korunes KL, Machado CA, Noor MAF. Inversions shape the divergence of Drosophila pseudoobscura and Drosophila persimilis on multiple timescales. Evolution 2021; 75:1820-1834. [PMID: 34041743 DOI: 10.1111/evo.14278] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2020] [Revised: 05/03/2021] [Accepted: 05/17/2021] [Indexed: 02/02/2023]
Abstract
By shaping meiotic recombination, chromosomal inversions can influence genetic exchange between hybridizing species. Despite the recognized importance of inversions in evolutionary processes such as divergence and speciation, teasing apart the effects of inversions over time remains challenging. For example, are their effects on sequence divergence primarily generated through creating blocks of linkage disequilibrium prespeciation or through preventing gene flux after speciation? We provide a comprehensive look into the influence of inversions on gene flow throughout the evolutionary history of a classic system: Drosophila pseudoobscura and Drosophila persimilis. We use extensive whole-genome sequence data to report patterns of introgression and divergence with respect to chromosomal arrangements. Overall, we find evidence that inversions have contributed to divergence patterns between D. pseudoobscura and D. persimilis over three distinct timescales: (1) segregation of ancestral polymorphism early in the speciation process, (2) gene flow after the split of D. pseudoobscura and D. persimilis, but prior to the split of D. pseudoobscura subspecies, and (3) recent gene flow between sympatric D. pseudoobscura and D. persimilis, after the split of D. pseudoobscura subspecies. We discuss these results in terms of our understanding of evolution in this classic system and provide cautions for interpreting divergence measures in other systems.
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Affiliation(s)
- Katharine L Korunes
- Department of Evolutionary Anthropology, Duke University, Durham, North Carolina, 27708
| | - Carlos A Machado
- Department of Biology, University of Maryland, College Park, Maryland, 20742
| | - Mohamed A F Noor
- Department of Biology, Duke University, Durham, North Carolina, 27708
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9
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Schield DR, Pasquesi GIM, Perry BW, Adams RH, Nikolakis ZL, Westfall AK, Orton RW, Meik JM, Mackessy SP, Castoe TA. Snake Recombination Landscapes Are Concentrated in Functional Regions despite PRDM9. Mol Biol Evol 2021; 37:1272-1294. [PMID: 31926008 DOI: 10.1093/molbev/msaa003] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Meiotic recombination in vertebrates is concentrated in hotspots throughout the genome. The location and stability of hotspots have been linked to the presence or absence of PRDM9, leading to two primary models for hotspot evolution derived from mammals and birds. Species with PRDM9-directed recombination have rapid turnover of hotspots concentrated in intergenic regions (i.e., mammals), whereas hotspots in species lacking PRDM9 are concentrated in functional regions and have greater stability over time (i.e., birds). Snakes possess PRDM9, yet virtually nothing is known about snake recombination. Here, we examine the recombination landscape and test hypotheses about the roles of PRDM9 in rattlesnakes. We find substantial variation in recombination rate within and among snake chromosomes, and positive correlations between recombination rate and gene density, GC content, and genetic diversity. Like mammals, snakes appear to have a functional and active PRDM9, but rather than being directed away from genes, snake hotspots are concentrated in promoters and functional regions-a pattern previously associated only with species that lack a functional PRDM9. Snakes therefore provide a unique example of recombination landscapes in which PRDM9 is functional, yet recombination hotspots are associated with functional genic regions-a combination of features that defy existing paradigms for recombination landscapes in vertebrates. Our findings also provide evidence that high recombination rates are a shared feature of vertebrate microchromosomes. Our results challenge previous assumptions about the adaptive role of PRDM9 and highlight the diversity of recombination landscape features among vertebrate lineages.
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Affiliation(s)
- Drew R Schield
- Department of Biology, University of Texas at Arlington, Arlington, TX
| | | | - Blair W Perry
- Department of Biology, University of Texas at Arlington, Arlington, TX
| | - Richard H Adams
- Department of Biology, University of Texas at Arlington, Arlington, TX.,Department of Computer & Electrical Engineering and Computer Science, Florida Atlantic University, Boca Raton, FL
| | | | | | - Richard W Orton
- Department of Biology, University of Texas at Arlington, Arlington, TX
| | - Jesse M Meik
- Department of Biological Sciences, Tarleton State University, Stephenville, TX
| | - Stephen P Mackessy
- School of Biological Sciences, University of Northern Colorado, Greeley, CO
| | - Todd A Castoe
- Department of Biology, University of Texas at Arlington, Arlington, TX
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10
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Ma F, Lau CY, Zheng C. Large genetic diversity and strong positive selection in F-box and GPCR genes among the wild isolates of Caenorhabditis elegans. Genome Biol Evol 2021; 13:6163285. [PMID: 33693740 PMCID: PMC8120010 DOI: 10.1093/gbe/evab048] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 02/17/2021] [Accepted: 03/03/2021] [Indexed: 01/05/2023] Open
Abstract
The F-box and chemosensory GPCR (csGPCR) gene families are greatly expanded in nematodes, including the model organism Caenorhabditis elegans, compared with insects and vertebrates. However, the intraspecific evolution of these two gene families in nematodes remain unexamined. In this study, we analyzed the genomic sequences of 330 recently sequenced wild isolates of C. elegans using a range of population genetics approaches. We found that F-box and csGPCR genes, especially the Srw family csGPCRs, showed much more diversity than other gene families. Population structure analysis and phylogenetic analysis divided the wild strains into eight non-Hawaiian and three Hawaiian subpopulations. Some Hawaiian strains appeared to be more ancestral than all other strains. F-box and csGPCR genes maintained a great amount of the ancestral variants in the Hawaiian subpopulation and their divergence among the non-Hawaiian subpopulations contributed significantly to population structure. F-box genes are mostly located at the chromosomal arms and high recombination rate correlates with their large polymorphism. Moreover, using both neutrality tests and extended haplotype homozygosity analysis, we identified signatures of strong positive selection in the F-box and csGPCR genes among the wild isolates, especially in the non-Hawaiian population. Accumulation of high-frequency-derived alleles in these genes was found in non-Hawaiian population, leading to divergence from the ancestral genotype. In summary, we found that F-box and csGPCR genes harbor a large pool of natural variants, which may be subjected to positive selection. These variants are mostly mapped to the substrate-recognition domains of F-box proteins and the extracellular and intracellular regions of csGPCRs, possibly resulting in advantages during adaptation by affecting protein degradation and the sensing of environmental cues, respectively.
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Affiliation(s)
- Fuqiang Ma
- School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China
| | - Chun Yin Lau
- School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China
| | - Chaogu Zheng
- School of Biological Sciences, The University of Hong Kong, Hong Kong SAR, China
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11
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Schrider DR. Background Selection Does Not Mimic the Patterns of Genetic Diversity Produced by Selective Sweeps. Genetics 2020; 216:499-519. [PMID: 32847814 PMCID: PMC7536861 DOI: 10.1534/genetics.120.303469] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2019] [Accepted: 08/04/2020] [Indexed: 12/28/2022] Open
Abstract
It is increasingly evident that natural selection plays a prominent role in shaping patterns of diversity across the genome. The most commonly studied modes of natural selection are positive selection and negative selection, which refer to directional selection for and against derived mutations, respectively. Positive selection can result in hitchhiking events, in which a beneficial allele rapidly replaces all others in the population, creating a valley of diversity around the selected site along with characteristic skews in allele frequencies and linkage disequilibrium among linked neutral polymorphisms. Similarly, negative selection reduces variation not only at selected sites but also at linked sites, a phenomenon called background selection (BGS). Thus, discriminating between these two forces may be difficult, and one might expect efforts to detect hitchhiking to produce an excess of false positives in regions affected by BGS. Here, we examine the similarity between BGS and hitchhiking models via simulation. First, we show that BGS may somewhat resemble hitchhiking in simplistic scenarios in which a region constrained by negative selection is flanked by large stretches of unconstrained sites, echoing previous results. However, this scenario does not mirror the actual spatial arrangement of selected sites across the genome. By performing forward simulations under more realistic scenarios of BGS, modeling the locations of protein-coding and conserved noncoding DNA in real genomes, we show that the spatial patterns of variation produced by BGS rarely mimic those of hitchhiking events. Indeed, BGS is not substantially more likely than neutrality to produce false signatures of hitchhiking. This holds for simulations modeled after both humans and Drosophila, and for several different demographic histories. These results demonstrate that appropriately designed scans for hitchhiking need not consider BGS's impact on false-positive rates. However, we do find evidence that BGS increases the false-negative rate for hitchhiking, an observation that demands further investigation.
