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Hugall AF, Byrne M, O'Hara TD. Genetic variation in the brooding brittle-star: a global hybrid polyploid complex? ROYAL SOCIETY OPEN SCIENCE 2024; 11:240428. [PMID: 39113777 PMCID: PMC11304335 DOI: 10.1098/rsos.240428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/20/2024] [Revised: 07/10/2024] [Accepted: 07/10/2024] [Indexed: 08/10/2024]
Abstract
The widespread and abundant brooding brittle-star (Amphipholis squamata) is a simultaneous hermaphrodite with a complex mitochondrial phylogeography of multiple divergent overlapping mtDNA lineages, high levels of inbreeding or clonality and unusual sperm morphology. We use exon-capture and transcriptome data to show that the nuclear genome comprises multiple (greater than 3) divergent (π > 6%) expressed components occurring across samples characterized by highly divergent (greater than 20%) mitochondrial lineages, and encompassing several other genera, including diploid dioecious species. We report a massive sperm genome size in A. squamata, an order of magnitude larger than that present in other brittle-stars, and consistent with our SNP-based measure of greatly elevated ploidy. Similarity of these genetic signatures to well-known animal systems suggests that A. squamata (and related taxa) is a hybrid polyploid asexual complex of variable subgenome origins, ploidy and reproductive mode. We discuss enigmatic aspects of A. squamata biology in this light. This putative allopolyploid complex would be the first to be reported from the phylum Echinodermata.
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Affiliation(s)
- Andrew F. Hugall
- Museums Victoria, GPO Box 666, Melbourne, Victoria3001, Australia
| | - Maria Byrne
- School of Life and Environmental Science, University of Sydney, Camperdown, New South Wales2050, Australia
| | - Timothy D. O'Hara
- School of Life and Environmental Science, University of Sydney, Camperdown, New South Wales2050, Australia
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2
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Nowell RW, Rodriguez F, Hecox-Lea BJ, Mark Welch DB, Arkhipova IR, Barraclough TG, Wilson CG. Bdelloid rotifers deploy horizontally acquired biosynthetic genes against a fungal pathogen. Nat Commun 2024; 15:5787. [PMID: 39025839 PMCID: PMC11258130 DOI: 10.1038/s41467-024-49919-1] [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: 05/16/2023] [Accepted: 06/18/2024] [Indexed: 07/20/2024] Open
Abstract
Coevolutionary antagonism generates relentless selection that can favour genetic exchange, including transfer of antibiotic synthesis and resistance genes among bacteria, and sexual recombination of disease resistance alleles in eukaryotes. We report an unusual link between biological conflict and DNA transfer in bdelloid rotifers, microscopic animals whose genomes show elevated levels of horizontal gene transfer from non-metazoan taxa. When rotifers were challenged with a fungal pathogen, horizontally acquired genes were over twice as likely to be upregulated as other genes - a stronger enrichment than observed for abiotic stressors. Among hundreds of upregulated genes, the most markedly overrepresented were clusters resembling bacterial polyketide and nonribosomal peptide synthetases that produce antibiotics. Upregulation of these clusters in a pathogen-resistant rotifer species was nearly ten times stronger than in a susceptible species. By acquiring, domesticating, and expressing non-metazoan biosynthetic pathways, bdelloids may have evolved to resist natural enemies using antimicrobial mechanisms absent from other animals.
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Affiliation(s)
- Reuben W Nowell
- Department of Biology, University of Oxford, 11a Mansfield Road, Oxford, OX1 3SZ, UK
- Department of Life Sciences, Imperial College London; Silwood Park Campus, Buckhurst Road, Ascot, Berkshire, SL5 7PY, UK
- Institute of Ecology and Evolution, University of Edinburgh; Ashworth Laboratories, Charlotte Auerbach Road, Edinburgh, EH9 3FL, UK
- Biological and Environmental Sciences, University of Stirling, Stirling, FK9 4LA, UK
| | - Fernando Rodriguez
- Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, MA, USA
| | - Bette J Hecox-Lea
- Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, MA, USA
| | - David B Mark Welch
- Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, MA, USA
| | - Irina R Arkhipova
- Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory, Woods Hole, MA, USA
| | - Timothy G Barraclough
- Department of Biology, University of Oxford, 11a Mansfield Road, Oxford, OX1 3SZ, UK
- Department of Life Sciences, Imperial College London; Silwood Park Campus, Buckhurst Road, Ascot, Berkshire, SL5 7PY, UK
| | - Christopher G Wilson
- Department of Biology, University of Oxford, 11a Mansfield Road, Oxford, OX1 3SZ, UK.
