1
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Feng S, DeGrey SP, Guédot C, Schoville SD, Pool JE. Genomic Diversity Illuminates the Environmental Adaptation of Drosophila suzukii. Genome Biol Evol 2024; 16:evae195. [PMID: 39235033 PMCID: PMC11421661 DOI: 10.1093/gbe/evae195] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2024] [Revised: 07/09/2024] [Accepted: 08/21/2024] [Indexed: 09/06/2024] Open
Abstract
Biological invasions carry substantial practical and scientific importance and represent natural evolutionary experiments on contemporary timescales. Here, we investigated genomic diversity and environmental adaptation of the crop pest Drosophila suzukii using whole-genome sequencing data and environmental metadata for 29 population samples from its native and invasive range. Through a multifaceted analysis of this population genomic data, we increase our understanding of the D. suzukii genome, its diversity and its evolution, and we identify an appropriate genotype-environment association pipeline for our dataset. Using this approach, we detect genetic signals of local adaptation associated with nine distinct environmental factors related to altitude, wind speed, precipitation, temperature, and human land use. We uncover unique functional signatures for each environmental variable, such as the prevalence of cuticular genes associated with annual precipitation. We also infer biological commonalities in the adaptation to diverse selective pressures, particularly in terms of the apparent contribution of nervous system evolution to enriched processes (ranging from neuron development to circadian behavior) and to top genes associated with all nine environmental variables. Our findings therefore depict a finer-scale adaptive landscape underlying the rapid invasion success of this agronomically important species.
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Affiliation(s)
- Siyuan Feng
- Laboratory of Genetics, University of Wisconsin–Madison, Madison, WI, USA
| | - Samuel P DeGrey
- Department of Entomology, University of Wisconsin-Madison, Madison, WI, USA
| | - Christelle Guédot
- Department of Entomology, University of Wisconsin-Madison, Madison, WI, USA
| | - Sean D Schoville
- Department of Entomology, University of Wisconsin-Madison, Madison, WI, USA
| | - John E Pool
- Laboratory of Genetics, University of Wisconsin–Madison, Madison, WI, USA
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2
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Shogren EH, Sardell JM, Muirhead CA, Martí E, Cooper EA, Moyle RG, Presgraves DC, Uy JAC. Recent secondary contact, genome-wide admixture, and asymmetric introgression of neo-sex chromosomes between two Pacific island bird species. PLoS Genet 2024; 20:e1011360. [PMID: 39172766 PMCID: PMC11340901 DOI: 10.1371/journal.pgen.1011360] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2023] [Accepted: 06/28/2024] [Indexed: 08/24/2024] Open
Abstract
Secondary contact between closely related taxa represents a "moment of truth" for speciation-an opportunity to test the efficacy of reproductive isolation that evolved in allopatry and to identify the genetic, behavioral, and/or ecological barriers that separate species in sympatry. Sex chromosomes are known to rapidly accumulate differences between species, an effect that may be exacerbated for neo-sex chromosomes that are transitioning from autosomal to sex-specific inheritance. Here we report that, in the Solomon Islands, two closely related bird species in the honeyeater family-Myzomela cardinalis and Myzomela tristrami-carry neo-sex chromosomes and have come into recent secondary contact after ~1.1 my of geographic isolation. Hybrids of the two species were first observed in sympatry ~100 years ago. To determine the genetic consequences of hybridization, we use population genomic analyses of individuals sampled in allopatry and in sympatry to characterize gene flow in the contact zone. Using genome-wide estimates of diversity, differentiation, and divergence, we find that the degree and direction of introgression varies dramatically across the genome. For sympatric birds, autosomal introgression is bidirectional, with phenotypic hybrids and phenotypic parentals of both species showing admixed ancestry. In other regions of the genome, however, the story is different. While introgression on the Z/neo-Z-linked sequence is limited, introgression of W/neo-W regions and mitochondrial sequence (mtDNA) is highly asymmetric, moving only from the invading M. cardinalis to the resident M. tristrami. The recent hybridization between these species has thus enabled gene flow in some genomic regions but the interaction of admixture, asymmetric mate choice, and/or natural selection has led to the variation in the amount and direction of gene flow at sex-linked regions of the genome.
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Affiliation(s)
- Elsie H. Shogren
- Department of Biology, University of Rochester, Rochester, New York, United States of America
| | - Jason M. Sardell
- PrecisionLife Ltd, Hanborough Business Park, Long Hanborough, Witney, Oxon, United Kingdom
| | - Christina A. Muirhead
- Department of Biology, University of Rochester, Rochester, New York, United States of America
- The Ronin Institute, Montclair, New Jersey, United States of America
| | - Emiliano Martí
- Department of Biology, University of Rochester, Rochester, New York, United States of America
| | - Elizabeth A. Cooper
- Department of Bioinformatics & Genomics, University of North Carolina, Charlotte, North Carolina, United States of America
| | - Robert G. Moyle
- Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas, United States of America
| | - Daven C. Presgraves
- Department of Biology, University of Rochester, Rochester, New York, United States of America
| | - J. Albert C. Uy
- Department of Biology, University of Rochester, Rochester, New York, United States of America
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3
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Mariscal-Ramos C, Cortes-Trujllo I, Martínez-Cortés G, Arana IN, Rangel-Villalobos H. Population expansion, larger, and more homogeneous native American ancestry among Mexican mestizo populations based on 10 X-chromosome STR loci (X-STR decaplex system). Am J Hum Biol 2024:e24124. [PMID: 38978431 DOI: 10.1002/ajhb.24124] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2023] [Revised: 06/17/2024] [Accepted: 06/18/2024] [Indexed: 07/10/2024] Open
Abstract
OBJECTIVE To evaluate the genetic diversity, admixture, genetic relationships, and sex-biased demographic processes in Mexican Mestizo (admixed) populations based on 10 X-chromosome STRs (X-STRs). METHODS We analyzed the X-STRs Decaplex system in 104 Mexican Native Americans to obtain the ancestral reference needed to complete the demographic analyses above mentioned. We included reported Iberian and Latin American (admixed) populations from Central and South America, as well as datasets from Mexican Mestizos based on Y-linked STRs (Y-STRs), autosomal STRs (A-STRs), and mtDNA. RESULTS Higher X-linked Native American ancestry was observed among Latin American populations regarding that reported from A-STRs and Y-STRs. The interpopulation differentiation based on ancestry among Mexican Mestizos diminished according to the inheritance pattern: Y-STRs (highest), A-STRs, X-STRs, and mtDNA (lowest). This finding is related to the peculiar admixture process that occurred during and after the Spanish Conquest of Mexico (and most of Latin America), involving a large number of Spanish men (Y-chromosomes) with a lesser proportion of X-chromosomes than autosomes; besides to the limited number of Spanish women (XX) arrived in the Americas in subsequent and shorter periods. Population expansion was detected in Mexican Mestizos from all the country, except those from the southeast region characterized by elevated indigenous ancestry, marginalization, and poorness. CONCLUSIONS Population growth was detected in most Mexican Mestizos, besides more homogeneous and larger Native American ancestry based on X-linked inheritance than that based on autosomal STRs and Y-STRs.
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Affiliation(s)
- Christian Mariscal-Ramos
- Instituto de Investigación en Genética Molecular, Centro Universitario de la Ciénega, Universidad de Guadalajara (CUCiénega-UdeG), Ocotlán, Jalisco, Mexico
| | - Irán Cortes-Trujllo
- Instituto de Investigación en Genética Molecular, Centro Universitario de la Ciénega, Universidad de Guadalajara (CUCiénega-UdeG), Ocotlán, Jalisco, Mexico
| | - Gabriela Martínez-Cortés
- Instituto de Investigación en Genética Molecular, Centro Universitario de la Ciénega, Universidad de Guadalajara (CUCiénega-UdeG), Ocotlán, Jalisco, Mexico
| | - Ismael Nuño Arana
- Centro de Investigación Multidisciplinario en Salud, Departamento de Salud y Enfermedad, Centro Universitario de Tonalá, Universidad de Guadalajara (CUCiénega-UdeG), Guadalajara, Jalisco, Mexico
| | - Héctor Rangel-Villalobos
- Instituto de Investigación en Genética Molecular, Centro Universitario de la Ciénega, Universidad de Guadalajara (CUCiénega-UdeG), Ocotlán, Jalisco, Mexico
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4
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Edwards SV, Cloutier A, Cockburn G, Driver R, Grayson P, Katoh K, Baldwin MW, Sackton TB, Baker AJ. A nuclear genome assembly of an extinct flightless bird, the little bush moa. SCIENCE ADVANCES 2024; 10:eadj6823. [PMID: 38781323 DOI: 10.1126/sciadv.adj6823] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/10/2023] [Accepted: 04/17/2024] [Indexed: 05/25/2024]
Abstract
We present a draft genome of the little bush moa (Anomalopteryx didiformis)-one of approximately nine species of extinct flightless birds from Aotearoa, New Zealand-using ancient DNA recovered from a fossil bone from the South Island. We recover a complete mitochondrial genome at 249.9× depth of coverage and almost 900 megabases of a male moa nuclear genome at ~4 to 5× coverage, with sequence contiguity sufficient to identify more than 85% of avian universal single-copy orthologs. We describe a diverse landscape of transposable elements and satellite repeats, estimate a long-term effective population size of ~240,000, identify a diverse suite of olfactory receptor genes and an opsin repertoire with sensitivity in the ultraviolet range, show that the wingless moa phenotype is likely not attributable to gene loss or pseudogenization, and identify potential function-altering coding sequence variants in moa that could be synthesized for future functional assays. This genomic resource should support further studies of avian evolution and morphological divergence.
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Affiliation(s)
- Scott V Edwards
- Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA
- Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA
| | - Alison Cloutier
- Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA
| | - Glenn Cockburn
- Evolution of Sensory Systems Research Group, Max Planck Institute for Biological Intelligence, 82319 Seewiesen, Germany
| | - Robert Driver
- Department of Biology, East Carolina University, E 5th Street, Greenville, NC 27605, USA
| | - Phil Grayson
- Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA
- Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA
| | - Kazutaka Katoh
- Department of Genome Informatics, Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita 565-0871, Japan
| | - Maude W Baldwin
- Evolution of Sensory Systems Research Group, Max Planck Institute for Biological Intelligence, 82319 Seewiesen, Germany
| | - Timothy B Sackton
- Informatics Group, Harvard University, 38 Oxford Street, Cambridge, MA 02138, USA
| | - Allan J Baker
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcox Street, Toronto, ON M5S 3B2, Canada
- Department of Natural History, Royal Ontario Museum, 100 Queen's Park, Toronto, ON M5S 2C6, Canada
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5
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van der Valk T, Jensen A, Caillaud D, Guschanski K. Comparative genomic analyses provide new insights into evolutionary history and conservation genomics of gorillas. BMC Ecol Evol 2024; 24:14. [PMID: 38273244 PMCID: PMC10811819 DOI: 10.1186/s12862-023-02195-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2023] [Accepted: 12/22/2023] [Indexed: 01/27/2024] Open
Abstract
Genome sequencing is a powerful tool to understand species evolutionary history, uncover genes under selection, which could be informative of local adaptation, and infer measures of genetic diversity, inbreeding and mutational load that could be used to inform conservation efforts. Gorillas, critically endangered primates, have received considerable attention and with the recently sequenced Bwindi mountain gorilla population, genomic data is now available from all gorilla subspecies and both mountain gorilla populations. Here, we reanalysed this rich dataset with a focus on evolutionary history, local adaptation and genomic parameters relevant for conservation. We estimate a recent split between western and eastern gorillas of 150,000-180,000 years ago, with gene flow around 20,000 years ago, primarily between the Cross River and Grauer's gorilla subspecies. This gene flow event likely obscures evolutionary relationships within eastern gorillas: after excluding putatively introgressed genomic regions, we uncover a sister relationship between Virunga mountain gorillas and Grauer's gorillas to the exclusion of Bwindi mountain gorillas. This makes mountain gorillas paraphyletic. Eastern gorillas are less genetically diverse and more inbred than western gorillas, yet we detected lower genetic load in the eastern species. Analyses of indels fit remarkably well with differences in genetic diversity across gorilla taxa as recovered with nucleotide diversity measures. We also identified genes under selection and unique gene variants specific for each gorilla subspecies, encoding, among others, traits involved in immunity, diet, muscular development, hair morphology and behavior. The presence of this functional variation suggests that the subspecies may be locally adapted. In conclusion, using extensive genomic resources we provide a comprehensive overview of gorilla genomic diversity, including a so-far understudied Bwindi mountain gorilla population, identify putative genes involved in local adaptation, and detect population-specific gene flow across gorilla species.
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Affiliation(s)
- Tom van der Valk
- Centre for Palaeogenetics, Stockholm, Sweden.
- Department of Bioinformatics and Genetics, Swedish Museum of Natural History, Stockholm, Sweden.
- SciLifeLab, Stockholm, Sweden.