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Affiliation(s)
- Daniel R Schrider
- Department of Genetics, University of North Carolina, Chapel Hill, North Carolina 27514
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12
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Fuller ZL, Koury SA, Leonard CJ, Young RE, Ikegami K, Westlake J, Richards S, Schaeffer SW, Phadnis N. Extensive Recombination Suppression and Epistatic Selection Causes Chromosome-Wide Differentiation of a Selfish Sex Chromosome in Drosophila pseudoobscura. Genetics 2020; 216:205-226. [PMID: 32732371 PMCID: PMC7463281 DOI: 10.1534/genetics.120.303460] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2020] [Accepted: 07/27/2020] [Indexed: 11/18/2022] Open
Abstract
Sex-Ratio (SR) chromosomes are selfish X-chromosomes that distort Mendelian segregation and are commonly associated with inversions. These chromosomal rearrangements suppress recombination with Standard (ST) X-chromosomes and are hypothesized to maintain multiple alleles important for distortion in a single large haplotype. Here, we conduct a multifaceted study of the multiply inverted Drosophila pseudoobscura SR chromosome to understand the evolutionary history, genetic architecture, and present-day dynamics that shape this enigmatic selfish chromosome. The D. pseudoobscura SR chromosome has three nonoverlapping inversions of the right arm of the metacentric X-chromosome: basal, medial, and terminal. We find that 23 of 29 Mb of the D. pseudoobscuraX-chromosome right arm is highly differentiated between the Standard and SR arrangements, including a 6.6 Mb collinear region between the medial and terminal inversions. Although crossing-over is heavily suppressed on this chromosome arm, we discover it is not completely eliminated, with measured rates indicating recombination suppression alone cannot explain patterns of differentiation or the near-perfect association of the three SR chromosome inversions in nature. We then demonstrate the ancient basal and medial inversions of the SR chromosome contain genes sufficient to cause weak distortion. In contrast, the younger terminal inversion cannot distort by itself, but contains at least one modifier gene necessary for full manifestation of strong sex chromosome distortion. By parameterizing population genetic models for chromosome-wide linkage disequilibrium with our experimental results, we infer that strong selection acts to maintain the near-perfect association of SR chromosome inversions in present-day populations. Based on comparative genomic analyses, direct recombination experiments, segregation distortion assays, and population genetic modeling, we conclude the combined action of suppressed recombination and strong, ongoing, epistatic selection shape the D. pseudoobscura SR arrangement into a highly differentiated chromosome.
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Affiliation(s)
- Zachary L Fuller
- Department of Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
- Department of Biological Sciences, Columbia University, New York, New York 10027
| | - Spencer A Koury
- School of Biological Sciences, University of Utah, Salt Lake City, Utah 84112
| | | | - Randee E Young
- School of Biological Sciences, University of Utah, Salt Lake City, Utah 84112
- Department of Genetics, University of Wisconsin, Madison, Wisconsin 53706
| | - Kobe Ikegami
- School of Biological Sciences, University of Utah, Salt Lake City, Utah 84112
| | - Jonathan Westlake
- Department of Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
| | - Stephen Richards
- Human Genome Sequencing Center, Baylor College of Medicine, 1 Baylor Plaza, Houston, Texas 77030
| | - Stephen W Schaeffer
- Department of Biology, The Pennsylvania State University, University Park, Pennsylvania 16802
| | - Nitin Phadnis
- School of Biological Sciences, University of Utah, Salt Lake City, Utah 84112
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13
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From molecules to populations: appreciating and estimating recombination rate variation. Nat Rev Genet 2020; 21:476-492. [DOI: 10.1038/s41576-020-0240-1] [Citation(s) in RCA: 45] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/15/2020] [Indexed: 02/07/2023]
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14
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The Intracellular Symbiont Wolbachia pipientis Enhances Recombination in a Dose-Dependent Manner. INSECTS 2020; 11:insects11050284. [PMID: 32384776 PMCID: PMC7290356 DOI: 10.3390/insects11050284] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/14/2020] [Revised: 04/24/2020] [Accepted: 04/27/2020] [Indexed: 02/07/2023]
Abstract
Wolbachia pipientis is an intracellular alphaproteobacterium that infects 40%-60% of insect species and is well known for host reproductive manipulations. Although Wolbachia are primarily maternally transmitted, evidence of horizontal transmission can be found in incongruent host-symbiont phylogenies and recent acquisitions of the same Wolbachia strain by distantly related species. Parasitoids and predator-prey interactions may indeed facilitate the transfer of Wolbachia between insect lineages, but it is likely that Wolbachia are acquired via introgression in many cases. Many hypotheses exist to explain Wolbachia prevalence and penetrance, such as nutritional supplementation, protection from parasites, protection from viruses, or direct reproductive parasitism. Using classical genetics, we show that Wolbachia increase recombination in infected lineages across two genomic intervals. This increase in recombination is titer-dependent as the wMelPop variant, which infects at higher load in Drosophila melanogaster, increases recombination 5% more than the wMel variant. In addition, we also show that Spiroplasma poulsonii, another bacterial intracellular symbiont of D. melanogaster, does not induce an increase in recombination. Our results suggest that Wolbachia infection specifically alters its host's recombination landscape in a dose-dependent manner.
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15
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Woerner AE, Veeramah KR, Watkins JC, Hammer MF. The Role of Phylogenetically Conserved Elements in Shaping Patterns of Human Genomic Diversity. Mol Biol Evol 2020; 35:2284-2295. [PMID: 30113695 DOI: 10.1093/molbev/msy145] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Evolutionary genetic studies have shown a positive correlation between levels of nucleotide diversity and either rates of recombination or genetic distance to genes. Both positive-directional and purifying selection have been offered as the source of these correlations via genetic hitchhiking and background selection, respectively. Phylogenetically conserved elements (CEs) are short (∼100 bp), widely distributed (comprising ∼5% of genome), sequences that are often found far from genes. While the function of many CEs is unknown, CEs also are associated with reduced diversity at linked sites. Using high coverage (>80×) whole genome data from two human populations, the Yoruba and the CEU, we perform fine scale evaluations of diversity, rates of recombination, and linkage to genes. We find that the local rate of recombination has a stronger effect on levels of diversity than linkage to genes, and that these effects of recombination persist even in regions far from genes. Our whole genome modeling demonstrates that, rather than recombination or GC-biased gene conversion, selection on sites within or linked to CEs better explains the observed genomic diversity patterns. A major implication is that very few sites in the human genome are predicted to be free of the effects of selection. These sites, which we refer to as the human "neutralome," comprise only 1.2% of the autosomes and 5.1% of the X chromosome. Demographic analysis of the neutralome reveals larger population sizes and lower rates of growth for ancestral human populations than inferred by previous analyses.
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Affiliation(s)
- August E Woerner
- ARL Division of Biotechnology, University of Arizona, Tucson, AZ.,Center for Human Identification, University of North Texas Health Science Center, Fort Worth, TX
| | - Krishna R Veeramah
- Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY
| | | | - Michael F Hammer
- ARL Division of Biotechnology, University of Arizona, Tucson, AZ
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16
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da Silva VH, Laine VN, Bosse M, Spurgin LG, Derks MFL, van Oers K, Dibbits B, Slate J, Crooijmans RPMA, Visser ME, Groenen MAM. The Genomic Complexity of a Large Inversion in Great Tits. Genome Biol Evol 2020; 11:1870-1881. [PMID: 31114855 PMCID: PMC6609730 DOI: 10.1093/gbe/evz106] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/16/2019] [Indexed: 12/11/2022] Open
Abstract
Chromosome inversions have clear effects on genome evolution and have been associated with speciation, adaptation, and the evolution of the sex chromosomes. In birds, these inversions may play an important role in hybridization of species and disassortative mating. We identified a large (≈64 Mb) inversion polymorphism in the great tit (Parus major) that encompasses almost 1,000 genes and more than 90% of Chromosome 1A. The inversion occurs at a low frequency in a set of over 2,300 genotyped great tits in the Netherlands with only 5% of the birds being heterozygous for the inversion. In an additional analysis of 29 resequenced birds from across Europe, we found two heterozygotes. The likely inversion breakpoints show considerable genomic complexity, including multiple copy number variable segments. We identified different haplotypes for the inversion, which differ in the degree of recombination in the center of the chromosome. Overall, this remarkable genetic variant is widespread among distinct great tit populations and future studies of the inversion haplotype, including how it affects the fitness of carriers, may help to understand the mechanisms that maintain it.
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Affiliation(s)
- Vinicius H da Silva
- Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands.,Department of Animal Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands.,Swedish University of Agricultural Sciences (SLU), Uppsala, Sweden
| | - Veronika N Laine
- Department of Molecular and Cellular Biology, Harvard University
| | - Mirte Bosse
- Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands
| | - Lewis G Spurgin
- School of Biological Sciences, University of East Anglia, Norwich Research Park University of East Anglia, Norwich, United Kingdom
| | - Martijn F L Derks
- Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands
| | - Kees van Oers
- Department of Animal Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands
| | - Bert Dibbits
- Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands
| | - Jon Slate
- Department of Animal and Plant Sciences, The University of Sheffield, Sheffield, United Kingdom
| | | | - Marcel E Visser
- Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands.,Department of Animal Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands
| | - Martien A M Groenen
- Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands
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17
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Li Z, Löytynoja A, Fraimout A, Merilä J. Effects of marker type and filtering criteria on Q ST- F ST comparisons. ROYAL SOCIETY OPEN SCIENCE 2019; 6:190666. [PMID: 31827824 PMCID: PMC6894560 DOI: 10.1098/rsos.190666] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Accepted: 09/16/2019] [Indexed: 06/10/2023]
Abstract
Comparative studies of quantitative and neutral genetic differentiation (Q ST-F ST tests) provide means to detect adaptive population differentiation. However, Q ST-F ST tests can be overly liberal if the markers used deflate F ST below its expectation, or overly conservative if methodological biases lead to inflated F ST estimates. We investigated how marker type and filtering criteria for marker selection influence Q ST-F ST comparisons through their effects on F ST using simulations and empirical data on over 18 000 in silico genotyped microsatellites and 3.8 million single-locus polymorphism (SNP) loci from four populations of nine-spined sticklebacks (Pungitius pungitius). Empirical and simulated data revealed that F ST decreased with increasing marker variability, and was generally higher with SNPs than with microsatellites. The estimated baseline F ST levels were also sensitive to filtering criteria for SNPs: both minor alleles and linkage disequilibrium (LD) pruning influenced F ST estimation, as did marker ascertainment. However, in the case of stickleback data used here where Q ST is high, the choice of marker type, their genomic location, ascertainment and filtering made little difference to outcomes of Q ST-F ST tests. Nevertheless, we recommend that Q ST-F ST tests using microsatellites should discard the most variable loci, and those using SNPs should pay attention to marker ascertainment and properly account for LD before filtering SNPs. This may be especially important when level of quantitative trait differentiation is low and levels of neutral differentiation high.