- Department of Life Sciences, Imperial College London; Silwood Park Campus, Buckhurst Road, Ascot, Berkshire, SL5 7PY, UK.
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3
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Wilson CG, Pieszko T, Nowell RW, Barraclough TG. Recombination in bdelloid rotifer genomes: asexuality, transfer and stress. Trends Genet 2024; 40:422-436. [PMID: 38458877 DOI: 10.1016/j.tig.2024.02.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2023] [Revised: 01/31/2024] [Accepted: 02/01/2024] [Indexed: 03/10/2024]
Abstract
Bdelloid rotifers constitute a class of microscopic animals living in freshwater habitats worldwide. Several strange features of bdelloids have drawn attention: their ability to tolerate desiccation and other stresses, a lack of reported males across the clade despite centuries of study, and unusually high numbers of horizontally acquired, non-metazoan genes. Genome sequencing is transforming our understanding of their lifestyle and its consequences, while in turn providing wider insights about recombination and genome organisation in animals. Many questions remain, not least how to reconcile apparent genomic signatures of sex with the continued absence of reported males, why bdelloids have so many horizontally acquired genes, and how their remarkable ability to survive stress interacts with recombination and other genomic processes.
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Affiliation(s)
- Christopher G Wilson
- Department of Biology, University of Oxford, 11a Mansfield Road, Oxford OX1 3SZ, UK.
| | - Tymoteusz Pieszko
- Department of Biology, University of Oxford, 11a Mansfield Road, Oxford OX1 3SZ, UK
| | - Reuben W Nowell
- Institute of Ecology and Evolution, Ashworth Laboratories, Charlotte Auerbach Road, Edinburgh EH9 3FL, UK; Biological and Environmental Sciences, School of Natural Sciences, University of Stirling, Stirling FK9 4LA, UK
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4
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Krueger-Hadfield SA, Shainker-Connelly SJ, Crowell RM, Vis ML. The eco-evolutionary importance of reproductive system variation in the macroalgae: Freshwater reds as a case study. JOURNAL OF PHYCOLOGY 2024; 60:15-25. [PMID: 37948315 DOI: 10.1111/jpy.13407] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Revised: 10/15/2023] [Accepted: 10/18/2023] [Indexed: 11/12/2023]
Abstract
The relative frequency of sexual versus asexual reproduction governs the distribution of genetic diversity within and among populations. Most studies on the consequences of reproductive variation focus on the mating system (i.e., selfing vs. outcrossing) of diploid-dominant taxa (e.g., angiosperms), often ignoring asexual reproduction. Although reproductive systems are hypothesized to be correlated with life-cycle types, variation in the relative rates of sexual and asexual reproduction remains poorly characterized across eukaryotes. This is particularly true among the three major lineages of macroalgae (green, brown, and red). The Rhodophyta are particularly interesting, as many taxa have complex haploid-diploid life cycles that influence genetic structure. Though most marine reds have separate sexes, we show that freshwater red macroalgae exhibit patterns of switching between monoicy and dioicy in sister taxa that rival those recently shown in brown macroalgae and in angiosperms. We advocate for the investigation of reproductive system evolution using freshwater reds, as this will expand the life-cycle types for which these data exist, enabling comparative analyses broadly across eukaryotes. Unlike their marine cousins, species in the Batrachospermales have macroscopic gametophytes attached to filamentous, often microscopic sporophytes. While asexual reproduction through monospores may occur in all freshwater reds, the Compsopogonales are thought to be exclusively asexual. Understanding the evolutionary consequences of selfing and asexual reproduction will aid in our understanding of the evolutionary ecology of all algae and of eukaryotic evolution generally.
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Affiliation(s)
| | | | - Roseanna M Crowell
- Department of Environmental and Plant Biology, Ohio University, Athens, Ohio, USA
| | - Morgan L Vis
- Department of Environmental and Plant Biology, Ohio University, Athens, Ohio, USA
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5
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Rogers TF, Simakov O. Emerging questions on the mechanisms and dynamics of 3D genome evolution in spiralians. Brief Funct Genomics 2023; 22:533-542. [PMID: 37815133 PMCID: PMC10658181 DOI: 10.1093/bfgp/elad043] [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: 04/29/2023] [Revised: 08/17/2023] [Accepted: 09/12/2023] [Indexed: 10/11/2023] Open
Abstract
Information on how 3D genome topology emerged in animal evolution, how stable it is during development, its role in the evolution of phenotypic novelties and how exactly it affects gene expression is highly debated. So far, data to address these questions are lacking with the exception of a few key model species. Several gene regulatory mechanisms have been proposed, including scenarios where genome topology has little to no impact on gene expression, and vice versa. The ancient and diverse clade of spiralians may provide a crucial testing ground for such mechanisms. Sprialians have followed distinct evolutionary trajectories, with some clades experiencing genome expansions and/or large-scale genome rearrangements, and others undergoing genome contraction, substantially impacting their size and organisation. These changes have been associated with many phenotypic innovations in this clade. In this review, we describe how emerging genome topology data, along with functional tools, allow for testing these scenarios and discuss their predicted outcomes.