- Department of Zoology, Stockholm University, Stockholm, Sweden.
| | - Axel Jensen
- Department of Ecology and Genetics, Animal Ecology, Uppsala University, Uppsala, Sweden
| | - Damien Caillaud
- Department of Anthropology, University of CA - Davis, Davis, California, USA
| | - Katerina Guschanski
- SciLifeLab, Stockholm, Sweden
- Department of Ecology and Genetics, Animal Ecology, Uppsala University, Uppsala, Sweden
- Institute of Ecology and Evolution, School of Biological Sciences, University of Edinburgh, Edinburgh, UK
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6
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Cousins T, Tabin D, Patterson N, Reich D, Durvasula A. Accurate inference of population history in the presence of background selection. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.01.18.576291. [PMID: 38313273 PMCID: PMC10838404 DOI: 10.1101/2024.01.18.576291] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/06/2024]
Abstract
All published methods for learning about demographic history make the simplifying assumption that the genome evolves neutrally, and do not seek to account for the effects of natural selection on patterns of variation. This is a major concern, as ample work has demonstrated the pervasive effects of natural selection and in particular background selection (BGS) on patterns of genetic variation in diverse species. Simulations and theoretical work have shown that methods to infer changes in effective population size over time (Ne(t)) become increasingly inaccurate as the strength of linked selection increases. Here, we introduce an extension to the Pairwise Sequentially Markovian Coalescent (PSMC) algorithm, PSMC+, which explicitly co-models demographic history and natural selection. We benchmark our method using forward-in-time simulations with BGS and find that our approach improves the accuracy of effective population size inference. Leveraging a high resolution map of BGS in humans, we infer considerable changes in the magnitude of inferred effective population size relative to previous reports. Finally, we separately infer Ne(t) on the X chromosome and on the autosomes in diverse great apes without making a correction for selection, and find that the inferred ratio fluctuates substantially through time in a way that differs across species, showing that uncorrected selection may be an important driver of signals of genetic difference on the X chromosome and autosomes.
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Affiliation(s)
- Trevor Cousins
- Department of Human Evolutionary Biology, Harvard University, Cambridge, MA, USA
| | - Daniel Tabin
- Department of Human Evolutionary Biology, Harvard University, Cambridge, MA, USA
| | - Nick Patterson
- Department of Human Evolutionary Biology, Harvard University, Cambridge, MA, USA
- Broad Institute of MIT and Harvard, Cambridge, MA USA
| | - David Reich
- Department of Human Evolutionary Biology, Harvard University, Cambridge, MA, USA
- Broad Institute of MIT and Harvard, Cambridge, MA USA
- Department of Genetics, Harvard Medical School, Boston, MA, USA
- Howard Hughes Medical Institute, Boston, MA, USA
| | - Arun Durvasula
- Department of Human Evolutionary Biology, Harvard University, Cambridge, MA, USA
- Broad Institute of MIT and Harvard, Cambridge, MA USA
- Department of Genetics, Harvard Medical School, Boston, MA, USA
- Department of Epidemiology, Harvard School of Public Health, Boston, MA, USA
- Center for Genetic Epidemiology, Department of Population and Public Health Sciences, Keck School of Medicine, University of Southern California, Los Angeles, CA, USA
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7
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Cotter DJ, Webster TH, Wilson MA. Genomic and demographic processes differentially influence genetic variation across the human X chromosome. PLoS One 2023; 18:e0287609. [PMID: 37910456 PMCID: PMC10619814 DOI: 10.1371/journal.pone.0287609] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Accepted: 06/08/2023] [Indexed: 11/03/2023] Open
Abstract
Many forces influence genetic variation across the genome including mutation, recombination, selection, and demography. Increased mutation and recombination both lead to increases in genetic diversity in a region-specific manner, while complex demographic patterns shape patterns of diversity on a more global scale. While these processes act across the entire genome, the X chromosome is particularly interesting because it contains several distinct regions that are subject to different combinations and strengths of these forces: the pseudoautosomal regions (PARs) and the X-transposed region (XTR). The X chromosome thus can serve as a unique model for studying how genetic and demographic forces act in different contexts to shape patterns of observed variation. We therefore sought to explore diversity, divergence, and linkage disequilibrium in each region of the X chromosome using genomic data from 26 human populations. Across populations, we find that both diversity and substitution rate are consistently elevated in PAR1 and the XTR compared to the rest of the X chromosome. In contrast, linkage disequilibrium is lowest in PAR1, consistent with the high recombination rate in this region, and highest in the region of the X chromosome that does not recombine in males. However, linkage disequilibrium in the XTR is intermediate between PAR1 and the autosomes, and much lower than the non-recombining X. Finally, in addition to these global patterns, we also observed variation in ratios of X versus autosomal diversity consistent with population-specific evolutionary history as well. While our results were generally consistent with previous work, two unexpected observations emerged. First, our results suggest that the XTR does not behave like the rest of the recombining X and may need to be evaluated separately in future studies. Second, the different regions of the X chromosome appear to exhibit unique patterns of linked selection across different human populations. Together, our results highlight profound regional differences across the X chromosome, simultaneously making it an ideal system for exploring the action of evolutionary forces as well as necessitating its careful consideration and treatment in genomic analyses.
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Affiliation(s)
- Daniel J. Cotter
- Department of Genetics, Stanford University, Stanford, CA, United States of America
| | - Timothy H. Webster
- Department of Anthropology, University of Utah, Salt Lake City, UT, United States of America
- School of Life Sciences, Arizona State University, Tempe, AZ, United States of America
| | - Melissa A. Wilson
- School of Life Sciences, Arizona State University, Tempe, AZ, United States of America
- Center for Evolution and Medicine, Biodesign Institute, Arizona State University, Tempe, AZ, United States of America
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8
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Feng S, DeGrey SP, Guédot C, Schoville SD, Pool JE. Genomic Diversity Illuminates the Environmental Adaptation of Drosophila suzukii. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.03.547576. [PMID: 37461625 PMCID: PMC10349955 DOI: 10.1101/2023.07.03.547576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 07/27/2023]
Abstract
Biological invasions carry substantial practical and scientific importance, and represent natural evolutionary experiments on contemporary timescales. Here, we investigated genomic diversity and environmental adaptation of the crop pest Drosophila suzukii using whole-genome sequencing data and environmental metadata for 29 population samples from its native and invasive range. Through a multifaceted analysis of this population genomic data, we increase our understanding of the D. suzukii genome, its diversity and its evolution, and we identify an appropriate genotype-environment association pipeline for our data set. Using this approach, we detect genetic signals of local adaptation associated with nine distinct environmental factors related to altitude, wind speed, precipitation, temperature, and human land use. We uncover unique functional signatures for each environmental variable, such as a prevalence of cuticular genes associated with annual precipitation. We also infer biological commonalities in the adaptation to diverse selective pressures, particularly in terms of the apparent contribution of nervous system evolution to enriched processes (ranging from neuron development to circadian behavior) and to top genes associated with all nine environmental variables. Our findings therefore depict a finer-scale adaptive landscape underlying the rapid invasion success of this agronomically important species.
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Affiliation(s)
- Siyuan Feng
- Laboratory of Genetics, University of Wisconsin-Madison, Madison, WI, USA
| | - Samuel P. DeGrey
- Department of Entomology, University of Wisconsin-Madison, Madison, WI, USA
| | - Christelle Guédot
- Department of Entomology, University of Wisconsin-Madison, Madison, WI, USA
| | - Sean D. Schoville
- Department of Entomology, University of Wisconsin-Madison, Madison, WI, USA
| | - John E. Pool
- Laboratory of Genetics, University of Wisconsin-Madison, Madison, WI, USA
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9
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Näsvall K, Boman J, Höök L, Vila R, Wiklund C, Backström N. Nascent evolution of recombination rate differences as a consequence of chromosomal rearrangements. PLoS Genet 2023; 19:e1010717. [PMID: 37549188 PMCID: PMC10434929 DOI: 10.1371/journal.pgen.1010717] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2023] [Revised: 08/17/2023] [Accepted: 07/17/2023] [Indexed: 08/09/2023] Open
Abstract
Reshuffling of genetic variation occurs both by independent assortment of chromosomes and by homologous recombination. Such reshuffling can generate novel allele combinations and break linkage between advantageous and deleterious variants which increases both the potential and the efficacy of natural selection. Here we used high-density linkage maps to characterize global and regional recombination rate variation in two populations of the wood white butterfly (Leptidea sinapis) that differ considerably in their karyotype as a consequence of at least 27 chromosome fissions and fusions. The recombination data were compared to estimates of genetic diversity and measures of selection to assess the relationship between chromosomal rearrangements, crossing over, maintenance of genetic diversity and adaptation. Our data show that the recombination rate is influenced by both chromosome size and number, but that the difference in the number of crossovers between karyotypes is reduced as a consequence of a higher frequency of double crossovers in larger chromosomes. As expected from effects of selection on linked sites, we observed an overall positive association between recombination rate and genetic diversity in both populations. Our results also revealed a significant effect of chromosomal rearrangements on the rate of intergenic diversity change between populations, but limited effects on polymorphisms in coding sequence. We conclude that chromosomal rearrangements can have considerable effects on the recombination landscape and consequently influence both maintenance of genetic diversity and efficiency of selection in natural populations.
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Affiliation(s)
- Karin Näsvall
- Evolutionary Biology Program, Department of Ecology and Genetics, Uppsala University, Norbyvägen 18D, Uppsala, Sweden
| | - Jesper Boman
- Evolutionary Biology Program, Department of Ecology and Genetics, Uppsala University, Norbyvägen 18D, Uppsala, Sweden
| | - Lars Höök
- Evolutionary Biology Program, Department of Ecology and Genetics, Uppsala University, Norbyvägen 18D, Uppsala, Sweden
| | - Roger Vila
- Butterfly Diversity and Evolution Lab, Institut de Biologia Evolutiva (CSIC-Univ. Pompeu Fabra), Barcelona, Spain
| | - Christer Wiklund
- Department of Zoology: Division of Ecology, Stockholm University, Stockholm, Sweden
| | - Niclas Backström
- Evolutionary Biology Program, Department of Ecology and Genetics, Uppsala University, Norbyvägen 18D, Uppsala, Sweden
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10
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Rivas-González I, Rousselle M, Li F, Zhou L, Dutheil JY, Munch K, Shao Y, Wu D, Schierup MH, Zhang G. Pervasive incomplete lineage sorting illuminates speciation and selection in primates. Science 2023; 380:eabn4409. [PMID: 37262154 DOI: 10.1126/science.abn4409] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2021] [Accepted: 01/19/2023] [Indexed: 06/03/2023]
Abstract
Incomplete lineage sorting (ILS) causes the phylogeny of some parts of the genome to differ from the species tree. In this work, we investigate the frequencies and determinants of ILS in 29 major ancestral nodes across the entire primate phylogeny. We find up to 64% of the genome affected by ILS at individual nodes. We exploit ILS to reconstruct speciation times and ancestral population sizes. Estimated speciation times are much more recent than genomic divergence times and are in good agreement with the fossil record. We show extensive variation of ILS along the genome, mainly driven by recombination but also by the distance to genes, highlighting a major impact of selection on variation along the genome. In many nodes, ILS is reduced more on the X chromosome compared with autosomes than expected under neutrality, which suggests higher impacts of natural selection on the X chromosome. Finally, we show an excess of ILS in genes with immune functions and a deficit of ILS in housekeeping genes. The extensive ILS in primates discovered in this study provides insights into the speciation times, ancestral population sizes, and patterns of natural selection that shape primate evolution.
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Affiliation(s)
- Iker Rivas-González
- Bioinformatics Research Centre, Aarhus University, DK-8000 Aarhus C, Denmark
| | | | - Fang Li
- BGI-Research, BGI-Wuhan, Wuhan 430074, China
- Institute of Animal Sex and Development, ZhejiangWanli University, Ningbo 315104, China
- BGI-Research, BGI-Shenzhen, Shenzhen 518083, China
| | - Long Zhou
- Evolutionary & Organismal Biology Research Center, Zhejiang University School of Medicine, Hangzhou 310058, China
- Women's Hospital, School of Medicine, Zhejiang University, Shangcheng District, Hangzhou 310006, China
| | - Julien Y Dutheil
- Max Planck Institute for Evolutionary Biology, Plön, Germany
- Institute of Evolution Sciences of Montpellier (ISEM), CNRS, University of Montpellier, IRD, EPHE, 34095 Montpellier, France
| | - Kasper Munch
- Bioinformatics Research Centre, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Yong Shao
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan 650223, China
| | - Dongdong Wu
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan 650223, China
- Center for Excellence in Animal Evolution and Genetics, Chinese Academy of Sciences, Kunming, Yunnan 650223, China
- National Resource Center for Non-Human Primates, Kunming Primate Research Center, and National Research Facility for Phenotypic and Genetic Analysis of Model Animals (Primate Facility), Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan 650107, China
- Kunming Natural History Museum of Zoology, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan 650223, China
| | - Mikkel H Schierup
- Bioinformatics Research Centre, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Guojie Zhang
- Evolutionary & Organismal Biology Research Center, Zhejiang University School of Medicine, Hangzhou 310058, China
- Women's Hospital, School of Medicine, Zhejiang University, Shangcheng District, Hangzhou 310006, China
- State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan 650223, China
- Liangzhu Laboratory, Zhejiang University Medical Center, Hangzhou 311121, China
- Villum Centre for Biodiversity Genomics, Section for Ecology and Evolution, Department of Biology, University of Copenhagen, DK-2100 Copenhagen, Denmark
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11
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Skov L, Coll Macià M, Lucotte EA, Cavassim MIA, Castellano D, Schierup MH, Munch K. Extraordinary selection on the human X chromosome associated with archaic admixture. CELL GENOMICS 2023; 3:100274. [PMID: 36950386 PMCID: PMC10025451 DOI: 10.1016/j.xgen.2023.100274] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2022] [Revised: 09/15/2022] [Accepted: 01/26/2023] [Indexed: 03/04/2023]
Abstract
The X chromosome in non-African humans shows less diversity and less Neanderthal introgression than expected from neutral evolution. Analyzing 162 human male X chromosomes worldwide, we identified fourteen chromosomal regions where nearly identical haplotypes spanning several hundred kilobases are found at high frequencies in non-Africans. Genetic drift alone cannot explain the existence of these haplotypes, which must have been associated with strong positive selection in partial selective sweeps. Moreover, the swept haplotypes are entirely devoid of archaic ancestry as opposed to the non-swept haplotypes in the same genomic regions. The ancient Ust'-Ishim male dated at 45,000 before the present (BP) also carries the swept haplotypes, implying that selection on the haplotypes must have occurred between 45,000 and 55,000 years ago. Finally, we find that the chromosomal positions of sweeps overlap previously reported hotspots of selective sweeps in great ape evolution, suggesting a mechanism of selection unique to X chromosomes.