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Affiliation(s)
- Zitong Li
- Ecological Genetics Research Unit, Organismal and Evolutionary Biology Research Programme, University of Helsinki, Helsinki 00014, Finland
| | - Ari Löytynoja
- Institute of Biotechnology, University of Helsinki, Helsinki 00014, Finland
| | - Antoine Fraimout
- Ecological Genetics Research Unit, Organismal and Evolutionary Biology Research Programme, University of Helsinki, Helsinki 00014, Finland
| | - Juha Merilä
- Ecological Genetics Research Unit, Organismal and Evolutionary Biology Research Programme, University of Helsinki, Helsinki 00014, Finland
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18
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Konrad A, Brady MJ, Bergthorsson U, Katju V. Mutational Landscape of Spontaneous Base Substitutions and Small Indels in Experimental Caenorhabditis elegans Populations of Differing Size. Genetics 2019; 212:837-854. [PMID: 31110155 PMCID: PMC6614903 DOI: 10.1534/genetics.119.302054] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2019] [Accepted: 05/16/2019] [Indexed: 02/08/2023] Open
Abstract
Experimental investigations into the rates and fitness effects of spontaneous mutations are fundamental to our understanding of the evolutionary process. To gain insights into the molecular and fitness consequences of spontaneous mutations, we conducted a mutation accumulation (MA) experiment at varying population sizes in the nematode Caenorhabditis elegans, evolving 35 lines in parallel for 409 generations at three population sizes (N = 1, 10, and 100 individuals). Here, we focus on nuclear SNPs and small insertion/deletions (indels) under minimal influence of selection, as well as their accrual rates in larger populations under greater selection efficacy. The spontaneous rates of base substitutions and small indels are 1.84 (95% C.I. ± 0.14) × 10-9 substitutions and 6.84 (95% C.I. ± 0.97) × 10-10 changes/site/generation, respectively. Small indels exhibit a deletion bias with deletions exceeding insertions by threefold. Notably, there was no correlation between the frequency of base substitutions, nonsynonymous substitutions, or small indels with population size. These results contrast with our previous analysis of mitochondrial DNA mutations and nuclear copy-number changes in these MA lines, and suggest that nuclear base substitutions and small indels are under less stringent purifying selection compared to the former mutational classes. A transition bias was observed in exons as was a near universal base substitution bias toward A/T. Strongly context-dependent base substitutions, where 5'-Ts and 3'-As increase the frequency of A/T → T/A transversions, especially at the boundaries of A or T homopolymeric runs, manifest as higher mutation rates in (i) introns and intergenic regions relative to exons, (ii) chromosomal cores vs. arms and tips, and (iii) germline-expressed genes.
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Affiliation(s)
- Anke Konrad
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, Texas 77845
| | - Meghan J Brady
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, Texas 77845
| | - Ulfar Bergthorsson
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, Texas 77845
| | - Vaishali Katju
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, Texas 77845
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19
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Crysnanto D, Obbard DJ. Widespread gene duplication and adaptive evolution in the RNA interference pathways of the Drosophila obscura group. BMC Evol Biol 2019; 19:99. [PMID: 31068148 PMCID: PMC6505081 DOI: 10.1186/s12862-019-1425-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Accepted: 04/18/2019] [Indexed: 12/15/2022] Open
Abstract
BACKGROUND RNA interference (RNAi) related pathways provide defense against viruses and transposable elements, and have been implicated in the suppression of meiotic drive elements. Genes in these pathways often exhibit high levels of adaptive substitution, and over longer timescales show gene duplication and loss-most likely as a consequence of their role in mediating conflict with these parasites. This is particularly striking for Argonaute 2 (Ago2), which is ancestrally the key effector of antiviral RNAi in insects, but has repeatedly formed new testis-specific duplicates in the recent history of the obscura species-group of Drosophila. RESULTS Here we take advantage of publicly available genomic and transcriptomic data to identify six further RNAi-pathway genes that have duplicated in this clade of Drosophila, and examine their evolutionary history. As seen for Ago2, we observe high levels of adaptive amino-acid substitution and changes in sex-biased expression in many of the paralogs. However, our phylogenetic analysis suggests that co-duplications of the RNAi machinery were not synchronous, and our expression analysis fails to identify consistent male-specific expression. CONCLUSIONS These results confirm that RNAi genes, including genes of the antiviral and piRNA pathways, have undergone multiple independent duplications and that their history has been particularly labile within the obscura group. However, they also suggest that the selective pressures driving these changes have not been consistent, implying that more than one selective agent may be responsible.
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Affiliation(s)
- Danang Crysnanto
- Institute of Evolutionary Biology, University of Edinburgh, Charlotte Auerbach Road, Edinburgh, UK
- Animal Genomics, ETH Zurich, Zurich, Switzerland
| | - Darren J. Obbard
- Institute of Evolutionary Biology, University of Edinburgh, Charlotte Auerbach Road, Edinburgh, UK
- Centre for Infection, Evolution and Immunity, University of Edinburgh, Edinburgh, UK
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20
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Castillo DM, Moyle LC. Conspecific sperm precedence is reinforced, but postcopulatory sexual selection weakened, in sympatric populations of Drosophila. Proc Biol Sci 2019; 286:20182535. [PMID: 30900533 PMCID: PMC6452082 DOI: 10.1098/rspb.2018.2535] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2018] [Accepted: 03/06/2019] [Indexed: 12/21/2022] Open
Abstract
Sexual selection can accelerate speciation by driving the evolution of reproductive isolation, but forces driving speciation could also reciprocally feedback on sexual selection. This might be particularly important in the context of 'reinforcement', where selection acts directly to increase prezygotic barriers to reduce the cost of heterospecific matings. Using assays of sperm competition within and between two sister species, we show a signature of reinforcement where these species interact: populations of Drosophila pseudoobscura that co-occur with sister species D. persimilis have an elevated ability to outcompete heterospecific sperm, consistent with selection for increased postcopulatory isolation. We also find these D. pseudoobscura populations have decreased sperm competitive ability against conspecifics, reducing the opportunity for sexual selection within these populations. Our findings demonstrate that direct selection to increase reproductive isolation against other species can compromise the efficacy of sexual selection within species, a collateral effect of reproductive traits responding to heterospecific interactions.
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Affiliation(s)
- Dean M. Castillo
- Department of Biology, Indiana University, 1001 East Third Street, Bloomington, IN 47405, USA
- Department of Molecular Biology and Genetics, Cornell University, 526 Campus Road, Ithaca, NY 14853, USA
| | - Leonie C. Moyle
- Department of Biology, Indiana University, 1001 East Third Street, Bloomington, IN 47405, USA
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21
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Abstract
In this perspective, we evaluate the explanatory power of the neutral theory of molecular evolution, 50 years after its introduction by Kimura. We argue that the neutral theory was supported by unreliable theoretical and empirical evidence from the beginning, and that in light of modern, genome-scale data, we can firmly reject its universality. The ubiquity of adaptive variation both within and between species means that a more comprehensive theory of molecular evolution must be sought.
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Affiliation(s)
- Andrew D Kern
- Department of Genetics, Rutgers University, Piscataway, NJ
| | - Matthew W Hahn
- Department of Biology and Department of Computer Science, Indiana University Bloomington, IN
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22
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Katju V, Bergthorsson U. Old Trade, New Tricks: Insights into the Spontaneous Mutation Process from the Partnering of Classical Mutation Accumulation Experiments with High-Throughput Genomic Approaches. Genome Biol Evol 2019; 11:136-165. [PMID: 30476040 PMCID: PMC6330053 DOI: 10.1093/gbe/evy252] [Citation(s) in RCA: 70] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/22/2018] [Indexed: 12/17/2022] Open
Abstract
Mutations spawn genetic variation which, in turn, fuels evolution. Hence, experimental investigations into the rate and fitness effects of spontaneous mutations are central to the study of evolution. Mutation accumulation (MA) experiments have served as a cornerstone for furthering our understanding of spontaneous mutations for four decades. In the pregenomic era, phenotypic measurements of fitness-related traits in MA lines were used to indirectly estimate key mutational parameters, such as the genomic mutation rate, new mutational variance per generation, and the average fitness effect of mutations. Rapidly emerging next-generating sequencing technology has supplanted this phenotype-dependent approach, enabling direct empirical estimates of the mutation rate and a more nuanced understanding of the relative contributions of different classes of mutations to the standing genetic variation. Whole-genome sequencing of MA lines bears immense potential to provide a unified account of the evolutionary process at multiple levels-the genetic basis of variation, and the evolutionary dynamics of mutations under the forces of selection and drift. In this review, we have attempted to synthesize key insights into the spontaneous mutation process that are rapidly emerging from the partnering of classical MA experiments with high-throughput sequencing, with particular emphasis on the spontaneous rates and molecular properties of different mutational classes in nuclear and mitochondrial genomes of diverse taxa, the contribution of mutations to the evolution of gene expression, and the rate and stability of transgenerational epigenetic modifications. Future advances in sequencing technologies will enable greater species representation to further refine our understanding of mutational parameters and their functional consequences.