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Affiliation(s)
- Thea F Rogers
- Department of Neuroscience and Developmental Biology, Division of Molecular Evolution and Development, University of Vienna, Vienna, Austria
| | - Oleg Simakov
- Department of Neuroscience and Developmental Biology, Division of Molecular Evolution and Development, University of Vienna, Vienna, Austria
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6
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Freitas S, Parker DJ, Labédan M, Dumas Z, Schwander T. Evidence for cryptic sex in parthenogenetic stick insects of the genus Timema. Proc Biol Sci 2023; 290:20230404. [PMID: 37727092 PMCID: PMC10509586 DOI: 10.1098/rspb.2023.0404] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Accepted: 08/23/2023] [Indexed: 09/21/2023] Open
Abstract
Obligately parthenogenetic species are expected to be short lived since the lack of sex and recombination should translate into a slower adaptation rate and increased accumulation of deleterious alleles. Some, however, are thought to have been reproducing without males for millions of years. It is not clear how these old parthenogens can escape the predicted long-term costs of parthenogenesis, but an obvious explanation is cryptic sex. In this study, we screen for signatures of cryptic sex in eight populations of four parthenogenetic species of Timema stick insects, some estimated to be older than 1 Myr. Low genotype diversity, homozygosity of individuals and high linkage disequilibrium (LD) unaffected by marker distances support exclusively parthenogenetic reproduction in six populations. However, in two populations (namely, of the species Timema douglasi and T. monikensis) we find strong evidence for cryptic sex, most likely mediated by rare males. These populations had comparatively high genotype diversities, lower LD, and a clear LD decay with genetic distance. Rare sex in species that are otherwise largely parthenogenetic could help explain the unusual success of parthenogenesis in the Timema genus and raises the question whether episodes of rare sex are in fact the simplest explanation for the persistence of many old parthenogens in nature.
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Affiliation(s)
- Susana Freitas
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
| | - Darren J. Parker
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
- School of Natural Sciences, Bangor University, Bangor, UK
| | - Marjorie Labédan
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
| | - Zoé Dumas
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
| | - Tanja Schwander
- Department of Ecology and Evolution, University of Lausanne, Lausanne, Switzerland
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7
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Zhou J, Horton JR, Kaur G, Chen Q, Li X, Mendoza F, Wu T, Blumenthal RM, Zhang X, Cheng X. Biochemical and structural characterization of the first-discovered metazoan DNA cytosine-N4 methyltransferase from the bdelloid rotifer Adineta vaga. J Biol Chem 2023; 299:105017. [PMID: 37414145 PMCID: PMC10406627 DOI: 10.1016/j.jbc.2023.105017] [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: 05/26/2023] [Revised: 06/27/2023] [Accepted: 06/29/2023] [Indexed: 07/08/2023] Open
Abstract
Much is known about the generation, removal, and roles of 5-methylcytosine (5mC) in eukaryote DNA, and there is a growing body of evidence regarding N6-methyladenine, but very little is known about N4-methylcytosine (4mC) in the DNA of eukaryotes. The gene for the first metazoan DNA methyltransferase generating 4mC (N4CMT) was reported and characterized recently by others, in tiny freshwater invertebrates called bdelloid rotifers. Bdelloid rotifers are ancient, apparently asexual animals, and lack canonical 5mC DNA methyltransferases. Here, we characterize the kinetic properties and structural features of the catalytic domain of the N4CMT protein from the bdelloid rotifer Adineta vaga. We find that N4CMT generates high-level methylation at preferred sites, (a/c)CG(t/c/a), and low-level methylation at disfavored sites, exemplified by ACGG. Like the mammalian de novo 5mC DNA methyltransferase 3A/3B (DNMT3A/3B), N4CMT methylates CpG dinucleotides on both DNA strands, generating hemimethylated intermediates and eventually fully methylated CpG sites, particularly in the context of favored symmetric sites. In addition, like DNMT3A/3B, N4CMT methylates non-CpG sites, mainly CpA/TpG, though at a lower rate. Both N4CMT and DNMT3A/3B even prefer similar CpG-flanking sequences. Structurally, the catalytic domain of N4CMT closely resembles the Caulobacter crescentus cell cycle-regulated DNA methyltransferase. The symmetric methylation of CpG, and similarity to a cell cycle-regulated DNA methyltransferase, together suggest that N4CMT might also carry out DNA synthesis-dependent methylation following DNA replication.