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Affiliation(s)
- Laurits Skov
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720-5800, USA
| | - Moisès Coll Macià
- Bioinformatics Research Centre, Aarhus University, 8000 Aarhus, Denmark
| | - Elise Anne Lucotte
- Ecologie Systématique Evolution, Univ. Paris-Sud, AgroParisTech, CNRS, Université Paris-Saclay, Gif-sur-Yvette, France
| | | | - David Castellano
- Department of Molecular and Cellular Biology, University of Arizona, Tucson, AZ 85721, USA
| | | | - Kasper Munch
- Bioinformatics Research Centre, Aarhus University, 8000 Aarhus, Denmark
- Corresponding author
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12
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Parker DJ, Jaron KS, Dumas Z, Robinson‐Rechavi M, Schwander T. X chromosomes show relaxed selection and complete somatic dosage compensation across
Timema
stick insect species. J Evol Biol 2022; 35:1734-1750. [PMID: 35933721 PMCID: PMC10087215 DOI: 10.1111/jeb.14075] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Revised: 05/06/2022] [Accepted: 07/14/2022] [Indexed: 11/29/2022]
Abstract
Sex chromosomes have evolved repeatedly across the tree of life. As they are present in different copy numbers in males and females, they are expected to experience different selection pressures than the autosomes, with consequences including a faster rate of evolution, increased accumulation of sexually antagonistic alleles and the evolution of dosage compensation. Whether these consequences are general or linked to idiosyncrasies of specific taxa is not clear as relatively few taxa have been studied thus far. Here, we use whole-genome sequencing to identify and characterize the evolution of the X chromosome in five species of Timema stick insects with XX:X0 sex determination. The X chromosome had a similar size (approximately 12% of the genome) and gene content across all five species, suggesting that the X chromosome originated prior to the diversification of the genus. Genes on the X showed evidence of relaxed selection (elevated dN/dS) and a slower evolutionary rate (dN + dS) than genes on the autosomes, likely due to sex-biased mutation rates. Genes on the X also showed almost complete dosage compensation in somatic tissues (heads and legs), but dosage compensation was absent in the reproductive tracts. Contrary to prediction, sex-biased genes showed little enrichment on the X, suggesting that the advantage X-linkage provides to the accumulation of sexually antagonistic alleles is weak. Overall, we found the consequences of X-linkage on gene sequences and expression to be similar across Timema species, showing the characteristics of the X chromosome are surprisingly consistent over 30 million years of evolution.
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Affiliation(s)
- Darren J. Parker
- Department of Ecology and Evolution University of Lausanne Lausanne Switzerland
- Swiss Institute of Bioinformatics Lausanne Switzerland
- School of Natural Sciences Bangor University Bangor UK
| | - Kamil S. Jaron
- Department of Ecology and Evolution University of Lausanne Lausanne Switzerland
- Swiss Institute of Bioinformatics Lausanne Switzerland
- School of Biological Sciences Institute of Evolutionary Biology University of Edinburgh Edinburgh UK
| | - Zoé Dumas
- Department of Ecology and Evolution University of Lausanne Lausanne Switzerland
| | - Marc Robinson‐Rechavi
- Department of Ecology and Evolution University of Lausanne Lausanne Switzerland
- Swiss Institute of Bioinformatics Lausanne Switzerland
| | - Tanja Schwander
- Department of Ecology and Evolution University of Lausanne Lausanne Switzerland
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13
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Robbins RK, Cong Q, Zhang J, Shen J, Busby RC, Faynel C, Duarte M, Martins ARP, Prieto C, Lamas G, Grishin NV. Genomics-based higher classification of the species-rich Hairstreaks (Lepidoptera: Lycaenidae: Eumaeini). SYSTEMATIC ENTOMOLOGY 2022; 47:445-469. [PMID: 35782754 PMCID: PMC9246340 DOI: 10.1111/syen.12541] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
We propose a higher classification of the lycaenid hairstreak tribe Eumaeini - one of the youngest and most species-rich butterfly tribes - based on autosome, Lepidopteran Z sex chromosome, and mitochondrial protein-coding genes. The subtribe Neolycaenina Korb is a synonym of Callophryidina Tutt, and subtribe Tmolusina Bálint is a synonym of Strephonotina K. Johnson, Austin, Le Crom, & Salazar. Proposed names are Rhammina Prieto & Busby, new subtribe; Timaetina Busby & Prieto, new subtribe; Atlidina Martins & Duarte, new subtribe; Evenina Faynel & Grishin, new subtribe; Jantheclina Robbins & Faynel, new subtribe; Paiwarriina Lamas & Robbins, new subtribe; Cupatheclina Lamas & Grishin, new subtribe; Parrhasiina Busby & Robbins, new subtribe; Ipideclina Martins & Grishin, new subtribe; and Trichonidina Duarte & Faynel, new subtribe. Phylogenetic results from the autosome and Z sex chromosome analyses are similar. Future analyses of datasets with hundreds of terminal taxa may be more practical time-wise by focussing on the smaller number of sex chromosome sequences (2.6% of nuclear protein-coding sequences). The phylogenetic classification and biological summaries for each subtribe suggest that a variety of factors affected Eumaeini diversification. About a dozen kinds of male secondary sexual organs with frequent evolutionary gains and losses occur in Atlidina, Evenina, and Jantheclina (141 species combined). Females have been shown to use these organs to discriminate between conspecific and non-conspecific males, facilitating sympatry among close relatives. Eumaeina, Rhammina, and Timaetina (140 species combined) are overwhelmingly montane with some evidence for a higher incidence of sympatric diversification. Seven Neotropical lineages in five subtribes invaded the temperate parts of the Nearctic Region with a diversification increase in the Callophryidina (262 species). North American Satyrium and Callophrys then invaded the Palearctic at least once each, with a major species-richness increase in Satyrium. The evolution of litter feeding detritivores within Calycopidina (172 species) resulted in an increase in diversification rate compared with its flower-feeding sister lineage. Atlidina, Strephonotina, Parrhasiina, and Strymonina (562 species combined) each contain a mixture of genera that specialize on one or two caterpillar food plant families and genera that are polyphagous. These would be appropriate subtribes to assess how the breadth of caterpillar food plants and the frequency of host shifts affected diversification.
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Affiliation(s)
- Robert K Robbins
- Department of Entomology, National Museum of Natural History, PO Box 37012, NHB Stop 105, Smithsonian Institution, Washington, D.C., USA
| | - Qian Cong
- Department of Biochemistry, University of Washington, Seattle, WA, 98105, USA
| | - Jing Zhang
- Department of Biophysics and Biochemistry, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390-8816, USA
| | - Jinhui Shen
- Department of Biophysics and Biochemistry, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390-8816, USA
| | | | | | - Marcelo Duarte
- Museu de Zoologia, Universidade de São Paulo, Avenida Nazaré 481, Ipiranga, 04263-000, São Paulo, SP, Brazil
| | - Ananda R P Martins
- Redpath Museum, McGill University, 859 Sherbrooke Street West, Montreal, Canada, H3A0C4
| | - Carlos Prieto
- Departamento de Biología, Universidad del Atlántico, Barranquilla, Colombia and Corporación Universitaria Autónoma del Cauca, Popayán, Colombia
| | - Gerardo Lamas
- Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Apartado 14-0434, Lima-14, Peru
| | - Nick V Grishin
- Department of Biophysics and Biochemistry, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390-8816, USA
- Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9050, USA
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14
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Booker TR, Payseur BA, Tigano A. Background selection under evolving recombination rates. Proc Biol Sci 2022; 289:20220782. [PMID: 35730151 PMCID: PMC9233929 DOI: 10.1098/rspb.2022.0782] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Background selection (BGS), the effect that purifying selection exerts on sites linked to deleterious alleles, is expected to be ubiquitous across eukaryotic genomes. The effects of BGS reflect the interplay of the rates and fitness effects of deleterious mutations with recombination. A fundamental assumption of BGS models is that recombination rates are invariant over time. However, in some lineages, recombination rates evolve rapidly, violating this central assumption. Here, we investigate how recombination rate evolution affects genetic variation under BGS. We show that recombination rate evolution modifies the effects of BGS in a manner similar to a localized change in the effective population size, potentially leading to underestimation or overestimation of the genome-wide effects of selection. Furthermore, we find evidence that recombination rate evolution in the ancestors of modern house mice may have impacted inferences of the genome-wide effects of selection in that species.
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Affiliation(s)
- Tom R. Booker
- Department of Zoology, University of British Columbia, Vancouver Campus, Vancouver, BC, Canada
| | - Bret A. Payseur
- Laboratory of Genetics, University of Wisconsin - Madison, Madison, WI, USA
| | - Anna Tigano
- Department of Biology, University of British Columbia, Okanagan Campus, Kelowna, BC, Canada
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15
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Kunerth HD, Bogdanowicz SM, Searle JB, Harrison RG, Coates BS, Kozak GM, Dopman EB. Consequences of coupled barriers to gene flow for the build-up of genomic differentiation. Evolution 2022; 76:985-1002. [PMID: 35304922 DOI: 10.1111/evo.14466] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2021] [Revised: 12/09/2021] [Accepted: 12/29/2021] [Indexed: 01/21/2023]
Abstract
Theory predicts that when different barriers to gene flow become coincident, their joint effects enhance reproductive isolation and genomic divergence beyond their individual effects, but empirical tests of this "coupling" hypothesis are rare. Here, we analyze patterns of gene exchange among populations of European corn borer moths that vary in the number of acting barriers, allowing for comparisons of genomic variation when barrier traits or loci are in coincident or independent states. We find that divergence is mainly restricted to barrier loci when populations differ by a single barrier, whereas the coincidence of temporal and behavioral barriers is associated with divergence of two chromosomes harboring barrier loci. Furthermore, differentiation at temporal barrier loci increases in the presence of behavioral divergence and differentiation at behavioral barrier loci increases in the presence of temporal divergence. Our results demonstrate how the joint action of coincident barrier effects leads to levels of genomic differentiation that far exceed those of single barriers acting alone, consistent with theory arguing that coupling allows indirect selection to combine with direct selection and thereby lead to a stronger overall barrier to gene flow. Thus, the state of barriers-independent or coupled-strongly influences the accumulation of genomic differentiation.