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Affiliation(s)
- Vaishali Katju
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843-4458
| | - Ulfar Bergthorsson
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX 77843-4458
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23
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Corcoran P, Gossmann TI, Barton HJ, Slate J, Zeng K. Determinants of the Efficacy of Natural Selection on Coding and Noncoding Variability in Two Passerine Species. Genome Biol Evol 2018; 9:2987-3007. [PMID: 29045655 PMCID: PMC5714183 DOI: 10.1093/gbe/evx213] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/16/2017] [Indexed: 02/06/2023] Open
Abstract
Population genetic theory predicts that selection should be more effective when the effective population size (Ne) is larger, and that the efficacy of selection should correlate positively with recombination rate. Here, we analyzed the genomes of ten great tits and ten zebra finches. Nucleotide diversity at 4-fold degenerate sites indicates that zebra finches have a 2.83-fold larger Ne. We obtained clear evidence that purifying selection is more effective in zebra finches. The proportion of substitutions at 0-fold degenerate sites fixed by positive selection (α) is high in both species (great tit 48%; zebra finch 64%) and is significantly higher in zebra finches. When α was estimated on GC-conservative changes (i.e., between A and T and between G and C), the estimates reduced in both species (great tit 22%; zebra finch 53%). A theoretical model presented herein suggests that failing to control for the effects of GC-biased gene conversion (gBGC) is potentially a contributor to the overestimation of α, and that this effect cannot be alleviated by first fitting a demographic model to neutral variants. We present the first estimates in birds for α in the untranslated regions, and found evidence for substantial adaptive changes. Finally, although purifying selection is stronger in high-recombination regions, we obtained mixed evidence for α increasing with recombination rate, especially after accounting for gBGC. These results highlight that it is important to consider the potential confounding effects of gBGC when quantifying selection and that our understanding of what determines the efficacy of selection is incomplete.
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Affiliation(s)
- Pádraic Corcoran
- Department of Animal and Plant Sciences, University of Sheffield, South Yorkshire, United Kingdom
| | - Toni I Gossmann
- Department of Animal and Plant Sciences, University of Sheffield, South Yorkshire, United Kingdom
| | - Henry J Barton
- Department of Animal and Plant Sciences, University of Sheffield, South Yorkshire, United Kingdom
| | | | - Jon Slate
- Department of Animal and Plant Sciences, University of Sheffield, South Yorkshire, United Kingdom
| | - Kai Zeng
- Department of Animal and Plant Sciences, University of Sheffield, South Yorkshire, United Kingdom
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24
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Abstract
Levels and patterns of genetic diversity can provide insights into a population’s history. In species with sex chromosomes, differences between genomic regions with unique inheritance patterns can be used to distinguish between different sets of possible demographic and selective events. This review introduces the differences in population history for sex chromosomes and autosomes, provides the expectations for genetic diversity across the genome under different evolutionary scenarios, and gives an introductory description for how deviations in these expectations are calculated and can be interpreted. Predominantly, diversity on the sex chromosomes has been used to explore and address three research areas: 1) Mating patterns and sex-biased variance in reproductive success, 2) signatures of selection, and 3) evidence for modes of speciation and introgression. After introducing the theory, this review catalogs recent studies of genetic diversity on the sex chromosomes across species within the major research areas that sex chromosomes are typically applied to, arguing that there are broad similarities not only between male-heterogametic (XX/XY) and female-heterogametic (ZZ/ZW) sex determination systems but also any mating system with reduced recombination in a sex-determining region. Further, general patterns of reduced diversity in nonrecombining regions are shared across plants and animals. There are unique patterns across populations with vastly different patterns of mating and speciation, but these do not tend to cluster by taxa or sex determination system.
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Affiliation(s)
- Melissa A Wilson Sayres
- School of Life Sciences, Center for Evolution and Medicine, The Biodesign Institute, Arizona State University
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25
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Hill T, Betancourt AJ. Extensive exchange of transposable elements in the Drosophila pseudoobscura group. Mob DNA 2018; 9:20. [PMID: 29946370 PMCID: PMC6006672 DOI: 10.1186/s13100-018-0123-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2018] [Accepted: 06/01/2018] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND As species diverge, so does their transposable element (TE) content. Within a genome, TE families may eventually become dormant due to host-silencing mechanisms, natural selection and the accumulation of inactive copies. The transmission of active copies from a TE families, both vertically and horizontally between species, can allow TEs to escape inactivation if it occurs often enough, as it may allow TEs to temporarily escape silencing in a new host. Thus, the contribution of horizontal exchange to TE persistence has been of increasing interest. RESULTS Here, we annotated TEs in five species with sequenced genomes from the D. pseudoobscura species group, and curated a set of TE families found in these species. We found that, compared to host genes, many TE families showed lower neutral divergence between species, consistent with recent transmission of TEs between species. Despite these transfers, there are differences in the TE content between species in the group. CONCLUSIONS The TE content is highly dynamic in the D. pseudoobscura species group, frequently transferring between species, keeping TEs active. This result highlights how frequently transposable elements are transmitted between sympatric species and, despite these transfers, how rapidly species TE content can diverge.
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Affiliation(s)
- Tom Hill
- The Department of Molecular Biosciences, University of Kansas, 4055 Haworth Hall, 1200 Sunnyside Avenue, Lawrence, KS 66045 USA
| | - Andrea J. Betancourt
- Institute of Integrative Biology, University of Liverpool, Liverpool, L69 7ZB UK
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26
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Dapper AL, Payseur BA. Connecting theory and data to understand recombination rate evolution. Philos Trans R Soc Lond B Biol Sci 2018; 372:rstb.2016.0469. [PMID: 29109228 DOI: 10.1098/rstb.2016.0469] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/07/2017] [Indexed: 02/03/2023] Open
Abstract
Meiotic recombination is necessary for successful gametogenesis in most sexually reproducing organisms and is a fundamental genomic parameter, influencing the efficacy of selection and the fate of new mutations. The molecular and evolutionary functions of recombination should impose strong selective constraints on the range of recombination rates. Yet, variation in recombination rate is observed on a variety of genomic and evolutionary scales. In the past decade, empirical studies have described variation in recombination rate within genomes, between individuals, between sexes, between populations and between species. At the same time, theoretical work has provided an increasingly detailed picture of the evolutionary advantages to recombination. Perhaps surprisingly, the causes of natural variation in recombination rate remain poorly understood. We argue that empirical and theoretical approaches to understand the evolution of recombination have proceeded largely independently of each other. Most models that address the evolution of recombination rate were created to explain the evolutionary advantage of recombination rather than quantitative differences in rate among individuals. Conversely, most empirical studies aim to describe variation in recombination rate, rather than to test evolutionary hypotheses. In this Perspective, we argue that efforts to integrate the rich bodies of empirical and theoretical work on recombination rate are crucial to moving this field forward. We provide new directions for the development of theory and the production of data that will jointly close this gap.This article is part of the themed issue 'Evolutionary causes and consequences of recombination rate variation in sexual organisms'.
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Affiliation(s)
- Amy L Dapper
- Laboratory of Genetics, University of Wisconsin, Madison, WI 53706, USA
| | - Bret A Payseur
- Laboratory of Genetics, University of Wisconsin, Madison, WI 53706, USA
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27
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Comeron JM. Background selection as null hypothesis in population genomics: insights and challenges from Drosophila studies. Philos Trans R Soc Lond B Biol Sci 2018; 372:rstb.2016.0471. [PMID: 29109230 PMCID: PMC5698629 DOI: 10.1098/rstb.2016.0471] [Citation(s) in RCA: 73] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/04/2017] [Indexed: 12/11/2022] Open
Abstract
The consequences of selection at linked sites are multiple and widespread across the genomes of most species. Here, I first review the main concepts behind models of selection and linkage in recombining genomes, present the difficulty in parametrizing these models simply as a reduction in effective population size (Ne) and discuss the predicted impact of recombination rates on levels of diversity across genomes. Arguments are then put forward in favour of using a model of selection and linkage with neutral and deleterious mutations (i.e. the background selection model, BGS) as a sensible null hypothesis for investigating the presence of other forms of selection, such as balancing or positive. I also describe and compare two studies that have generated high-resolution landscapes of the predicted consequences of selection at linked sites in Drosophila melanogaster. Both studies show that BGS can explain a very large fraction of the observed variation in diversity across the whole genome, thus supporting its use as null model. Finally, I identify and discuss a number of caveats and challenges in studies of genetic hitchhiking that have been often overlooked, with several of them sharing a potential bias towards overestimating the evidence supporting recent selective sweeps to the detriment of a BGS explanation. One potential source of bias is the analysis of non-equilibrium populations: it is precisely because models of selection and linkage predict variation in Ne across chromosomes that demographic dynamics are not expected to be equivalent chromosome- or genome-wide. Other challenges include the use of incomplete genome annotations, the assumption of temporally stable recombination landscapes, the presence of genes under balancing selection and the consequences of ignoring non-crossover (gene conversion) recombination events. This article is part of the themed issue ‘Evolutionary causes and consequences of recombination rate variation in sexual organisms’.