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Affiliation(s)
- Jujun Zhou
- Department of Epigenetics and Molecular Carcinogenesis, University of Texas MD Anderson Cancer Center, Houston, Texas, USA
| | - John R Horton
- Department of Epigenetics and Molecular Carcinogenesis, University of Texas MD Anderson Cancer Center, Houston, Texas, USA
| | - Gundeep Kaur
- Department of Epigenetics and Molecular Carcinogenesis, University of Texas MD Anderson Cancer Center, Houston, Texas, USA
| | - Qin Chen
- Department of Epigenetics and Molecular Carcinogenesis, University of Texas MD Anderson Cancer Center, Houston, Texas, USA
| | - Xuwen Li
- Department of Molecular & Human Genetics, Baylor College of Medicine, Houston, Texas, USA
| | - Fabian Mendoza
- Department of Epigenetics and Molecular Carcinogenesis, University of Texas MD Anderson Cancer Center, Houston, Texas, USA
| | - Tao Wu
- Department of Molecular & Human Genetics, Baylor College of Medicine, Houston, Texas, USA
| | - Robert M Blumenthal
- Department of Medical Microbiology and Immunology, Program in Bioinformatics, The University of Toledo College of Medicine and Life Sciences, Toledo, Ohio, USA.
| | - Xing Zhang
- Department of Epigenetics and Molecular Carcinogenesis, University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
| | - Xiaodong Cheng
- Department of Epigenetics and Molecular Carcinogenesis, University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
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8
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Yadav V, Sun S, Heitman J. On the evolution of variation in sexual reproduction through the prism of eukaryotic microbes. Proc Natl Acad Sci U S A 2023; 120:e2219120120. [PMID: 36867686 PMCID: PMC10013875 DOI: 10.1073/pnas.2219120120] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2022] [Accepted: 01/23/2023] [Indexed: 03/05/2023] Open
Abstract
Almost all eukaryotes undergo sexual reproduction to generate diversity and select for fitness in their population pools. Interestingly, the systems by which sex is defined are highly diverse and can even differ between evolutionarily closely related species. While the most commonly known form of sex determination involves males and females in animals, eukaryotic microbes can have as many as thousands of different mating types for the same species. Furthermore, some species have found alternatives to sexual reproduction and prefer to grow clonally and yet undergo infrequent facultative sexual reproduction. These organisms are mainly invertebrates and microbes, but several examples are also present among vertebrates suggesting that alternative modes of sexual reproduction evolved multiple times throughout evolution. In this review, we summarize the sex-determination modes and variants of sexual reproduction found across the eukaryotic tree of life and suggest that eukaryotic microbes provide unique opportunities to study these processes in detail. We propose that understanding variations in modes of sexual reproduction can serve as a foundation to study the evolution of sex and why and how it evolved in the first place.
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Affiliation(s)
- Vikas Yadav
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC27710
| | - Sheng Sun
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC27710
| | - Joseph Heitman
- Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC27710
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9
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Terwagne M, Nicolas E, Hespeels B, Herter L, Virgo J, Demazy C, Heuskin AC, Hallet B, Van Doninck K. DNA repair during nonreductional meiosis in the asexual rotifer Adineta vaga. SCIENCE ADVANCES 2022; 8:eadc8829. [PMID: 36449626 PMCID: PMC9710870 DOI: 10.1126/sciadv.adc8829] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/06/2022] [Accepted: 10/13/2022] [Indexed: 06/17/2023]
Abstract
Rotifers of the class Bdelloidea are microscopic animals notorious for their long-term persistence in the apparent absence of sexual reproduction and meiotic recombination. This evolutionary paradox is often counterbalanced by invoking their ability to repair environmentally induced genome breakage. By studying the dynamics of DNA damage response in the bdelloid species Adineta vaga, we found that it occurs rapidly in the soma, producing a partially reassembled genome. By contrast, germline DNA repair is delayed to a specific time window of oogenesis during which homologous chromosomes adopt a meiotic-like juxtaposed configuration, resulting in accurate reconstitution of the genome in the offspring. Our finding that a noncanonical meiosis is the mechanism of germline DNA repair in bdelloid rotifers gives previously unidentified insights on their enigmatic long-term evolution.