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Affiliation(s)
- Henry D Kunerth
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York, 14853
| | - Steven M Bogdanowicz
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York, 14853
| | - Jeremy B Searle
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York, 14853
| | - Richard G Harrison
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York, 14853
| | - Brad S Coates
- Corn Insects and Crop Genetics Research Unit, USDA-ARS, Ames, Iowa, 50011
| | - Genevieve M Kozak
- Department of Biology, University of Massachusetts Dartmouth, Dartmouth, Massachusetts, 02747, USA.,Department of Biology, Tufts University, Medford, Massachusetts, 02155
| | - Erik B Dopman
- Department of Biology, Tufts University, Medford, Massachusetts, 02155
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16
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Oldrieve GR, Malacart B, López-Vidal J, Matthews KR. The genomic basis of host and vector specificity in non-pathogenic trypanosomatids. Biol Open 2022; 11:bio059237. [PMID: 35373253 PMCID: PMC9099014 DOI: 10.1242/bio.059237] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2022] [Accepted: 03/25/2022] [Indexed: 11/20/2022] Open
Abstract
Trypanosoma theileri, a non-pathogenic parasite of bovines, has a predicted surface protein architecture that likely aids survival in its mammalian host. Their surface proteins are encoded by genes which account for ∼10% of their genome. A non-pathogenic parasite of sheep, Trypanosoma melophagium, is transmitted by the sheep ked and is closely related to T. theileri. To explore host and vector specificity between these species, we sequenced the T. melophagium genome and transcriptome and an annotated draft genome was assembled. T. melophagium was compared to 43 kinetoplastid genomes, including T. theileri. T. melophagium and T. theileri have an AT biased genome, the greatest bias of publicly available trypanosomatids. This trend may result from selection acting to decrease the genomic nucleotide cost. The T. melophagium genome is 6.3Mb smaller than T. theileri and large families of proteins, characteristic of the predicted surface of T. theileri, were found to be absent or greatly reduced in T. melophagium. Instead, T. melophagium has modestly expanded protein families associated with the avoidance of complement-mediated lysis. We propose that the contrasting genomic features of these species is linked to their mode of transmission from their insect vector to their mammalian host. This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Guy R. Oldrieve
- Institute of Immunology and Infection Research, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3FL, UK
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17
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Bazzicalupo E, Lucena‐Perez M, Kleinman‐Ruiz D, Pavlov A, Trajçe A, Hoxha B, Sanaja B, Gurielidze Z, Kerdikoshvili N, Mamuchadze J, Yarovenko YA, Akkiev MI, Ratkiewicz M, Saveljev AP, Melovski D, Gavashelishvili A, Schmidt K, Godoy JA. History, demography and genetic status of Balkan and Caucasian
Lynx lynx
(Linnaeus, 1758) populations revealed by genome‐wide variation. DIVERS DISTRIB 2021. [DOI: 10.1111/ddi.13439] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Affiliation(s)
- Enrico Bazzicalupo
- Department of Integrative Ecology Estación Biológica de Doñana (CSIC) Seville Spain
| | - Maria Lucena‐Perez
- Department of Integrative Ecology Estación Biológica de Doñana (CSIC) Seville Spain
| | - Daniel Kleinman‐Ruiz
- Department of Integrative Ecology Estación Biológica de Doñana (CSIC) Seville Spain
| | | | - Aleksandër Trajçe
- Protection and Preservation of Natural Environment in Albania (PPNEA) Tirana Albania
| | - Bledi Hoxha
- Protection and Preservation of Natural Environment in Albania (PPNEA) Tirana Albania
| | - Bardh Sanaja
- Environmentally Responsible Action (ERA) Peje Montenegro
| | - Zurab Gurielidze
- Program for the Ecology and Conservation of Large Mammals Institute of Ecology Ilia State University Tbilisi Georgia
| | - Niko Kerdikoshvili
- Program for the Ecology and Conservation of Large Mammals Institute of Ecology Ilia State University Tbilisi Georgia
| | | | - Yuriy A. Yarovenko
- Pre‐Caspian Institute of Biological Resources Dagestan Federal Scientific Centre of RAS Makhachkala Russian Federation
| | - Muzigit I. Akkiev
- Kabardino‐Balkarian State High‐Mountain Nature Reserve Kashkhatau Russian Federation
| | | | - Alexander P. Saveljev
- Russian Research Institute of Game Management and Fur Farming Kirov Russian Federation
| | - Dime Melovski
- Macedonian Ecological Society (MES) Skopje Macedonia
- Wildlife Sciences Georg‐August University Göttingen Germany
| | | | - Krzysztof Schmidt
- Mammal Research Institute Polish Academy of Sciences Białowieża Poland
| | - José A. Godoy
- Department of Integrative Ecology Estación Biológica de Doñana (CSIC) Seville Spain
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18
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Ruzicka F, Connallon T, Reuter M. Sex differences in deleterious mutational effects in Drosophila melanogaster: combining quantitative and population genetic insights. Genetics 2021; 219:6362879. [PMID: 34740242 DOI: 10.1093/genetics/iyab143] [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: 02/05/2021] [Accepted: 08/25/2021] [Indexed: 11/14/2022] Open
Abstract
Fitness effects of deleterious mutations can differ between females and males due to: (i) sex differences in the strength of purifying selection; and (ii) sex differences in ploidy. Although sex differences in fitness effects have important broader implications (e.g., for the evolution of sex and lifespan), few studies have quantified their scope. Those that have belong to one of two distinct empirical traditions: (i) quantitative genetics, which focusses on multi-locus genetic variances in each sex, but is largely agnostic about their genetic basis; and (ii) molecular population genetics, which focusses on comparing autosomal and X-linked polymorphism, but is poorly suited for inferring contemporary sex differences. Here, we combine both traditions to present a comprehensive analysis of female and male adult reproductive fitness among 202 outbred, laboratory-adapted, hemiclonal genomes of Drosophila melanogaster. While we find no clear evidence for sex differences in the strength of purifying selection, sex differences in ploidy generate multiple signals of enhanced purifying selection for X-linked loci. These signals are present in quantitative genetic metrics-i.e., a disproportionate contribution of the X to male (but not female) fitness variation-and population genetic metrics-i.e., steeper regressions of an allele's average fitness effect on its frequency, and proportionally less nonsynonymous polymorphism on the X than autosomes. Fitting our data to models for both sets of metrics, we infer that deleterious alleles are partially recessive. Given the often-large gap between quantitative and population genetic estimates of evolutionary parameters, our study showcases the benefits of combining genomic and fitness data when estimating such parameters.
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Affiliation(s)
- Filip Ruzicka
- School of Biological Sciences and Centre for Geometric Biology, Monash University, Clayton 3800, VIC, Australia.,Department of Genetics, Evolution and Environment, University College London, London WC1E 6BT, UK
| | - Tim Connallon
- School of Biological Sciences and Centre for Geometric Biology, Monash University, Clayton 3800, VIC, Australia
| | - Max Reuter
- Department of Genetics, Evolution and Environment, University College London, London WC1E 6BT, UK.,Centre for Life's Origins and Evolution, University College London, London WC1E 6BT, UK
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19
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Lucena-Perez M, Kleinman-Ruiz D, Marmesat E, Saveljev AP, Schmidt K, Godoy JA. Bottleneck-associated changes in the genomic landscape of genetic diversity in wild lynx populations. Evol Appl 2021; 14:2664-2679. [PMID: 34815746 PMCID: PMC8591332 DOI: 10.1111/eva.13302] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Revised: 08/17/2021] [Accepted: 09/08/2021] [Indexed: 01/06/2023] Open
Abstract
Demographic bottlenecks generally reduce genetic diversity through more intense genetic drift, but their net effect may vary along the genome due to the random nature of genetic drift and to local effects of recombination, mutation, and selection. Here, we analyzed the changes in genetic diversity following a bottleneck by comparing whole-genome diversity patterns in populations with and without severe recent documented declines of Iberian (Lynx pardinus, n = 31) and Eurasian lynx (Lynx lynx, n = 29). As expected, overall genomic diversity correlated negatively with bottleneck intensity and/or duration. Correlations of genetic diversity with divergence, chromosome size, gene or functional site content, GC content, or recombination were observed in nonbottlenecked populations, but were weaker in bottlenecked populations. Also, functional features under intense purifying selection and the X chromosome showed an increase in the observed density of variants, even resulting in higher θ W diversity than in nonbottlenecked populations. Increased diversity seems to be related to both a higher mutational input in those regions creating a large collection of low-frequency variants, a few of which increase in frequency during the bottleneck to the point they become detectable with our limited sample, and the reduced efficacy of purifying selection, which affects not only protein structure and function but also the regulation of gene expression. The results of this study alert to the possible reduction of fitness and adaptive potential associated with the genomic erosion in regulatory elements. Further, the detection of a gain of diversity in ultra-conserved elements can be used as a sensitive and easy-to-apply signature of genetic erosion in wild populations.
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Affiliation(s)
- Maria Lucena-Perez
- Departamento de Ecología Integrativa Estación Biológica de Doñana (CSIC) Sevilla Spain
| | - Daniel Kleinman-Ruiz
- Departamento de Ecología Integrativa Estación Biológica de Doñana (CSIC) Sevilla Spain
- Departamento de Genética Facultad de Biología Universidad Complutense Madrid Spain
| | - Elena Marmesat
- Departamento de Ecología Integrativa Estación Biológica de Doñana (CSIC) Sevilla Spain
| | - Alexander P Saveljev
- Department of Animal Ecology Russian Research Institute of Game Management and Fur Farming Kirov Russia
| | - Krzysztof Schmidt
- Mammal Research Institute Polish Academy of Sciences Białowieża Poland
| | - José A Godoy
- Departamento de Ecología Integrativa Estación Biológica de Doñana (CSIC) Sevilla Spain
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20
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Mongue AJ, Hansen ME, Walters JR. Support for faster and more adaptive Z chromosome evolution in two divergent lepidopteran lineages. Evolution 2021; 76:332-345. [PMID: 34463346 PMCID: PMC9291949 DOI: 10.1111/evo.14341] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2021] [Revised: 07/21/2021] [Accepted: 08/06/2021] [Indexed: 12/14/2022]
Abstract
The rateof divergence for Z or X chromosomes is usually observed to be greater than autosomes, but the proposed evolutionary causes for this pattern vary, as do empirical results from diverse taxa. Even among moths and butterflies (Lepidoptera), which generally share a single-origin Z chromosome, the handful of available studies give mixed support for faster or more adaptive evolution of the Z chromosome, depending on the species assayed. Here, we examine the molecular evolution of Z chromosomes in two additional lepidopteran species: the Carolina sphinx moth and the monarch butterfly, the latter of which possesses a recent chromosomal fusion yielding a segment of newly Z-linked DNA. We find evidence for both faster and more adaptive Z chromosome evolution in both species, although this effect is strongest in the neo-Z portion of the monarch sex chromosome. The neo-Z is less male-biased than expected of a Z chromosome, and unbiased and female-biased genes drive the signal for adaptive evolution here. Together these results suggest that male-biased gene accumulation and haploid selection have opposing effects on long-term rates of adaptation and may help explain the discrepancies in previous findings as well as the repeated evolution of neo-sex chromosomes in Lepidoptera.
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Affiliation(s)
- Andrew J Mongue
- Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas, 66045.,Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, EH93FL, United Kingdom
| | - Megan E Hansen
- Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas, 66045
| | - James R Walters
- Department of Ecology and Evolutionary Biology, University of Kansas, Lawrence, Kansas, 66045
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21
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Mathur S, DeWoody JA. Genetic load has potential in large populations but is realized in small inbred populations. Evol Appl 2021; 14:1540-1557. [PMID: 34178103 PMCID: PMC8210801 DOI: 10.1111/eva.13216] [Citation(s) in RCA: 44] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 02/25/2021] [Accepted: 03/02/2021] [Indexed: 12/20/2022] Open
Abstract
Populations with higher genetic diversity and larger effective sizes have greater evolutionary capacity (i.e., adaptive potential) to respond to ecological stressors. We are interested in how the variation captured in protein-coding genes fluctuates relative to overall genomic diversity and whether smaller populations suffer greater costs due to their genetic load of deleterious mutations compared with larger populations. We analyzed individual whole-genome sequences (N = 74) from three different populations of Montezuma quail (Cyrtonyx montezumae), a small ground-dwelling bird that is sustainably harvested in some portions of its range but is of conservation concern elsewhere. Our historical demographic results indicate that Montezuma quail populations in the United States exhibit low levels of genomic diversity due in large part to long-term declines in effective population sizes over nearly a million years. The smaller and more isolated Texas population is significantly more inbred than the large Arizona and the intermediate-sized New Mexico populations we surveyed. The Texas gene pool has a significantly smaller proportion of strongly deleterious variants segregating in the population compared with the larger Arizona gene pool. Our results demonstrate that even in small populations, highly deleterious mutations are effectively purged and/or lost due to drift. However, we find that in small populations the realized genetic load is elevated because of inbreeding coupled with a higher frequency of slightly deleterious mutations that are manifested in homozygotes. Overall, our study illustrates how population genomics can be used to proactively assess both neutral and functional aspects of contemporary genetic diversity in a conservation framework while simultaneously considering deeper demographic histories.
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Affiliation(s)
- Samarth Mathur
- Department of Biological SciencesPurdue UniversityWest LafayetteIndianaUSA
- Present address:
Department of Evolution, Ecology and Organismal BiologyThe Ohio State UniversityColumbusOhioUSA
| | - J. Andrew DeWoody
- Department of Biological SciencesPurdue UniversityWest LafayetteIndianaUSA
- Department of Forestry and Natural ResourcesPurdue UniversityWest LafayetteIndianaUSA
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22
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Huang Y, Lack JB, Hoppel GT, Pool JE. Parallel and Population-specific Gene Regulatory Evolution in Cold-Adapted Fly Populations. Genetics 2021; 218:6275754. [PMID: 33989401 PMCID: PMC8864734 DOI: 10.1093/genetics/iyab077] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2020] [Accepted: 05/10/2021] [Indexed: 11/15/2022] Open
Abstract
Changes in gene regulation at multiple levels may comprise an important share of the molecular changes underlying adaptive evolution in nature. However, few studies have assayed within- and between-population variation in gene regulatory traits at a transcriptomic scale, and therefore inferences about the characteristics of adaptive regulatory changes have been elusive. Here, we assess quantitative trait differentiation in gene expression levels and alternative splicing (intron usage) between three closely related pairs of natural populations of Drosophila melanogaster from contrasting thermal environments that reflect three separate instances of cold tolerance evolution. The cold-adapted populations were known to show population genetic evidence for parallel evolution at the SNP level, and here we find evidence for parallel expression evolution between them, with stronger parallelism at larval and adult stages than for pupae. We also implement a flexible method to estimate cis- vs trans-encoded contributions to expression or splicing differences at the adult stage. The apparent contributions of cis- vs trans-regulation to adaptive evolution vary substantially among population pairs. While two of three population pairs show a greater enrichment of cis-regulatory differences among adaptation candidates, trans-regulatory differences are more likely to be implicated in parallel expression changes between population pairs. Genes with significant cis-effects are enriched for signals of elevated genetic differentiation between cold- and warm-adapted populations, suggesting that they are potential targets of local adaptation. These findings expand our knowledge of adaptive gene regulatory evolution and our ability to make inferences about this important and widespread process.