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Affiliation(s)
- Josep M Comeron
- Department of Biology, University of Iowa, Iowa City, IA 52242, USA .,Interdisciplinary Program in Genetics, University of Iowa, Iowa City, IA 52242, USA
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28
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RNA-Interference Pathways Display High Rates of Adaptive Protein Evolution in Multiple Invertebrates. Genetics 2018; 208:1585-1599. [PMID: 29437826 PMCID: PMC5887150 DOI: 10.1534/genetics.117.300567] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2017] [Accepted: 01/31/2018] [Indexed: 12/30/2022] Open
Abstract
Conflict between organisms can lead to a reciprocal adaptation that manifests as an increased evolutionary rate in genes mediating the conflict. This adaptive signature has been observed in RNA-interference (RNAi) pathway genes involved in the suppression of viruses and transposable elements in Drosophila melanogaster, suggesting that a subset of Drosophila RNAi genes may be locked in an arms race with these parasites. However, it is not known whether rapid evolution of RNAi genes is a general phenomenon across invertebrates, or which RNAi genes generally evolve adaptively. Here we use population genomic data from eight invertebrate species to infer rates of adaptive sequence evolution, and to test for past and ongoing selective sweeps in RNAi genes. We assess rates of adaptive protein evolution across species using a formal meta-analytic framework to combine data across species and by implementing a multispecies generalized linear mixed model of mutation counts. Across species, we find that RNAi genes display a greater rate of adaptive protein substitution than other genes, and that this is primarily mediated by positive selection acting on the genes most likely to defend against viruses and transposable elements. In contrast, evidence for recent selective sweeps is broadly spread across functional classes of RNAi genes and differs substantially among species. Finally, we identify genes that exhibit elevated adaptive evolution across the analyzed insect species, perhaps due to concurrent parasite-mediated arms races.
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Stevison LS, Sefick S, Rushton C, Graze RM. Recombination rate plasticity: revealing mechanisms by design. Philos Trans R Soc Lond B Biol Sci 2017; 372:20160459. [PMID: 29109222 PMCID: PMC5698621 DOI: 10.1098/rstb.2016.0459] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/01/2017] [Indexed: 12/13/2022] Open
Abstract
For over a century, scientists have known that meiotic recombination rates can vary considerably among individuals, and that environmental conditions can modify recombination rates relative to the background. A variety of external and intrinsic factors such as temperature, age, sex and starvation can elicit 'plastic' responses in recombination rate. The influence of recombination rate plasticity on genetic diversity of the next generation has interesting and important implications for how populations evolve. Further, many questions remain regarding the mechanisms and molecular processes that contribute to recombination rate plasticity. Here, we review 100 years of experimental work on recombination rate plasticity conducted in Drosophila melanogaster We categorize this work into four major classes of experimental designs, which we describe via classic studies in D. melanogaster Based on these studies, we highlight molecular mechanisms that are supported by experimental results and relate these findings to studies in other systems. We synthesize lessons learned from this model system into experimental guidelines for using recent advances in genotyping technologies, to study recombination rate plasticity in non-model organisms. Specifically, we recommend (1) using fine-scale genome-wide markers, (2) collecting time-course data, (3) including crossover distribution measurements, and (4) using mixed effects models to analyse results. To illustrate this approach, we present an application adhering to these guidelines from empirical work we conducted in Drosophila pseudoobscuraThis article is part of the themed issue 'Evolutionary causes and consequences of recombination rate variation in sexual organisms'.
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Affiliation(s)
- Laurie S Stevison
- Department of Biological Sciences, Auburn University, Auburn, AL 36849, USA
| | - Stephen Sefick
- Department of Biological Sciences, Auburn University, Auburn, AL 36849, USA
| | - Chase Rushton
- Department of Biological Sciences, Auburn University, Auburn, AL 36849, USA
| | - Rita M Graze
- Department of Biological Sciences, Auburn University, Auburn, AL 36849, USA
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30
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Mohammed J, Flynt AS, Panzarino AM, Mondal MMH, DeCruz M, Siepel A, Lai EC. Deep experimental profiling of microRNA diversity, deployment, and evolution across the Drosophila genus. Genome Res 2017; 28:52-65. [PMID: 29233922 PMCID: PMC5749182 DOI: 10.1101/gr.226068.117] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Accepted: 11/20/2017] [Indexed: 11/24/2022]
Abstract
To assess miRNA evolution across the Drosophila genus, we analyzed several billion small RNA reads across 12 fruit fly species. These data permit comprehensive curation of species- and clade-specific variation in miRNA identity, abundance, and processing. Among well-conserved miRNAs, we observed unexpected cases of clade-specific variation in 5' end precision, occasional antisense loci, and putatively noncanonical loci. We also used strict criteria to identify a large set (649) of novel, evolutionarily restricted miRNAs. Within the bulk collection of species-restricted miRNAs, two notable subpopulations are splicing-derived mirtrons and testes-restricted, recently evolved, clustered (TRC) canonical miRNAs. We quantified miRNA birth and death using our annotation and a phylogenetic model for estimating rates of miRNA turnover. We observed striking differences in birth and death rates across miRNA classes defined by biogenesis pathway, genomic clustering, and tissue restriction, and even identified flux heterogeneity among Drosophila clades. In particular, distinct molecular rationales underlie the distinct evolutionary behavior of different miRNA classes. Mirtrons are associated with high rates of 3' untemplated addition, a mechanism that impedes their biogenesis, whereas TRC miRNAs appear to evolve under positive selection. Altogether, these data reveal miRNA diversity among Drosophila species and principles underlying their emergence and evolution.
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Affiliation(s)
- Jaaved Mohammed
- Department of Biological Statistics and Computational Biology, Cornell University, Ithaca, New York 14853, USA.,Tri-Institutional Training Program in Computational Biology and Medicine, New York, New York 10021, USA.,Department of Developmental Biology, Sloan-Kettering Institute, New York, New York 10065, USA.,Simons Center for Quantitative Biology, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA
| | - Alex S Flynt
- Department of Developmental Biology, Sloan-Kettering Institute, New York, New York 10065, USA.,Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, Mississippi 39406, USA
| | - Alexandra M Panzarino
- Department of Developmental Biology, Sloan-Kettering Institute, New York, New York 10065, USA
| | | | - Matthew DeCruz
- Department of Biological Sciences, University of Southern Mississippi, Hattiesburg, Mississippi 39406, USA
| | - Adam Siepel
- Simons Center for Quantitative Biology, Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA
| | - Eric C Lai
- Tri-Institutional Training Program in Computational Biology and Medicine, New York, New York 10021, USA.,Department of Developmental Biology, Sloan-Kettering Institute, New York, New York 10065, USA
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31
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Fuller ZL, Haynes GD, Richards S, Schaeffer SW. Genomics of natural populations: Evolutionary forces that establish and maintain gene arrangements inDrosophila pseudoobscura. Mol Ecol 2017; 26:6539-6562. [DOI: 10.1111/mec.14381] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2017] [Revised: 10/04/2017] [Accepted: 10/07/2017] [Indexed: 12/19/2022]
Affiliation(s)
- Zachary L. Fuller
- Department of Biology; 208 Erwin W. Mueller Laboratory; The Pennsylvania State University; University Park PA USA
| | - Gwilym D. Haynes
- Department of Biology; 208 Erwin W. Mueller Laboratory; The Pennsylvania State University; University Park PA USA
| | - Stephen Richards
- Human Genome Sequencing Center; Baylor College of Medicine; Houston TX USA
| | - Stephen W. Schaeffer
- Department of Biology; 208 Erwin W. Mueller Laboratory; The Pennsylvania State University; University Park PA USA
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32
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Kamdem C, Fouet C, White BJ. Chromosome arm-specific patterns of polymorphism associated with chromosomal inversions in the major African malaria vector, Anopheles funestus. Mol Ecol 2017; 26:5552-5566. [PMID: 28833796 PMCID: PMC5927613 DOI: 10.1111/mec.14335] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2016] [Revised: 08/08/2017] [Accepted: 08/14/2017] [Indexed: 02/02/2023]
Abstract
Chromosomal inversions facilitate local adaptation of beneficial mutations and modulate genetic polymorphism, but the extent of their effects within the genome is still insufficiently understood. The genome of Anopheles funestus, a malaria mosquito endemic to sub-Saharan Africa, contains an impressive number of paracentric polymorphic inversions, which are unevenly distributed among chromosomes and provide an excellent framework for investigating the genomic impacts of chromosomal rearrangements. Here, we present results of a fine-scale analysis of genetic variation within the genome of two weakly differentiated populations of Anopheles funestus inhabiting contrasting moisture conditions in Cameroon. Using population genomic analyses, we found that genetic divergence between the two populations is centred on regions of the genome corresponding to three inversions, which are characterized by high values of FST , absolute sequence divergence and fixed differences. Importantly, in contrast to the 2L chromosome arm, which is collinear, nucleotide diversity is significantly reduced along the entire length of three autosome arms bearing multiple overlapping chromosomal rearrangements. These findings support the idea that interactions between reduced recombination and natural selection within inversions contribute to sculpt nucleotide polymorphism across chromosomes in An. funestus.
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Affiliation(s)
- Colince Kamdem
- Department of Entomology, University of California, Riverside, CA 92521
| | - Caroline Fouet
- Department of Entomology, University of California, Riverside, CA 92521
| | - Bradley J. White
- Department of Entomology, University of California, Riverside, CA 92521
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33
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Ortiz‐Barrientos D, James ME. Evolution of recombination rates and the genomic landscape of speciation. J Evol Biol 2017; 30:1519-1521. [DOI: 10.1111/jeb.13116] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2017] [Revised: 05/07/2017] [Accepted: 05/08/2017] [Indexed: 01/02/2023]
Affiliation(s)
- D. Ortiz‐Barrientos
- School of Biological Sciences The University of Queensland St Lucia Qld Australia
| | - M. E. James
- School of Biological Sciences The University of Queensland St Lucia Qld Australia
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34
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Variation in Recombination Rate: Adaptive or Not? Trends Genet 2017; 33:364-374. [DOI: 10.1016/j.tig.2017.03.003] [Citation(s) in RCA: 100] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Revised: 03/06/2017] [Accepted: 03/07/2017] [Indexed: 01/30/2023]
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35
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Modliszewski JL, Copenhaver GP. Meiotic recombination gets stressed out: CO frequency is plastic under pressure. CURRENT OPINION IN PLANT BIOLOGY 2017; 36:95-102. [PMID: 28258986 DOI: 10.1016/j.pbi.2016.11.019] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Accepted: 11/13/2016] [Indexed: 05/02/2023]
Abstract
Meiotic recombination ensures the fertility of gametes and creates novel genetic combinations. Although meiotic crossover (CO) frequency is under homeostatic control, CO frequency is also plastic in nature and can respond to environmental conditions. Most investigations have focused on temperature and recombination, but other external and internal stimuli also have important roles in modulating CO frequency. Even less is understood about the molecular mechanisms that underly these phenomenon, but recent work has begun to advance our knowledge in this field. In this review, we identify and explore potential mechanisms including changes in: the synaptonemal complex, chromatin state, DNA methylation, and RNA splicing.
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Affiliation(s)
- Jennifer L Modliszewski
- Department of Biology and the Integrative Program for Biological and Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, United States.
| | - Gregory P Copenhaver
- Department of Biology and the Integrative Program for Biological and Genome Sciences, University of North Carolina at Chapel Hill, Chapel Hill, United States; Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, Chapel Hill, United States
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36
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Liu H, Jia Y, Sun X, Tian D, Hurst LD, Yang S. Direct Determination of the Mutation Rate in the Bumblebee Reveals Evidence for Weak Recombination-Associated Mutation and an Approximate Rate Constancy in Insects. Mol Biol Evol 2017; 34:119-130. [PMID: 28007973 PMCID: PMC5854123 DOI: 10.1093/molbev/msw226] [Citation(s) in RCA: 64] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Accurate knowledge of the mutation rate provides a base line for inferring expected rates of evolution, for testing evolutionary hypotheses and for estimation of key parameters. Advances in sequencing technology now permit direct estimates of the mutation rate from sequencing of close relatives. Within insects there have been three prior such estimates, two in nonsocial insects (Drosophila: 2.8 × 10-9 per bp per haploid genome per generation; Heliconius: 2.9 × 10-9) and one in a social species, the honeybee (3.4 × 10-9). Might the honeybee's rate be ∼20% higher because it has an exceptionally high recombination rate and recombination may be directly or indirectly mutagenic? To address this possibility, we provide a direct estimate of the mutation rate in the bumblebee (Bombus terrestris), this being a close relative of the honeybee but with a much lower recombination rate. We confirm that the crossover rate of the bumblebee is indeed much lower than honeybees (8.7 cM/Mb vs. 37 cM/Mb). Importantly, we find no significant difference in the mutation rates: we estimate for bumblebees a rate of 3.6 × 10-9 per haploid genome per generation (95% confidence intervals 2.38 × 10-9 and 5.37 × 10-9) which is just 5% higher than the estimate that of honeybees. Both genomes have approximately one new mutation per haploid genome per generation. While we find evidence for a direct coupling between recombination and mutation (also seen in honeybees), the effect is so weak as to leave almost no footprint on any between-species differences. The similarity in mutation rates suggests an approximate constancy of the mutation rate in insects.
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Affiliation(s)
- Haoxuan Liu
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, China
| | - Yanxiao Jia
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, China
| | - Xiaoguang Sun
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, China
| | - Dacheng Tian
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, China
| | - Laurence D Hurst
- Department of Biology and Biochemistry, The Milner Centre for Evolution, University of Bath, Bath, United Kingdom
| | - Sihai Yang
- State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, China
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37
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Ritz KR, Noor MAF. Mistaken Identity: Another Bias in the Use of Relative Genetic Divergence Measures for Detecting Interspecies Introgression. PLoS One 2016; 11:e0165032. [PMID: 27760228 PMCID: PMC5070774 DOI: 10.1371/journal.pone.0165032] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Accepted: 10/05/2016] [Indexed: 11/18/2022] Open
Abstract
Measures of genetic divergence have long been used to identify evolutionary processes operating within and between species. However, recent reviews have described a bias in the use of relative divergence measures towards incorrectly identifying genomic regions that are seemingly immune to introgression. Here, we present a novel and opposite bias of relative divergence measures: misidentifying regions of introgression between sister species. We examine two distinct haplotypes of intermediate frequency within Drosophila pseudoobscura at the DPSX009 locus. One of these haplotypes had lower relative divergence than another to sister species D. persimilis. Although we and others initially presumed one haplotype have spread via introgression between D. pseudoobscura and D. persimilis, absolute divergence measures and individual sequence analysis suggest that haplotype structuring occurred as the result of within-species processes. The potential for this type of misinference may occur with any haplotype that recently spread within a species. We conclude that absolute measures of genetic divergence are necessary for confirming putative regions of introgression.
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Affiliation(s)
- Kathryn R. Ritz
- Department of Biology, Duke University, Durham, North Carolina, United States of America
- * E-mail:
| | - Mohamed A. F. Noor
- Department of Biology, Duke University, Durham, North Carolina, United States of America
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38
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Lewis SH, Webster CL, Salmela H, Obbard DJ. Repeated Duplication of Argonaute2 Is Associated with Strong Selection and Testis Specialization in Drosophila. Genetics 2016; 204:757-769. [PMID: 27535930 PMCID: PMC5068860 DOI: 10.1534/genetics.116.192336] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2016] [Accepted: 08/12/2016] [Indexed: 11/18/2022] Open
Abstract
Argonaute2 (Ago2) is a rapidly evolving nuclease in the Drosophila melanogaster RNA interference (RNAi) pathway that targets viruses and transposable elements in somatic tissues. Here we reconstruct the history of Ago2 duplications across the D. obscura group and use patterns of gene expression to infer new functional specialization. We show that some duplications are old, shared by the entire species group, and that losses may be common, including previously undetected losses in the lineage leading to D. pseudoobscura We find that while the original (syntenic) gene copy has generally retained the ancestral ubiquitous expression pattern, most of the novel Ago2 paralogs have independently specialized to testis-specific expression. Using population genetic analyses, we show that most testis-specific paralogs have significantly lower genetic diversity than the genome-wide average. This suggests recent positive selection in three different species, and model-based analyses provide strong evidence of recent hard selective sweeps in or near four of the six D. pseudoobscura Ago2 paralogs. We speculate that the repeated evolution of testis specificity in obscura group Ago2 genes, combined with their dynamic turnover and strong signatures of adaptive evolution, may be associated with highly derived roles in the suppression of transposable elements or meiotic drive. Our study highlights the lability of RNAi pathways, even within well-studied groups such as Drosophila, and suggests that strong selection may act quickly after duplication in RNAi pathways, potentially giving rise to new and unknown RNAi functions in nonmodel species.
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Affiliation(s)
- Samuel H Lewis
- Institute of Evolutionary Biology, University of Edinburgh, Ashworth Laboratories, EH9 3FL, United Kingdom
| | - Claire L Webster
- Institute of Evolutionary Biology, University of Edinburgh, Ashworth Laboratories, EH9 3FL, United Kingdom
| | - Heli Salmela
- Department of Biosciences, Centre of Excellence in Biological Interactions, University of Helsinki, Finland
| | - Darren J Obbard
- Institute of Evolutionary Biology, University of Edinburgh, Ashworth Laboratories, EH9 3FL, United Kingdom Centre for Immunity, Infection and Evolution, University of Edinburgh, Ashworth Laboratories, EH9 3FL, United Kingdom
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39
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Adrian AB, Corchado JC, Comeron JM. Predictive Models of Recombination Rate Variation across the Drosophila melanogaster Genome. Genome Biol Evol 2016; 8:2597-612. [PMID: 27492232 PMCID: PMC5010912 DOI: 10.1093/gbe/evw181] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
In all eukaryotic species examined, meiotic recombination, and crossovers in particular, occur non‐randomly along chromosomes. The cause for this non-random distribution remains poorly understood but some specific DNA sequence motifs have been shown to be enriched near crossover hotspots in a number of species. We present analyses using machine learning algorithms to investigate whether DNA motif distribution across the genome can be used to predict crossover variation in Drosophila melanogaster, a species without hotspots. Our study exposes a combinatorial non-linear influence of motif presence able to account for a significant fraction of the genome-wide variation in crossover rates at all genomic scales investigated, from 20% at 5-kb to almost 70% at 2,500-kb scale. The models are particularly predictive for regions with the highest and lowest crossover rates and remain highly informative after removing sub-telomeric and -centromeric regions known to have strongly reduced crossover rates. Transcriptional activity during early meiosis and differences in motif use between autosomes and the X chromosome add to the predictive power of the models. Moreover, we show that population-specific differences in crossover rates can be partly explained by differences in motif presence. Our results suggest that crossover distribution in Drosophila is influenced by both meiosis-specific chromatin dynamics and very local constitutive open chromatin associated with DNA motifs that prevent nucleosome stabilization. These findings provide new information on the genetic factors influencing variation in recombination rates and a baseline to study epigenetic mechanisms responsible for plastic recombination as response to different biotic and abiotic conditions and stresses.