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Affiliation(s)
- Yuheng Huang
- Laboratory of Genetics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.,Department of Ecology and Evolutionary Biology, University of California, Irvine, Irvine, CA 92697, USA
| | - Justin B Lack
- Laboratory of Genetics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.,Advanced Biomedical Computational Science, Frederick National Laboratory for Cancer Research, Frederick, MD 21701, USA
| | - Grant T Hoppel
- Laboratory of Genetics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
| | - John E Pool
- Laboratory of Genetics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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23
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Schield DR, Scordato ESC, Smith CCR, Carter JK, Cherkaoui SI, Gombobaatar S, Hajib S, Hanane S, Hund AK, Koyama K, Liang W, Liu Y, Magri N, Rubtsov A, Sheta B, Turbek SP, Wilkins MR, Yu L, Safran RJ. Sex-linked genetic diversity and differentiation in a globally distributed avian species complex. Mol Ecol 2021; 30:2313-2332. [PMID: 33720472 DOI: 10.1111/mec.15885] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Revised: 02/19/2021] [Accepted: 03/10/2021] [Indexed: 12/15/2022]
Abstract
Sex chromosomes often bear distinct patterns of genetic variation due to unique patterns of inheritance and demography. The processes of mutation, recombination, genetic drift and selection also influence rates of evolution on sex chromosomes differently than autosomes. Measuring such differences provides information about how these processes shape genomic variation and their roles in the origin of species. To test hypotheses and predictions about patterns of autosomal and sex-linked genomic diversity and differentiation, we measured population genetic statistics within and between populations and subspecies of the barn swallow (Hirundo rustica) and performed explicit comparisons between autosomal and Z-linked genomic regions. We first tested for evidence of low Z-linked genetic diversity and high Z-linked population differentiation relative to autosomes, then for evidence that the Z chromosome bears greater ancestry information due to faster lineage sorting. Finally, we investigated geographical clines across hybrid zones for evidence that the Z chromosome is resistant to introgression due to selection against hybrids. We found evidence that the barn swallow mating system, demographic history and linked selection each contribute to low Z-linked diversity and high Z-linked differentiation. While incomplete lineage sorting is rampant across the genome, our results indicate faster sorting of ancestral polymorphism on the Z. Finally, hybrid zone analyses indicate barriers to introgression on the Z chromosome, suggesting that sex-linked traits are important in reproductive isolation, especially in migratory divide regions. Our study highlights how selection, gene flow and demography shape sex-linked genetic diversity and underlines the relevance of the Z chromosome in speciation.
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Affiliation(s)
- Drew R Schield
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA
| | - Elizabeth S C Scordato
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA.,Department of Biological Sciences, California State Polytechnic University, Pomona, CA, USA
| | - Chris C R Smith
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA
| | - Javan K Carter
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA
| | - Sidi Imad Cherkaoui
- Ecole Supérieure de Technologie de Khénifra, Sultan Moulay Slimane University, Béni-Mellal, Morocco
| | - Sundev Gombobaatar
- National University of Mongolia and Mongolian Ornithological Society, Ulaanbaatar, Mongolia
| | - Said Hajib
- Water and Forests Department, Forest Research Center, Rabat-Agdal, Morocco
| | - Saad Hanane
- Water and Forests Department, Forest Research Center, Rabat-Agdal, Morocco
| | - Amanda K Hund
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA.,Department of Ecology, Evolution, and Behavior, University of Minnesota, St. Paul, MN, USA
| | | | - Wei Liang
- Ministry of Education Key Laboratory for Ecology of Tropical Islands, Key Laboratory of Tropical Animal and Plant Ecology of Hainan Province, College of Life Sciences, Hainan Normal University, Haikou, China
| | - Yang Liu
- State Key Laboratory of Biocontrol, School of Ecology, Sun Yat-sen University, Guangzhou, China
| | - Najib Magri
- Water and Forests Department, Forest Research Center, Rabat-Agdal, Morocco
| | | | - Basma Sheta
- Zoology Department, Faculty of Science, Damietta University, New Damietta City, Egypt
| | - Sheela P Turbek
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA
| | - Matthew R Wilkins
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA.,Collaborative for STEM Education and Outreach, Vanderbilt University, Nashville, TN, USA
| | - Liu Yu
- Key Laboratory for Biodiversity Sciences and Ecological Engineering, Ministry of Education, College of Life Sciences, Beijing Normal University, Beijing, China
| | - Rebecca J Safran
- Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA
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24
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Hayes K, Barton HJ, Zeng K. A Study of Faster-Z Evolution in the Great Tit (Parus major). Genome Biol Evol 2021; 12:210-222. [PMID: 32119100 PMCID: PMC7144363 DOI: 10.1093/gbe/evaa044] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/26/2020] [Indexed: 12/17/2022] Open
Abstract
Sex chromosomes contribute substantially to key evolutionary processes such as speciation and adaptation. Several theories suggest that evolution could occur more rapidly on sex chromosomes, but currently our understanding of whether and how this occurs is limited. Here, we present an analysis of the great tit (Parus major) genome, aiming to detect signals of faster-Z evolution. We find mixed evidence of faster divergence on the Z chromosome than autosomes, with significantly higher divergence being found in ancestral repeats, but not at 4- or 0-fold degenerate sites. Interestingly, some 4-fold sites appear to be selectively constrained, which may mislead analyses that use these sites as the neutral reference (e.g., dN/dS). Consistent with other studies in birds, the mutation rate is significantly higher in males than females, and the long-term Z-to-autosome effective population size ratio is only 0.5, significantly lower than the expected value of 0.75. These are indicative of male-driven evolution and high variance in male reproductive success, respectively. We find no evidence for an increased efficacy of positive selection on the Z chromosome. In contrast, the Z chromosome in great tits appears to be affected by increased genetic drift, which has led to detectable signals of weakened intensity of purifying selection. These results provide further evidence that the Z chromosome often has a low effective population size, and that this has important consequences for its evolution. They also highlight the importance of considering multiple factors that can affect the rate of evolution and effective population sizes of sex chromosomes.
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Affiliation(s)
- Kai Hayes
- Department of Animal and Plant Sciences, University of Sheffield, United Kingdom
| | - Henry J Barton
- Department of Animal and Plant Sciences, University of Sheffield, United Kingdom.,Organismal and Evolutionary Biology Research Program, University of Helsinki, Finland
| | - Kai Zeng
- Department of Animal and Plant Sciences, University of Sheffield, United Kingdom
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25
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Johri P, Riall K, Becher H, Excoffier L, Charlesworth B, Jensen JD. The Impact of Purifying and Background Selection on the Inference of Population History: Problems and Prospects. Mol Biol Evol 2021; 38:2986-3003. [PMID: 33591322 PMCID: PMC8233493 DOI: 10.1093/molbev/msab050] [Citation(s) in RCA: 42] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Current procedures for inferring population history generally assume complete neutrality—that is, they neglect both direct selection and the effects of selection on linked sites. We here examine how the presence of direct purifying selection and background selection may bias demographic inference by evaluating two commonly-used methods (MSMC and fastsimcoal2), specifically studying how the underlying shape of the distribution of fitness effects and the fraction of directly selected sites interact with demographic parameter estimation. The results show that, even after masking functional genomic regions, background selection may cause the mis-inference of population growth under models of both constant population size and decline. This effect is amplified as the strength of purifying selection and the density of directly selected sites increases, as indicated by the distortion of the site frequency spectrum and levels of nucleotide diversity at linked neutral sites. We also show how simulated changes in background selection effects caused by population size changes can be predicted analytically. We propose a potential method for correcting for the mis-inference of population growth caused by selection. By treating the distribution of fitness effect as a nuisance parameter and averaging across all potential realizations, we demonstrate that even directly selected sites can be used to infer demographic histories with reasonable accuracy.
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Affiliation(s)
- Parul Johri
- School of Life Sciences, Arizona State University, Tempe, AZ, USA
| | - Kellen Riall
- School of Life Sciences, Arizona State University, Tempe, AZ, USA
| | - Hannes Becher
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Laurent Excoffier
- Institute of Ecology and Evolution, University of Berne, Berne, Switzerland.,Swiss Institute of Bioinformatics, Lausanne, Switzerland
| | - Brian Charlesworth
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Jeffrey D Jensen
- School of Life Sciences, Arizona State University, Tempe, AZ, USA
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26
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Johri P, Riall K, Becher H, Excoffier L, Charlesworth B, Jensen JD. The impact of purifying and background selection on the inference of population history: problems and prospects. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2021. [PMID: 33501439 PMCID: PMC7836109 DOI: 10.1101/2020.04.28.066365] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Current procedures for inferring population history generally assume complete neutrality - that is, they neglect both direct selection and the effects of selection on linked sites. We here examine how the presence of direct purifying selection and background selection may bias demographic inference by evaluating two commonly-used methods (MSMC and fastsimcoal2), specifically studying how the underlying shape of the distribution of fitness effects (DFE) and the fraction of directly selected sites interact with demographic parameter estimation. The results show that, even after masking functional genomic regions, background selection may cause the mis-inference of population growth under models of both constant population size and decline. This effect is amplified as the strength of purifying selection and the density of directly selected sites increases, as indicated by the distortion of the site frequency spectrum and levels of nucleotide diversity at linked neutral sites. We also show how simulated changes in background selection effects caused by population size changes can be predicted analytically. We propose a potential method for correcting for the mis-inference of population growth caused by selection. By treating the DFE as a nuisance parameter and averaging across all potential realizations, we demonstrate that even directly selected sites can be used to infer demographic histories with reasonable accuracy.
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Affiliation(s)
- Parul Johri
- School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA
| | - Kellen Riall
- School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA
| | - Hannes Becher
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, EH9 3FL, United Kingdom
| | - Laurent Excoffier
- Institute of Ecology and Evolution, University of Berne, Berne 3012, Switzerland.,Swiss Institute of Bioinformatics, Lausanne 1015, Switzerland
| | - Brian Charlesworth
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, EH9 3FL, United Kingdom
| | - Jeffrey D Jensen
- School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA
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27
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Charlesworth B. How Good Are Predictions of the Effects of Selective Sweeps on Levels of Neutral Diversity? Genetics 2020; 216:1217-1238. [PMID: 33106248 PMCID: PMC7768247 DOI: 10.1534/genetics.120.303734] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2020] [Accepted: 10/22/2020] [Indexed: 11/18/2022] Open
Abstract
Selective sweeps are thought to play a significant role in shaping patterns of variability across genomes; accurate predictions of their effects are, therefore, important for understanding these patterns. A commonly used model of selective sweeps assumes that alleles sampled at the end of a sweep, and that fail to recombine with wild-type haplotypes during the sweep, coalesce instantaneously, leading to a simple expression for sweep effects on diversity. It is shown here that there can be a significant probability that a pair of alleles sampled at the end of a sweep coalesce during the sweep before a recombination event can occur, reducing their expected coalescent time below that given by the simple approximation. Expressions are derived for the expected reductions in pairwise neutral diversities caused by both single and recurrent sweeps in the presence of such within-sweep coalescence, although the effects of multiple recombination events during a sweep are only treated heuristically. The accuracies of the resulting expressions were checked against the results of simulations. For even moderate ratios of the recombination rate to the selection coefficient, the simple approximation can be substantially inaccurate. The selection model used here can be applied to favorable mutations with arbitrary dominance coefficients, to sex-linked loci with sex-specific selection coefficients, and to inbreeding populations. Using the results from this model, the expected differences between the levels of variability on X chromosomes and autosomes with selection at linked sites are discussed, and compared with data on a population of Drosophila melanogaster.
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Affiliation(s)
- Brian Charlesworth
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, EH9 3FL, United Kingdom
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28
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Changes in life history and population size can explain the relative neutral diversity levels on X and autosomes in extant human populations. Proc Natl Acad Sci U S A 2020; 117:20063-20069. [PMID: 32747577 DOI: 10.1073/pnas.1915664117] [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: 01/17/2023] Open
Abstract
In human populations, the relative levels of neutral diversity on the X and autosomes differ markedly from each other and from the naïve theoretical expectation of 3/4. Here we propose an explanation for these differences based on new theory about the effects of sex-specific life history and given pedigree-based estimates of the dependence of human mutation rates on sex and age. We demonstrate that life history effects, particularly longer generation times in males than in females, are expected to have had multiple effects on human X-to-autosome (X:A) diversity ratios, as a result of male-biased mutation rates, the equilibrium X:A ratio of effective population sizes, and the differential responses to changes in population size. We also show that the standard approach of using divergence between species to correct for male mutation bias results in biased estimates of X:A effective population size ratios. We obtain alternative estimates using pedigree-based estimates of the male mutation bias, which reveal that X:A ratios of effective population sizes are considerably greater than previously appreciated. Finally, we find that the joint effects of historical changes in life history and population size can explain the observed X:A diversity ratios in extant human populations. Our results suggest that ancestral human populations were highly polygynous, that non-African populations experienced a substantial reduction in polygyny and/or increase in the male-to-female ratio of generation times around the Out-of-Africa bottleneck, and that current diversity levels were affected by fairly recent changes in sex-specific life history.
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29
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Life History Effects on Neutral Diversity Levels of Autosomes and Sex Chromosomes. Genetics 2020; 215:1133-1142. [PMID: 32554702 DOI: 10.1534/genetics.120.303119] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Accepted: 06/15/2020] [Indexed: 12/11/2022] Open
Abstract
Understanding the determinants of neutral diversity patterns on autosomes and sex chromosomes provides a bedrock for the interpretation of population genetic data; in particular, differences between the two informs our understanding of sex-specific demographic and mutation processes. While sex-specific age-structure and variation in reproductive success have long been known to affect neutral diversity, theoretical descriptions of these effects were complicated and lacking in generality, stymying attempts to relate diversity patterns of species with their life history. Here, we derive general yet simple expressions for these effects. In particular, we show that life history effects on X-to-autosome ratios of pairwise diversity levels (X:A diversity ratios) depend only on the male-to-female ratios of mutation rates, generation times, and reproductive variances. Our results reveal that changing the male-to-female ratio of generation times has opposite effects on X:A ratios of diversity and divergence. They also explain how sex-specific life histories modulate the response of X:A diversity ratios to changes in population size. More generally, they clarify that sex-specific life history-generation times in particular-should have marked effects on X:A diversity ratios in many taxa and enable further investigation of these effects.