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Affiliation(s)
| | | | - Josep M Comeron
- Department of Biology, University of Iowa Interdisciplinary Graduate Program in Genetics, University of Iowa
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40
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Xue C, Chen H, Yu F. Base-Biased Evolution of Disease-Associated Mutations in the Human Genome. Hum Mutat 2016; 37:1209-1214. [PMID: 27507420 DOI: 10.1002/humu.23065] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2016] [Revised: 08/02/2016] [Accepted: 08/07/2016] [Indexed: 11/08/2022]
Abstract
Understanding the evolution of disease-associated mutations is fundamental to analyze pathogenetics of diseases. Mutation, recombination (by GC-biased gene conversion, gBGC), and selection have been known to shape the evolution of disease-associated mutations, but how these evolutionary forces work together is still an open question. In this study, we analyzed several human large-scale datasets (1000 Genomes, ESP6500, ExAC and ClinVar), and found that base-biased mutagenesis generates more GC→AT than AT→GC mutations, while gBGC promotes the fixation of AT→GC mutations to balance the impact of base-biased mutation on genome. Due to this effect of gBGC, purifying selection removes more deleterious AT→GC mutations than GC→AT from population, but many high-frequency (fixed and nearly fixed) deleterious AT→GC mutations are remained possibly due to high genetic load. As a special subset, disease-associated mutations follow this evolutionary rule, in which disease-associated GC→AT mutations are more enriched in rare mutations compared with AT→GC, while disease-associated AT→GC are more enriched in mutations with high frequency. Thus, we presented a base-biased evolutionary framework that explains the base-biased generation and accumulation of disease-associated mutations in human populations.
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Affiliation(s)
- Cheng Xue
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas
| | - Hua Chen
- Center for Computational Genomics, Beijing Institute of Genomics, Chinese Academy of Sciences, Beijing, China
| | - Fuli Yu
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, Texas.
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41
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Gante HF, Matschiner M, Malmstrøm M, Jakobsen KS, Jentoft S, Salzburger W. Genomics of speciation and introgression in Princess cichlid fishes from Lake Tanganyika. Mol Ecol 2016; 25:6143-6161. [DOI: 10.1111/mec.13767] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Revised: 05/30/2016] [Accepted: 07/11/2016] [Indexed: 01/02/2023]
Affiliation(s)
- Hugo F. Gante
- Zoological Institute University of Basel Vesalgasse 1 4051 Basel Switzerland
| | - Michael Matschiner
- Department of Biosciences CEES (Centre for Ecological and Evolutionary Synthesis) University of Oslo 0316 Oslo Norway
| | - Martin Malmstrøm
- Department of Biosciences CEES (Centre for Ecological and Evolutionary Synthesis) University of Oslo 0316 Oslo Norway
| | - Kjetill S. Jakobsen
- Department of Biosciences CEES (Centre for Ecological and Evolutionary Synthesis) University of Oslo 0316 Oslo Norway
| | - Sissel Jentoft
- Department of Biosciences CEES (Centre for Ecological and Evolutionary Synthesis) University of Oslo 0316 Oslo Norway
- Department of Natural Sciences University of Agder 4604 Kristiansand Norway
| | - Walter Salzburger
- Zoological Institute University of Basel Vesalgasse 1 4051 Basel Switzerland
- Department of Biosciences CEES (Centre for Ecological and Evolutionary Synthesis) University of Oslo 0316 Oslo Norway
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42
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Abstract
Fruit flies of the genus Drosophila have been an attractive and effective genetic model organism since Thomas Hunt Morgan and colleagues made seminal discoveries with them a century ago. Work with Drosophila has enabled dramatic advances in cell and developmental biology, neurobiology and behavior, molecular biology, evolutionary and population genetics, and other fields. With more tissue types and observable behaviors than in other short-generation model organisms, and with vast genome data available for many species within the genus, the fly's tractable complexity will continue to enable exciting opportunities to explore mechanisms of complex developmental programs, behaviors, and broader evolutionary questions. This primer describes the organism's natural history, the features of sequenced genomes within the genus, the wide range of available genetic tools and online resources, the types of biological questions Drosophila can help address, and historical milestones.
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43
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Phung TN, Huber CD, Lohmueller KE. Determining the Effect of Natural Selection on Linked Neutral Divergence across Species. PLoS Genet 2016; 12:e1006199. [PMID: 27508305 PMCID: PMC4980041 DOI: 10.1371/journal.pgen.1006199] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Accepted: 06/25/2016] [Indexed: 11/18/2022] Open
Abstract
A major goal in evolutionary biology is to understand how natural selection has shaped patterns of genetic variation across genomes. Studies in a variety of species have shown that neutral genetic diversity (intra-species differences) has been reduced at sites linked to those under direct selection. However, the effect of linked selection on neutral sequence divergence (inter-species differences) remains ambiguous. While empirical studies have reported correlations between divergence and recombination, which is interpreted as evidence for natural selection reducing linked neutral divergence, theory argues otherwise, especially for species that have diverged long ago. Here we address these outstanding issues by examining whether natural selection can affect divergence between both closely and distantly related species. We show that neutral divergence between closely related species (e.g. human-primate) is negatively correlated with functional content and positively correlated with human recombination rate. We also find that neutral divergence between distantly related species (e.g. human-rodent) is negatively correlated with functional content and positively correlated with estimates of background selection from primates. These patterns persist after accounting for the confounding factors of hypermutable CpG sites, GC content, and biased gene conversion. Coalescent models indicate that even when the contribution of ancestral polymorphism to divergence is small, background selection in the ancestral population can still explain a large proportion of the variance in divergence across the genome, generating the observed correlations. Our findings reveal that, contrary to previous intuition, natural selection can indirectly affect linked neutral divergence between both closely and distantly related species. Though we cannot formally exclude the possibility that the direct effects of purifying selection drive some of these patterns, such a scenario would be possible only if more of the genome is under purifying selection than currently believed. Our work has implications for understanding the evolution of genomes and interpreting patterns of genetic variation. Genetic variation at neutral sites can be reduced through linkage to nearby selected sites. This pattern has been used to show the widespread effects of natural selection at shaping patterns of genetic diversity across genomes from a variety of species. However, it is not entirely clear whether natural selection has an effect on neutral divergence between species. Here we show that putatively neutral divergence between closely related species (human and chimp) and between distantly related pairs of species (humans and mice) show signatures consistent with having been affected by linkage to selected sites. Further, our theoretical models and simulations show that natural selection indirectly affecting linked neutral sites can generate these patterns. Unless substantially more of the genome is under the direct effects of purifying selection than currently believed, our results argue that natural selection has played an important role in shaping variation in levels of putatively neutral sequence divergence across the genome. Our findings further suggest that divergence-based estimates of neutral mutation rate variation across the genome as well as certain estimators of population history may be confounded by linkage to selected sites.
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Affiliation(s)
- Tanya N. Phung
- Interdepartmental Program in Bioinformatics, University of California, Los Angeles, Los Angeles, California, United States of America
| | - Christian D. Huber
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, California, United States of America
| | - Kirk E. Lohmueller
- Interdepartmental Program in Bioinformatics, University of California, Los Angeles, Los Angeles, California, United States of America
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, Los Angeles, California, United States of America
- Department of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, United States of America
- * E-mail:
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44
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Korunes KL, Noor MAF. Gene conversion and linkage: effects on genome evolution and speciation. Mol Ecol 2016; 26:351-364. [DOI: 10.1111/mec.13736] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Revised: 06/07/2016] [Accepted: 06/22/2016] [Indexed: 12/12/2022]
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Kenney AM, Sweigart AL. Reproductive isolation and introgression between sympatric
Mimulus
species. Mol Ecol 2016; 25:2499-517. [DOI: 10.1111/mec.13630] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Revised: 03/18/2016] [Accepted: 03/22/2016] [Indexed: 01/19/2023]
Affiliation(s)
- Amanda M. Kenney
- Department of Genetics University of Georgia Athens GA 30602 USA
- Department of Biological Sciences St. Edward's University Austin TX 78704 USA
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Smeds L, Mugal CF, Qvarnström A, Ellegren H. High-Resolution Mapping of Crossover and Non-crossover Recombination Events by Whole-Genome Re-sequencing of an Avian Pedigree. PLoS Genet 2016; 12:e1006044. [PMID: 27219623 PMCID: PMC4878770 DOI: 10.1371/journal.pgen.1006044] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Accepted: 04/19/2016] [Indexed: 01/04/2023] Open
Abstract
Recombination is an engine of genetic diversity and therefore constitutes a key process in evolutionary biology and genetics. While the outcome of crossover recombination can readily be detected as shuffled alleles by following the inheritance of markers in pedigreed families, the more precise location of both crossover and non-crossover recombination events has been difficult to pinpoint. As a consequence, we lack a detailed portrait of the recombination landscape for most organisms and knowledge on how this landscape impacts on sequence evolution at a local scale. To localize recombination events with high resolution in an avian system, we performed whole-genome re-sequencing at high coverage of a complete three-generation collared flycatcher pedigree. We identified 325 crossovers at a median resolution of 1.4 kb, with 86% of the events localized to <10 kb intervals. Observed crossover rates were in excellent agreement with data from linkage mapping, were 52% higher in male (3.56 cM/Mb) than in female meiosis (2.28 cM/Mb), and increased towards chromosome ends in male but not female meiosis. Crossover events were non-randomly distributed in the genome with several distinct hot-spots and a concentration to genic regions, with the highest density in promoters and CpG islands. We further identified 267 non-crossovers, whose location was significantly associated with crossover locations. We detected a significant transmission bias (0.18) in favour of 'strong' (G, C) over 'weak' (A, T) alleles at non-crossover events, providing direct evidence for the process of GC-biased gene conversion in an avian system. The approach taken in this study should be applicable to any species and would thereby help to provide a more comprehensive portray of the recombination landscape across organism groups.
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Affiliation(s)
- Linnéa Smeds
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden
| | - Carina F. Mugal
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden
| | - Anna Qvarnström
- Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden
| | - Hans Ellegren
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden
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Stevison LS, Woerner AE, Kidd JM, Kelley JL, Veeramah KR, McManus KF, Bustamante CD, Hammer MF, Wall JD. The Time Scale of Recombination Rate Evolution in Great Apes. Mol Biol Evol 2016; 33:928-45. [PMID: 26671457 PMCID: PMC5870646 DOI: 10.1093/molbev/msv331] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
We present three linkage-disequilibrium (LD)-based recombination maps generated using whole-genome sequence data from 10 Nigerian chimpanzees, 13 bonobos, and 15 western gorillas, collected as part of the Great Ape Genome Project (Prado-Martinez J, et al. 2013. Great ape genetic diversity and population history. Nature 499:471-475). We also identified species-specific recombination hotspots in each group using a modified LDhot framework, which greatly improves statistical power to detect hotspots at varying strengths. We show that fewer hotspots are shared among chimpanzee subspecies than within human populations, further narrowing the time scale of complete hotspot turnover. Further, using species-specific PRDM9 sequences to predict potential binding sites (PBS), we show higher predicted PRDM9 binding in recombination hotspots as compared to matched cold spot regions in multiple great ape species, including at least one chimpanzee subspecies. We found that correlations between broad-scale recombination rates decline more rapidly than nucleotide divergence between species. We also compared the skew of recombination rates at centromeres and telomeres between species and show a skew from chromosome means extending as far as 10-15 Mb from chromosome ends. Further, we examined broad-scale recombination rate changes near a translocation in gorillas and found minimal differences as compared to other great ape species perhaps because the coordinates relative to the chromosome ends were unaffected. Finally, on the basis of multiple linear regression analysis, we found that various correlates of recombination rate persist throughout the African great apes including repeats, diversity, and divergence. Our study is the first to analyze within- and between-species genome-wide recombination rate variation in several close relatives.
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Affiliation(s)
- Laurie S Stevison
- Institute for Human Genetics, University of California San Francisco Department of Biological Sciences, Auburn University
| | - August E Woerner
- Arizona Research Laboratories, Division of Biotechnology, University of Arizona Department of Genetics, University of Arizona
| | - Jeffrey M Kidd
- Department of Human Genetics, University of Michigan Department of Computational Medicine & Bioinformatics, University of Michigan
| | - Joanna L Kelley
- School of Biological Sciences, Washington State University Department of Genetics, Stanford University
| | - Krishna R Veeramah
- Arizona Research Laboratories, Division of Biotechnology, University of Arizona Department of Ecology and Evolution, Stony Brook University
| | - Kimberly F McManus
- Department of Biology, Stanford University Department of Biomedical Informatics, Stanford University
| | | | - Michael F Hammer
- Arizona Research Laboratories, Division of Biotechnology, University of Arizona Department of Ecology and Evolutionary Biology, University of Arizona Department of Anthropology, University of Arizona
| | - Jeffrey D Wall
- Institute for Human Genetics, University of California San Francisco Department of Epidemiology & Biostatistics, University of California San Francisco
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48
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Natural Selection and Genetic Diversity in the Butterfly Heliconius melpomene. Genetics 2016; 203:525-41. [PMID: 27017626 PMCID: PMC4858797 DOI: 10.1534/genetics.115.183285] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Accepted: 03/21/2016] [Indexed: 11/18/2022] Open
Abstract
A combination of selective and neutral evolutionary forces shape patterns of genetic diversity in nature. Among the insects, most previous analyses of the roles of drift and selection in shaping variation across the genome have focused on the genus Drosophila A more complete understanding of these forces will come from analyzing other taxa that differ in population demography and other aspects of biology. We have analyzed diversity and signatures of selection in the neotropical Heliconius butterflies using resequenced genomes from 58 wild-caught individuals of Heliconius melpomene and another 21 resequenced genomes representing 11 related species. By comparing intraspecific diversity and interspecific divergence, we estimate that 31% of amino acid substitutions between Heliconius species are adaptive. Diversity at putatively neutral sites is negatively correlated with the local density of coding sites as well as nonsynonymous substitutions and positively correlated with recombination rate, indicating widespread linked selection. This process also manifests in significantly reduced diversity on longer chromosomes, consistent with lower recombination rates. Although hitchhiking around beneficial nonsynonymous mutations has significantly shaped genetic variation in H. melpomene, evidence for strong selective sweeps is limited overall. We did however identify two regions where distinct haplotypes have swept in different populations, leading to increased population differentiation. On the whole, our study suggests that positive selection is less pervasive in these butterflies as compared to fruit flies, a fact that curiously results in very similar levels of neutral diversity in these very different insects.
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49
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Natural Selection and Recombination Rate Variation Shape Nucleotide Polymorphism Across the Genomes of Three Related Populus Species. Genetics 2015; 202:1185-200. [PMID: 26721855 PMCID: PMC4788117 DOI: 10.1534/genetics.115.183152] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Accepted: 12/24/2015] [Indexed: 12/30/2022] Open
Abstract
A central aim of evolutionary genomics is to identify the relative roles that various evolutionary forces have played in generating and shaping genetic variation within and among species. Here we use whole-genome resequencing data to characterize and compare genome-wide patterns of nucleotide polymorphism, site frequency spectrum, and population-scaled recombination rates in three species of Populus: Populus tremula, P. tremuloides, and P. trichocarpa. We find that P. tremuloides has the highest level of genome-wide variation, skewed allele frequencies, and population-scaled recombination rates, whereas P. trichocarpa harbors the lowest. Our findings highlight multiple lines of evidence suggesting that natural selection, due to both purifying and positive selection, has widely shaped patterns of nucleotide polymorphism at linked neutral sites in all three species. Differences in effective population sizes and rates of recombination largely explain the disparate magnitudes and signatures of linked selection that we observe among species. The present work provides the first phylogenetic comparative study on a genome-wide scale in forest trees. This information will also improve our ability to understand how various evolutionary forces have interacted to influence genome evolution among related species.
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50
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Aggarwal DD, Rashkovetsky E, Michalak P, Cohen I, Ronin Y, Zhou D, Haddad GG, Korol AB. Experimental evolution of recombination and crossover interference in Drosophila caused by directional selection for stress-related traits. BMC Biol 2015; 13:101. [PMID: 26614097 PMCID: PMC4661966 DOI: 10.1186/s12915-015-0206-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2015] [Accepted: 10/27/2015] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND Population genetics predicts that tight linkage between new and/or pre-existing beneficial and deleterious alleles should decrease the efficiency of natural selection in finite populations. By decoupling beneficial and deleterious alleles and facilitating the combination of beneficial alleles, recombination accelerates the formation of high-fitness genotypes. This may impose indirect selection for increased recombination. Despite the progress in theoretical understanding, interplay between recombination and selection remains a controversial issue in evolutionary biology. Even less satisfactory is the situation with crossover interference, which is a deviation of double-crossover frequency in a pair of adjacent intervals from the product of recombination rates in the two intervals expected on the assumption of crossover independence. Here, we report substantial changes in recombination and interference in three long-term directional selection experiments with Drosophila melanogaster: for desiccation (~50 generations), hypoxia, and hyperoxia tolerance (>200 generations each). RESULTS For all three experiments, we found a high interval-specific increase of recombination frequencies in selection lines (up to 40-50% per interval) compared to the control lines. We also discovered a profound effect of selection on interference as expressed by an increased frequency of double crossovers in selection lines. Our results show that changes in interference are not necessarily coupled with increased recombination. CONCLUSIONS Our results support the theoretical predictions that adaptation to a new environment can promote evolution toward higher recombination. Moreover, this is the first evidence of selection for different recombination-unrelated traits potentially leading, not only to evolution toward increased crossover rates, but also to changes in crossover interference, one of the fundamental features of recombination.
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Affiliation(s)
| | | | - Pawel Michalak
- Virginia Bioinformatics Institute, Virginia Tech, Washington Street, MC 0477, Blacksburg, VA, 24061-0477, USA
| | - Irit Cohen
- Institute of Evolution, University of Haifa, Haifa, 3498838, Israel
| | - Yefim Ronin
- Institute of Evolution, University of Haifa, Haifa, 3498838, Israel
| | - Dan Zhou
- University of California, San Diego, USA
| | - Gabriel G Haddad
- University of California, San Diego, USA
- Rady Children's Hospital, San Diego, USA
| | - Abraham B Korol
- Institute of Evolution, University of Haifa, Haifa, 3498838, Israel.
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