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30
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Phung TN, Wayne RK, Wilson MA, Lohmueller KE. Complex patterns of sex-biased demography in canines. Proc Biol Sci 2020; 286:20181976. [PMID: 31113325 DOI: 10.1098/rspb.2018.1976] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The demographic history of dogs is complex, involving multiple bottlenecks, admixture events and artificial selection. However, existing genetic studies have not explored variance in the number of reproducing males and females, and whether it has changed across evolutionary time. While male-biased mating practices, such as male-biased migration and multiple paternity, have been observed in wolves, recent breeding practices could have led to female-biased mating patterns in breed dogs. For example, breed dogs are thought to have experienced a popular sire effect, where a small number of males father many offspring with a large number of females. Here we use genetic variation data to test how widespread sex-biased mating practices in canines are during different evolutionary time points. Using whole-genome sequence data from 33 dogs and wolves, we show that patterns of diversity on the X chromosome and autosomes are consistent with a higher number of reproducing males than females over ancient evolutionary history in both dogs and wolves, suggesting that mating practices did not change during early dog domestication. By contrast, since breed formation, we found evidence for a larger number of reproducing females than males in breed dogs, consistent with the popular sire effect. Our results confirm that canine demography has been complex, with opposing sex-biased processes occurring throughout their history. The signatures observed in genetic data are consistent with documented sex-biased mating practices in both the wild and domesticated populations, suggesting that these mating practices are pervasive.
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Affiliation(s)
- Tanya N Phung
- 1 Interdepartmental Program in Bioinformatics, University of California , Los Angeles, CA 90095 , USA
| | - Robert K Wayne
- 2 Department of Ecology and Evolutionary Biology, University of California , Los Angeles, CA 90095 , USA
| | - Melissa A Wilson
- 4 School of Life Sciences and Center for Evolution and Medicine, The Biodesign Institute, Arizona State University , Tempe, AZ 85281 , USA
| | - Kirk E Lohmueller
- 1 Interdepartmental Program in Bioinformatics, University of California , Los Angeles, CA 90095 , USA.,2 Department of Ecology and Evolutionary Biology, University of California , Los Angeles, CA 90095 , USA.,3 Department of Human Genetics, David Geffen School of Medicine, University of California , Los Angeles, CA 90095 , USA
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31
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Bourgeois YXC, Bertrand JAM, Delahaie B, Holota H, Thébaud C, Milá B. Differential divergence in autosomes and sex chromosomes is associated with intra-island diversification at a very small spatial scale in a songbird lineage. Mol Ecol 2020; 29:1137-1153. [PMID: 32107807 DOI: 10.1111/mec.15396] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2019] [Revised: 02/12/2020] [Accepted: 02/20/2020] [Indexed: 12/16/2022]
Abstract
Recently diverged taxa showing marked phenotypic and ecological diversity provide optimal systems to understand the genetic processes underlying speciation. We used genome-wide markers to investigate the diversification of the Reunion grey white-eye (Zosterops borbonicus) on the small volcanic island of Reunion (Mascarene archipelago), where this species complex exhibits four geographical forms that are parapatrically distributed across the island and differ strikingly in plumage colour. One form restricted to the highlands is separated by a steep ecological gradient from three distinct lowland forms which meet at narrow hybrid zones that are not associated with environmental variables. Analyses of genomic variation based on single nucleotide polymorphism data from genotyping-by-sequencing and pooled RAD-seq approaches show that signatures of selection associated with elevation can be found at multiple regions across the genome, whereas most loci associated with the lowland forms are located on the Z sex chromosome. We identified TYRP1, a Z-linked colour gene, as a likely candidate locus underlying colour variation among lowland forms. Tests of demographic models revealed that highland and lowland forms diverged in the presence of gene flow, and divergence has progressed as gene flow was restricted by selection at loci across the genome. This system holds promise for investigating how adaptation and reproductive isolation shape the genomic landscape of divergence at multiple stages of the speciation process.
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Affiliation(s)
- Yann X C Bourgeois
- School of Biological Sciences, University of Portsmouth, Portsmouth, UK.,Laboratoire Évolution et Diversité Biologique (EDB), UMR 5174 Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD), Université Paul Sabatier, Toulouse, France
| | - Joris A M Bertrand
- Laboratoire Évolution et Diversité Biologique (EDB), UMR 5174 Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD), Université Paul Sabatier, Toulouse, France.,Laboratoire Génome & Développement des Plantes, UMR 5096, Université de Perpignan Via Domitia, Perpignan, France
| | - Boris Delahaie
- Laboratoire Évolution et Diversité Biologique (EDB), UMR 5174 Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD), Université Paul Sabatier, Toulouse, France.,Department of Plant Sciences, University of Cambridge, Cambridge, UK
| | - Hélène Holota
- Laboratoire Évolution et Diversité Biologique (EDB), UMR 5174 Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD), Université Paul Sabatier, Toulouse, France
| | - Christophe Thébaud
- Laboratoire Évolution et Diversité Biologique (EDB), UMR 5174 Centre National de la Recherche Scientifique (CNRS), Institut de Recherche pour le Développement (IRD), Université Paul Sabatier, Toulouse, France
| | - Borja Milá
- National Museum of Natural Sciences, Spanish National Research Council (CSIC), Madrid, Spain
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32
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Sprengelmeyer QD, Mansourian S, Lange JD, Matute DR, Cooper BS, Jirle EV, Stensmyr MC, Pool JE. Recurrent Collection of Drosophila melanogaster from Wild African Environments and Genomic Insights into Species History. Mol Biol Evol 2020; 37:627-638. [PMID: 31730190 PMCID: PMC7038662 DOI: 10.1093/molbev/msz271] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
A long-standing enigma concerns the geographic and ecological origins of the intensively studied vinegar fly, Drosophila melanogaster. This globally distributed human commensal is thought to originate from sub-Saharan Africa, yet until recently, it had never been reported from undisturbed wilderness environments that could reflect its precommensal niche. Here, we document the collection of 288 D. melanogaster individuals from multiple African wilderness areas in Zambia, Zimbabwe, and Namibia. The presence of D. melanogaster in these remote woodland environments is consistent with an ancestral range in southern-central Africa, as opposed to equatorial regions. After sequencing the genomes of 17 wilderness-collected flies collected from Kafue National Park in Zambia, we found reduced genetic diversity relative to town populations, elevated chromosomal inversion frequencies, and strong differences at specific genes including known insecticide targets. Combining these genomes with existing data, we probed the history of this species' geographic expansion. Demographic estimates indicated that expansion from southern-central Africa began ∼10,000 years ago, with a Saharan crossing soon after, but expansion from the Middle East into Europe did not begin until roughly 1,400 years ago. This improved model of demographic history will provide an important resource for future evolutionary and genomic studies of this key model organism. Our findings add context to the history of D. melanogaster, while opening the door for future studies on the biological basis of adaptation to human environments.
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Affiliation(s)
| | | | - Jeremy D Lange
- Laboratory of Genetics, University of Wisconsin-Madison, Madison, WI
| | - Daniel R Matute
- Department of Biology, University of North Carolina, Chapel Hill, NC
| | - Brandon S Cooper
- Division of Biological Sciences, University of Montana, Missoula, MT
| | | | | | - John E Pool
- Laboratory of Genetics, University of Wisconsin-Madison, Madison, WI
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33
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Lucena-Perez M, Marmesat E, Kleinman-Ruiz D, Martínez-Cruz B, Węcek K, Saveljev AP, Seryodkin IV, Okhlopkov I, Dvornikov MG, Ozolins J, Galsandorj N, Paunovic M, Ratkiewicz M, Schmidt K, Godoy JA. Genomic patterns in the widespread Eurasian lynx shaped by Late Quaternary climatic fluctuations and anthropogenic impacts. Mol Ecol 2020; 29:812-828. [PMID: 31995648 PMCID: PMC7064982 DOI: 10.1111/mec.15366] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Revised: 12/27/2019] [Accepted: 01/16/2020] [Indexed: 12/28/2022]
Abstract
Disentangling the contribution of long-term evolutionary processes and recent anthropogenic impacts to current genetic patterns of wildlife species is key to assessing genetic risks and designing conservation strategies. Here, we used 80 whole nuclear genomes and 96 mitogenomes from populations of the Eurasian lynx covering a range of conservation statuses, climatic zones and subspecies across Eurasia to infer the demographic history, reconstruct genetic patterns, and discuss the influence of long-term isolation and/or more recent human-driven changes. Our results show that Eurasian lynx populations shared a common history until 100,000 years ago, when Asian and European populations started to diverge and both entered a period of continuous and widespread decline, with western populations, except Kirov, maintaining lower effective sizes than eastern populations. Population declines and increased isolation in more recent times probably drove the genetic differentiation between geographically and ecologically close westernmost European populations. By contrast, and despite the wide range of habitats covered, populations are quite homogeneous genetically across the Asian range, showing a pattern of isolation by distance and providing little genetic support for the several proposed subspecies. Mitogenomic and nuclear divergences and population declines starting during the Late Pleistocene can be mostly attributed to climatic fluctuations and early human influence, but the widespread and sustained decline since the Holocene is more probably the consequence of anthropogenic impacts which intensified in recent centuries, especially in western Europe. Genetic erosion in isolated European populations and lack of evidence for long-term isolation argue for the restoration of lost population connectivity.
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Affiliation(s)
- Maria Lucena-Perez
- Department of Integrative Ecology, Estación Biológica de Doñana (CSIC), Seville, Spain
| | - Elena Marmesat
- Department of Integrative Ecology, Estación Biológica de Doñana (CSIC), Seville, Spain
| | - Daniel Kleinman-Ruiz
- Department of Integrative Ecology, Estación Biológica de Doñana (CSIC), Seville, Spain
| | - Begoña Martínez-Cruz
- School of Biological and Environmental Sciences, Liverpool John Moores University, Liverpool, UK
| | - Karolina Węcek
- Mammal Research Institute, Polish Academy of Sciences, Białowieża, Poland
| | - Alexander P Saveljev
- Department of Animal Ecology, Russian Research Institute of Game Management and Fur Farming, Kirov, Russia.,Biological Faculty of Moscow State University, Moscow, Russia
| | - Ivan V Seryodkin
- Laboratory of Ecology and Conservation of Animals, Pacific Institute of Geography of Far East Branch of Russian Academy of Sciences, Vladivostok, Russia.,Far Eastern Federal University, Vladivostok, Russia
| | - Innokentiy Okhlopkov
- Institute for Biological Problems of Cryolithozone, Siberian Division of the Russian Academy of Sciences, Yakutsk, Russia
| | - Mikhail G Dvornikov
- Department of Hunting Resources, Russian Research Institute of Game Management and Fur Farming, Kirov, Russia
| | - Janis Ozolins
- Department of Hunting and Wildlife Management, Latvijas Valsts mežzinātnes institūts "Silava", Salaspils, Latvia
| | - Naranbaatar Galsandorj
- Institute of General and Experimental Biology, Mongolian Academy of Science, Ulaanbaatar, Mongolia
| | | | | | - Krzysztof Schmidt
- Mammal Research Institute, Polish Academy of Sciences, Białowieża, Poland
| | - José A Godoy
- Department of Integrative Ecology, Estación Biológica de Doñana (CSIC), Seville, Spain
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34
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Battey CJ. Evidence of linked selection on the Z chromosome of hybridizing hummingbirds. Evolution 2020; 74:725-739. [PMID: 31859363 DOI: 10.1111/evo.13888] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Revised: 10/01/2019] [Accepted: 11/12/2019] [Indexed: 12/25/2022]
Abstract
Levels of genetic differentiation vary widely along the genomes of recently diverged species. What processes cause this variation? Here, I analyze geographic population structure and genome-wide patterns of variation in the Rufous, Allen's, and Calliope Hummingbirds (Selasphorus rufus/Selasphorus sasin/Selasphorus calliope) and assess evidence that linked selection on the Z chromosome drives patterns of genetic differentiation in a pair of hybridizing species. Demographic models, introgression tests, and genotype clustering analyses support a reticulate evolutionary history consistent with divergence during the late Pleistocene followed by gene flow across migrant Rufous and Allen's Hummingbirds during the Holocene. Relative genetic differentiation ( F s t ) is elevated, and within-population diversity (π) is depressed on the Z chromosome in all interspecific comparisons. The ratio of Z to autosomal within-population diversity is much lower than that expected from population size effects alone, and Tajima's D is depressed on the Z chromosome in S. rufus and S. calliope. These results suggest that conserved structural features of the genome play a prominent role in shaping genetic differentiation through the early stages of speciation in northern Selasphorus hummingbirds, and that the Z chromosome is a likely site of genes underlying behavioral and morphological variation in the group.
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Affiliation(s)
- Christopher J Battey
- Department of Biology, University of Washington, Seattle, Washington, 97403-1201.,Current Address: Institute of Ecology and Evolution, University of Oregon, Eugene, OR, 97403
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35
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The inference of sex-biased human demography from whole-genome data. PLoS Genet 2019; 15:e1008293. [PMID: 31539367 PMCID: PMC6774570 DOI: 10.1371/journal.pgen.1008293] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2018] [Revised: 10/02/2019] [Accepted: 07/07/2019] [Indexed: 01/06/2023] Open
Abstract
Sex-biased demographic events ("sex-bias") involve unequal numbers of females and males. These events are typically inferred from the relative amount of X-chromosomal to autosomal genetic variation and have led to conflicting conclusions about human demographic history. Though population size changes alter the relative amount of X-chromosomal to autosomal genetic diversity even in the absence of sex-bias, this has generally not been accounted for in sex-bias estimators to date. Here, we present a novel method to identify sex-bias from genetic sequence data that models population size changes and estimates the female fraction of the effective population size during each time epoch. Compared to recent sex-bias inference methods, our approach can detect sex-bias that changes on a single population branch without requiring data from an outgroup or knowledge of divergence events. When applied to simulated data, conventional sex-bias estimators are biased by population size changes, especially recent growth or bottlenecks, while our estimator is unbiased. We next apply our method to high-coverage exome data from the 1000 Genomes Project and estimate a male bias in Yorubans (47% female) and Europeans (44%), possibly due to stronger background selection on the X chromosome than on the autosomes. Finally, we apply our method to the 1000 Genomes Project Phase 3 high-coverage Complete Genomics whole-genome data and estimate a female bias in Yorubans (63% female), Europeans (84%), Punjabis (82%), as well as Peruvians (56%), and a male bias in the Southern Han Chinese (45%). Our method additionally identifies a male-biased migration out of Africa based on data from Europeans (20% female). Our results demonstrate that modeling population size change is necessary to estimate sex-bias parameters accurately. Our approach gives insight into signatures of sex-bias in sexual species, and the demographic models it produces can serve as more accurate null models for tests of selection.
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36
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Bechsgaard J, Schou MF, Vanthournout B, Hendrickx F, Knudsen B, Settepani V, Schierup MH, Bilde T. Evidence for Faster X Chromosome Evolution in Spiders. Mol Biol Evol 2019; 36:1281-1293. [PMID: 30912801 PMCID: PMC6526907 DOI: 10.1093/molbev/msz074] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
In species with chromosomal sex determination, X chromosomes are predicted to evolve faster than autosomes because of positive selection on recessive alleles or weak purifying selection. We investigated X chromosome evolution in Stegodyphus spiders that differ in mating system, sex ratio, and population dynamics. We assigned scaffolds to X chromosomes and autosomes using a novel method based on flow cytometry of sperm cells and reduced representation sequencing. We estimated coding substitution patterns (dN/dS) in a subsocial outcrossing species (S. africanus) and its social inbreeding and female-biased sister species (S. mimosarum), and found evidence for faster-X evolution in both species. X chromosome-to-autosome diversity (piX/piA) ratios were estimated in multiple populations. The average piX/piA estimates of S. africanus (0.57 [95% CI: 0.55-0.60]) was lower than the neutral expectation of 0.75, consistent with more hitchhiking events on X-linked loci and/or a lower X chromosome mutation rate, and we provide evidence in support of both. The social species S. mimosarum has a significantly higher piX/piA ratio (0.72 [95% CI: 0.65-0.79]) in agreement with its female-biased sex ratio. Stegodyphus mimosarum also have different piX/piA estimates among populations, which we interpret as evidence for recurrent founder events. Simulations show that recurrent founder events are expected to decrease the piX/piA estimates in S. mimosarum, thus underestimating the true effect of female-biased sex ratios. Finally, we found lower synonymous divergence on X chromosomes in both species, and the male-to-female substitution ratio to be higher than 1, indicating a higher mutation rate in males.
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Affiliation(s)
| | - Mads Fristrup Schou
- Department of Bioscience, Aarhus University, Aarhus C, Denmark.,Department of Biology, Lund University, SE-223 62 Lund, Sweden
| | - Bram Vanthournout
- Department of Bioscience, Aarhus University, Aarhus C, Denmark.,Evolution and Optics of Nanostructure Group (EON), Biology Department, Ghent University, Ghent, Belgium
| | - Frederik Hendrickx
- Royal Belgian Institute of Natural Sciences, Brussels, Belgium.,Terrestrial Ecology Unit (TEREC), Biology Department, Ghent University, Ghent, Belgium
| | | | | | - Mikkel Heide Schierup
- Department of Bioscience, Aarhus University, Aarhus C, Denmark.,Bioinformatics Research Centre (BiRC), Aarhus University, Aarhus C, Denmark
| | - Trine Bilde
- Department of Bioscience, Aarhus University, Aarhus C, Denmark
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37
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Zeng K, Jackson BC, Barton HJ. Methods for Estimating Demography and Detecting Between-Locus Differences in the Effective Population Size and Mutation Rate. Mol Biol Evol 2019; 36:423-433. [PMID: 30428070 PMCID: PMC6409433 DOI: 10.1093/molbev/msy212] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
It is known that the effective population size (Ne) and the mutation rate (u) vary across the genome. Here, we show that ignoring this heterogeneity may lead to biased estimates of past demography. To solve the problem, we develop new methods for jointly inferring past changes in population size and detecting variation in Ne and u between loci. These methods rely on either polymorphism data alone or both polymorphism and divergence data. In addition to inferring demography, we can use the methods to study a variety of questions: 1) comparing sex chromosomes with autosomes (for finding evidence for male-driven evolution, an unequal sex ratio, or sex-biased demographic changes) and 2) analyzing multilocus data from within autosomes or sex chromosomes (for studying determinants of variability in Ne and u). Simulations suggest that the methods can provide accurate parameter estimates and have substantial statistical power for detecting difference in Ne and u. As an example, we use the methods to analyze a polymorphism data set from Drosophila simulans. We find clear evidence for rapid population expansion. The results also indicate that the autosomes have a higher mutation rate than the X chromosome and that the sex ratio is probably female-biased. The new methods have been implemented in a user-friendly package.
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Affiliation(s)
- Kai Zeng
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield, United Kingdom
| | - Benjamin C Jackson
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, United Kingdom
| | - Henry J Barton
- Department of Animal and Plant Sciences, University of Sheffield, Sheffield, United Kingdom
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38
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Arguello JR, Laurent S, Clark AG. Demographic History of the Human Commensal Drosophila melanogaster. Genome Biol Evol 2019; 11:844-854. [PMID: 30715331 PMCID: PMC6430986 DOI: 10.1093/gbe/evz022] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/25/2019] [Indexed: 12/14/2022] Open
Abstract
The cohabitation of Drosophila melanogaster with humans is nearly ubiquitous. Though it has been well established that this fly species originated in sub-Saharan Africa, and only recently has spread globally, many details of its swift expansion remain unclear. Elucidating the demographic history of D. melanogaster provides a unique opportunity to investigate how human movement might have impacted patterns of genetic diversity in a commensal species, as well as providing neutral null models for studies aimed at identifying genomic signatures of local adaptation. Here, we use whole-genome data from five populations (Africa, North America, Europe, Central Asia, and the South Pacific) to carry out demographic inferences, with particular attention to the inclusion of migration and admixture. We demonstrate the importance of these parameters for model fitting and show that how previous estimates of divergence times are likely to be significantly underestimated as a result of not including them. Finally, we discuss how human movement along early shipping routes might have shaped the present-day population structure of D. melanogaster.
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Affiliation(s)
- J Roman Arguello
- Department of Ecology and Evolution, University of Lausanne, Switzerland
| | - Stefan Laurent
- Max Planck Institute for Plant Breeding Research, Köln, Germany
| | - Andrew G Clark
- Department of Molecular Biology and Genetics, Cornell University
- Department of Biological Statistics and Computational Biology, Cornell University
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39
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Pinharanda A, Rousselle M, Martin SH, Hanly JJ, Davey JW, Kumar S, Galtier N, Jiggins CD. Sexually dimorphic gene expression and transcriptome evolution provide mixed evidence for a fast-Z effect in Heliconius. J Evol Biol 2019; 32:194-204. [PMID: 30523653 PMCID: PMC6850379 DOI: 10.1111/jeb.13410] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2018] [Revised: 11/06/2018] [Accepted: 11/27/2018] [Indexed: 12/30/2022]
Abstract
Sex chromosomes have different evolutionary properties compared to autosomes due to their hemizygous nature. In particular, recessive mutations are more readily exposed to selection, which can lead to faster rates of molecular evolution. Here, we report patterns of gene expression and molecular evolution for a group of butterflies. First, we improve the completeness of the Heliconius melpomene reference annotation, a neotropical butterfly with a ZW sex determination system. Then, we analyse RNA from male and female whole abdomens and sequence female ovary and gut tissue to identify sex‐ and tissue‐specific gene expression profiles in H. melpomene. Using these expression profiles, we compare (a) sequence divergence and polymorphism; (b) the strength of positive and negative selection; and (c) rates of adaptive evolution, for Z and autosomal genes between two species of Heliconius butterflies, H. melpomene and H. erato. We show that the rate of adaptive substitutions is higher for Z than autosomal genes, but contrary to expectation, it is also higher for male‐biased than female‐biased genes. Additionally, we find no significant increase in the rate of adaptive evolution or purifying selection on genes expressed in ovary tissue, a heterogametic‐specific tissue. Our results contribute to a growing body of literature from other ZW systems that also provide mixed evidence for a fast‐Z effect where hemizygosity influences the rate of adaptive substitutions.
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Affiliation(s)
- Ana Pinharanda
- Department of Zoology, University of Cambridge, Cambridge, UK.,Department of Ecology and Evolutionary Biology and Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey
| | - Marjolaine Rousselle
- UMR 5554 Institut des Sciences de l'Evolution, CNRS, IRD, EPHE, Université de Montpellier, Montpellier, France
| | - Simon H Martin
- Department of Zoology, University of Cambridge, Cambridge, UK
| | - Joe J Hanly
- Department of Zoology, University of Cambridge, Cambridge, UK
| | - John W Davey
- Department of Zoology, University of Cambridge, Cambridge, UK.,Department of Biology, University of York, York, UK
| | - Sujai Kumar
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, UK
| | - Nicolas Galtier
- Department of Ecology and Evolutionary Biology and Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey
| | - Chris D Jiggins
- Department of Zoology, University of Cambridge, Cambridge, UK
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40
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Janoušek V, Fischerová J, Mořkovský L, Reif J, Antczak M, Albrecht T, Reifová R. Postcopulatory sexual selection reduces Z-linked genetic variation and might contribute to the large Z effect in passerine birds. Heredity (Edinb) 2018; 122:622-635. [PMID: 30374041 DOI: 10.1038/s41437-018-0161-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2018] [Revised: 09/20/2018] [Accepted: 10/12/2018] [Indexed: 12/19/2022] Open
Abstract
The X and Z sex chromosomes play a disproportionately large role in intrinsic postzygotic isolation. The underlying mechanisms of this large X/Z effect are, however, still poorly understood. Here we tested whether faster rates of molecular evolution caused by more intense positive selection or genetic drift on the Z chromosome could contribute to the large Z effect in two closely related passerine birds, the Common Nightingale (Luscinia megarhynchos) and the Thrush Nightingale (L. luscinia). We found that the two species differ in patterns of molecular evolution on the Z chromosome. The Z chromosome of L. megarhynchos showed lower levels of within-species polymorphism and an excess of non-synonymous polymorphisms relative to non-synonymous substitutions. This is consistent with increased levels of genetic drift on this chromosome and may be attributed to more intense postcopulatory sexual selection acting on L. megarhynchos males as was indicated by significantly longer sperm and higher between-male variation in sperm length in L. megarhynchos compared to L. luscinia. Interestingly, analysis of interspecific gene flow on the Z chromosome revealed relatively lower levels of introgression from L. megarhynchos to L. luscinia than vice versa, indicating that the Z chromosome of L. megarhynchos accumulated more hybrid incompatibilities. Our results are consistent with the view that postcopulatory sexual selection may reduce the effective population size of the Z chromosome and thus lead to stronger genetic drift on this chromosome in birds. This can result in relatively faster accumulation of hybrid incompatibilities on the Z and thus contribute to the large Z effect.
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Affiliation(s)
- Václav Janoušek
- Department of Zoology, Faculty of Science, Charles University, Viničná 7, Prague 2, 128 00, Czech Republic
| | - Jitka Fischerová
- Department of Zoology, Faculty of Science, Charles University, Viničná 7, Prague 2, 128 00, Czech Republic
| | - Libor Mořkovský
- Department of Zoology, Faculty of Science, Charles University, Viničná 7, Prague 2, 128 00, Czech Republic
| | - Jiří Reif
- Institute for Environmental Studies, Faculty of Science, Charles University, Benátská 2, Prague 2, 128 01, Czech Republic
| | - Marcin Antczak
- Department of Behavioural Ecology, Adam Mickiewicz University, Umultowska 89, Poznań, 61-614, Poland
| | - Tomáš Albrecht
- Department of Zoology, Faculty of Science, Charles University, Viničná 7, Prague 2, 128 00, Czech Republic.,Institute of Vertebrate Biology, The Czech Academy of Sciences, Květná 8, Brno, 603 65, Czech Republic
| | - Radka Reifová
- Department of Zoology, Faculty of Science, Charles University, Viničná 7, Prague 2, 128 00, Czech Republic.
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41
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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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42
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Presgraves DC. Evaluating genomic signatures of "the large X-effect" during complex speciation. Mol Ecol 2018; 27:3822-3830. [PMID: 29940087 PMCID: PMC6705125 DOI: 10.1111/mec.14777] [Citation(s) in RCA: 74] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2018] [Revised: 05/31/2018] [Accepted: 06/07/2018] [Indexed: 12/16/2022]
Abstract
The ubiquity of the "two rules of speciation"-Haldane's rule and the large X-effect-implies a general, special role for sex chromosomes in the evolution of intrinsic postzygotic reproductive isolation. The recent proliferation of genome-scale analyses has revealed two further general observations: (a) complex speciation involving some form of gene flow is not uncommon, and (b) sex chromosomes in male- and in female-heterogametic taxa tend to show elevated differentiation relative to autosomes. Together, these observations are consistent with speciation histories in which population genetic differentiation at autosomal loci is reduced by gene flow while natural selection against hybrid incompatibilities renders sex chromosomes relatively refractory to gene flow. Here, I summarize multilocus population genetic and population genomic evidence for greater differentiation on the X (or Z) vs. the autosomes and consider the possible causes. I review common population genetic circumstances involving no selection and/or no interspecific gene flow that are nevertheless expected to elevate differentiation on sex chromosomes relative to autosomes. I then review theory for why large X-effects exist for hybrid incompatibilities and, more generally, for loci mediating local adaptation. The observed levels of sex chromosome vs. autosomal differentiation, in many cases, appear consistent with simple explanations requiring neither large X-effects nor gene flow. Discerning signatures of large X-effects during complex speciation will therefore require analyses that go beyond chromosome-scale summaries of population genetic differentiation, explicitly test for differential introgression, and/or integrate experimental genetic data.
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Affiliation(s)
- Daven C. Presgraves
- Department of Biology, University of Rochester, Rochester, New York, 14627, USA
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43
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Support for the Dominance Theory in Drosophila Transcriptomes. Genetics 2018; 210:703-718. [PMID: 30131345 PMCID: PMC6216581 DOI: 10.1534/genetics.118.301229] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2018] [Accepted: 08/10/2018] [Indexed: 12/14/2022] Open
Abstract
Interactions among divergent elements of transcriptional networks from different species can lead to misexpression in hybrids through regulatory incompatibilities, some with the potential to generate sterility. While the possible contribution of faster-male evolution to this misexpression has been explored, the role of the hemizygous X chromosome (i.e., the dominance theory for transcriptomes) remains yet to be determined. Here, we study genome-wide patterns of gene expression in females and males of Drosophila yakuba, Drosophila santomea and their hybrids. We used attached-X stocks to specifically test the dominance theory, and we uncovered a significant contribution of recessive alleles on the X chromosome to hybrid misexpression. Our analyses also suggest a contribution of weakly deleterious regulatory mutations to gene expression divergence in genes with sex-biased expression, but only in the sex toward which the expression is biased (e.g., genes with female-biased expression when analyzed in females). In the opposite sex, we found stronger selective constraints on gene expression divergence. Although genes with a high degree of male-biased expression show a clear signal of faster-X evolution of gene expression, we also detected slower-X evolution in other gene classes (e.g., female-biased genes). This slower-X effect is mediated by significant decreases in cis- and trans-regulatory divergence. The distinct behavior of X-linked genes with a high degree of male-biased expression is consistent with these genes experiencing a higher incidence of positively selected regulatory mutations than their autosomal counterparts.
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44
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Torres R, Szpiech ZA, Hernandez RD. Human demographic history has amplified the effects of background selection across the genome. PLoS Genet 2018; 14:e1007387. [PMID: 29912945 PMCID: PMC6056204 DOI: 10.1371/journal.pgen.1007387] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2017] [Revised: 07/23/2018] [Accepted: 04/30/2018] [Indexed: 01/22/2023] Open
Abstract
Natural populations often grow, shrink, and migrate over time. Such demographic processes can affect genome-wide levels of genetic diversity. Additionally, genetic variation in functional regions of the genome can be altered by natural selection, which drives adaptive mutations to higher frequencies or purges deleterious ones. Such selective processes affect not only the sites directly under selection but also nearby neutral variation through genetic linkage via processes referred to as genetic hitchhiking in the context of positive selection and background selection (BGS) in the context of purifying selection. While there is extensive literature examining the consequences of selection at linked sites at demographic equilibrium, less is known about how non-equilibrium demographic processes influence the effects of hitchhiking and BGS. Utilizing a global sample of human whole-genome sequences from the Thousand Genomes Project and extensive simulations, we investigate how non-equilibrium demographic processes magnify and dampen the consequences of selection at linked sites across the human genome. When binning the genome by inferred strength of BGS, we observe that, compared to Africans, non-African populations have experienced larger proportional decreases in neutral genetic diversity in strong BGS regions. We replicate these findings in admixed populations by showing that non-African ancestral components of the genome have also been affected more severely in these regions. We attribute these differences to the strong, sustained/recurrent population bottlenecks that non-Africans experienced as they migrated out of Africa and throughout the globe. Furthermore, we observe a strong correlation between FST and the inferred strength of BGS, suggesting a stronger rate of genetic drift. Forward simulations of human demographic history with a model of BGS support these observations. Our results show that non-equilibrium demography significantly alters the consequences of selection at linked sites and support the need for more work investigating the dynamic process of multiple evolutionary forces operating in concert.
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Affiliation(s)
- Raul Torres
- Biomedical Sciences Graduate Program, University of California San Francisco, San Francisco, CA, United States of America
| | - Zachary A. Szpiech
- Department of Bioengineering and Therapeutic Sciences, University of California San Francisco, San Francisco, CA, United States of America
| | - Ryan D. Hernandez
- Department of Bioengineering and Therapeutic Sciences, University of California San Francisco, San Francisco, CA, United States of America
- Institute for Human Genetics, University of California San Francisco, San Francisco, CA, United States of America
- Institute for Computational Health Sciences, University of California San Francisco, San Francisco, CA, United States of America
- Quantitative Biosciences Institute, University of California San Francisco, San Francisco, CA, United States of America
- * E-mail:
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45
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Moran PA, Pascoal S, Cezard T, Risse JE, Ritchie MG, Bailey NW. Opposing patterns of intraspecific and interspecific differentiation in sex chromosomes and autosomes. Mol Ecol 2018; 27:3905-3924. [DOI: 10.1111/mec.14725] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2017] [Revised: 04/13/2018] [Accepted: 04/18/2018] [Indexed: 12/24/2022]
Affiliation(s)
- Peter A. Moran
- School of Biological, Earth and Environmental Sciences; University College Cork; Cork Ireland
| | - Sonia Pascoal
- Department of Zoology; University of Cambridge; Cambridge UK
| | | | - Judith E. Risse
- Bioinformatics; Department of Plant Sciences; Wageningen University; Wageningen The Netherlands
| | - Michael G. Ritchie
- Centre for Biological Diversity; School of Biology; University of St Andrews; St Andrews UK
| | - Nathan W. Bailey
- Centre for Biological Diversity; School of Biology; University of St Andrews; St Andrews UK
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46
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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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47
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Llopart A. Faster‐X evolution of gene expression is driven by recessive adaptive
cis
‐regulatory variation in
Drosophila. Mol Ecol 2018; 27:3811-3821. [DOI: 10.1111/mec.14708] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2017] [Revised: 03/28/2018] [Accepted: 04/05/2018] [Indexed: 12/30/2022]
Affiliation(s)
- Ana Llopart
- Department of Biology The University of Iowa Iowa City Iowa
- Interdisciplinary Graduate Program in Genetics The University of Iowa Iowa City Iowa
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48
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Van Belleghem SM, Baquero M, Papa R, Salazar C, McMillan WO, Counterman BA, Jiggins CD, Martin SH. Patterns of Z chromosome divergence among Heliconius species highlight the importance of historical demography. Mol Ecol 2018; 27:3852-3872. [PMID: 29569384 PMCID: PMC6151167 DOI: 10.1111/mec.14560] [Citation(s) in RCA: 43] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Revised: 02/14/2018] [Accepted: 02/20/2018] [Indexed: 12/31/2022]
Abstract
Sex chromosomes are disproportionately involved in reproductive isolation and adaptation. In support of such a “large‐X” effect, genome scans between recently diverged populations and species pairs often identify distinct patterns of divergence on the sex chromosome compared to autosomes. When measures of divergence between populations are higher on the sex chromosome compared to autosomes, such patterns could be interpreted as evidence for faster divergence on the sex chromosome, that is “faster‐X”, barriers to gene flow on the sex chromosome. However, demographic changes can strongly skew divergence estimates and are not always taken into consideration. We used 224 whole‐genome sequences representing 36 populations from two Heliconius butterfly clades (H. erato and H. melpomene) to explore patterns of Z chromosome divergence. We show that increased divergence compared to equilibrium expectations can in many cases be explained by demographic change. Among Heliconius erato populations, for instance, population size increase in the ancestral population can explain increased absolute divergence measures on the Z chromosome compared to the autosomes, as a result of increased ancestral Z chromosome genetic diversity. Nonetheless, we do identify increased divergence on the Z chromosome relative to the autosomes in parapatric or sympatric species comparisons that imply postzygotic reproductive barriers. Using simulations, we show that this is consistent with reduced gene flow on the Z chromosome, perhaps due to greater accumulation of incompatibilities. Our work demonstrates the importance of taking demography into account to interpret patterns of divergence on the Z chromosome, but nonetheless provides evidence to support the Z chromosome as a strong barrier to gene flow in incipient Heliconius butterfly species.
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Affiliation(s)
- Steven M Van Belleghem
- Department of Zoology, University of Cambridge, Cambridge, UK.,Department of Biological Sciences, Mississippi State University, Mississippi State, MS, USA.,Department of Biology, Center for Applied Tropical Ecology and Conservation, University of Puerto Rico, Rio Piedras, Puerto Rico.,Smithsonian Tropical Research Institute, Apartado, Panamá, Panama
| | - Margarita Baquero
- Department of Biological Sciences, Mississippi State University, Mississippi State, MS, USA
| | - Riccardo Papa
- Department of Biology, Center for Applied Tropical Ecology and Conservation, University of Puerto Rico, Rio Piedras, Puerto Rico
| | - Camilo Salazar
- Biology Program, Faculty of Natural Sciences and Mathematics, Universidad del Rosario, Carrera, Bogota, Colombia
| | - W Owen McMillan
- Smithsonian Tropical Research Institute, Apartado, Panamá, Panama
| | - Brian A Counterman
- Department of Biological Sciences, Mississippi State University, Mississippi State, MS, USA
| | - Chris D Jiggins
- Department of Zoology, University of Cambridge, Cambridge, UK
| | - Simon H Martin
- Department of Zoology, University of Cambridge, Cambridge, UK
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Irwin DE. Sex chromosomes and speciation in birds and other ZW systems. Mol Ecol 2018; 27:3831-3851. [PMID: 29443419 DOI: 10.1111/mec.14537] [Citation(s) in RCA: 65] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2017] [Revised: 02/03/2018] [Accepted: 02/06/2018] [Indexed: 01/01/2023]
Abstract
Theory and empirical patterns suggest a disproportionate role for sex chromosomes in evolution and speciation. Focusing on ZW sex determination (females ZW, males ZZ; the system in birds, many snakes, and lepidopterans), I review how evolutionary dynamics are expected to differ between the Z, W and the autosomes, discuss how these differences may lead to a greater role of the sex chromosomes in speciation and use data from birds to compare relative evolutionary rates of sex chromosomes and autosomes. Neutral mutations, partially or completely recessive beneficial mutations, and deleterious mutations under many conditions are expected to accumulate faster on the Z than on autosomes. Sexually antagonistic polymorphisms are expected to arise on the Z, raising the possibility of the spread of preference alleles. The faster accumulation of many types of mutations and the potential for complex evolutionary dynamics of sexually antagonistic traits and preferences contribute to a role for the Z chromosome in speciation. A quantitative comparison among a wide variety of bird species shows that the Z tends to have less within-population diversity and greater between-species differentiation than the autosomes, likely due to both adaptive evolution and a greater rate of fixation of deleterious alleles. The W chromosome also shows strong potential to be involved in speciation, in part because of its co-inheritance with the mitochondrial genome. While theory and empirical evidence suggest a disproportionate role for sex chromosomes in speciation, the importance of sex chromosomes is moderated by their small size compared to the whole genome.
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Affiliation(s)
- Darren E Irwin
- Department of Zoology and Biodiversity Research Centre, University of British Columbia, Vancouver, BC, Canada
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Charlesworth B, Campos JL, Jackson BC. Faster-X evolution: Theory and evidence from Drosophila. Mol Ecol 2018; 27:3753-3771. [PMID: 29431881 DOI: 10.1111/mec.14534] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2017] [Revised: 01/31/2018] [Accepted: 02/06/2018] [Indexed: 12/13/2022]
Abstract
A faster rate of adaptive evolution of X-linked genes compared with autosomal genes can be caused by the fixation of recessive or partially recessive advantageous mutations, due to the full expression of X-linked mutations in hemizygous males. Other processes, including recombination rate and mutation rate differences between X chromosomes and autosomes, may also cause faster evolution of X-linked genes. We review population genetics theory concerning the expected relative values of variability and rates of evolution of X-linked and autosomal DNA sequences. The theoretical predictions are compared with data from population genomic studies of several species of Drosophila. We conclude that there is evidence for adaptive faster-X evolution of several classes of functionally significant nucleotides. We also find evidence for potential differences in mutation rates between X-linked and autosomal genes, due to differences in mutational bias towards GC to AT mutations. Many aspects of the data are consistent with the male hemizygosity model, although not all possible confounding factors can be excluded.
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Affiliation(s)
- Brian Charlesworth
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, UK
| | - José L Campos
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, UK
| | - Benjamin C Jackson
- Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh, UK
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