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Affiliation(s)
- Matthieu Terwagne
- Research Unit in Environmental and Evolutionary Biology (URBE), Laboratory of Evolutionary Genetics and Ecology (LEGE), NAmur Research Institute for Life Sciences (NARILIS), University of Namur (UNamur), Namur 5000, Belgium
- Institute of Biomolecular Science and Technology (LIBST), Université Catholique de Louvain (UCLouvain), Louvain-la-Neuve 1348, Belgium
| | - Emilien Nicolas
- Research Unit in Environmental and Evolutionary Biology (URBE), Laboratory of Evolutionary Genetics and Ecology (LEGE), NAmur Research Institute for Life Sciences (NARILIS), University of Namur (UNamur), Namur 5000, Belgium
- Institute of Biomolecular Science and Technology (LIBST), Université Catholique de Louvain (UCLouvain), Louvain-la-Neuve 1348, Belgium
- Research Unit of Molecular Biology and Evolution (MBE), Université Libre de Bruxelles (ULB), Brussels, 1050, Belgium
| | - Boris Hespeels
- Research Unit in Environmental and Evolutionary Biology (URBE), Laboratory of Evolutionary Genetics and Ecology (LEGE), NAmur Research Institute for Life Sciences (NARILIS), University of Namur (UNamur), Namur 5000, Belgium
- Research Unit in Environmental and Evolutionary Biology (URBE), Institute of Life, Earth and Environment (ILEE), University of Namur (UNamur), Namur 5000, Belgium
| | - Ludovic Herter
- Research Unit in Environmental and Evolutionary Biology (URBE), Laboratory of Evolutionary Genetics and Ecology (LEGE), NAmur Research Institute for Life Sciences (NARILIS), University of Namur (UNamur), Namur 5000, Belgium
| | - Julie Virgo
- Research Unit in Environmental and Evolutionary Biology (URBE), Laboratory of Evolutionary Genetics and Ecology (LEGE), NAmur Research Institute for Life Sciences (NARILIS), University of Namur (UNamur), Namur 5000, Belgium
| | - Catherine Demazy
- Research Unit in Environmental and Evolutionary Biology (URBE), Laboratory of Evolutionary Genetics and Ecology (LEGE), NAmur Research Institute for Life Sciences (NARILIS), University of Namur (UNamur), Namur 5000, Belgium
- Cellular Biology Research Unit (URBC), University of Namur (UNamur), Namur 5000, Belgium
| | - Anne-Catherine Heuskin
- Laboratory of Analysis by Nuclear Reaction (LARN), NAmur Research Institute for Life Sciences (NARILIS), University of Namur (UNamur), Namur 5000, Belgium
| | - Bernard Hallet
- Institute of Biomolecular Science and Technology (LIBST), Université Catholique de Louvain (UCLouvain), Louvain-la-Neuve 1348, Belgium
| | - Karine Van Doninck
- Research Unit in Environmental and Evolutionary Biology (URBE), Laboratory of Evolutionary Genetics and Ecology (LEGE), NAmur Research Institute for Life Sciences (NARILIS), University of Namur (UNamur), Namur 5000, Belgium
- Research Unit of Molecular Biology and Evolution (MBE), Université Libre de Bruxelles (ULB), Brussels, 1050, Belgium
- Research Unit in Environmental and Evolutionary Biology (URBE), Institute of Life, Earth and Environment (ILEE), University of Namur (UNamur), Namur 5000, Belgium
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10
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Evolution of yeast hybrids by aborted meiosis. Curr Opin Genet Dev 2022; 77:101980. [PMID: 36084497 DOI: 10.1016/j.gde.2022.101980] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2022] [Revised: 07/22/2022] [Accepted: 08/01/2022] [Indexed: 01/27/2023]
Abstract
Sterile hybrids are broadly considered evolutionary dead-ends because of their faulty sexual reproduction. While sterility in obligate sexual organisms is a clear constraint in perpetuating the species, some facultative sexual microbes such as yeasts can propagate asexually and maintain genome plasticity. Moreover, incomplete meiotic pathways in yeasts represent alternative routes to the standard meiosis that generates genetic combinations in the population and fuel adaptation. Here, we review how aborting meiosis promotes genome-wide allele shuffling in sterile Saccharomyces hybrids and describe approaches to identify evolved clones in a cell population. We further discuss possible implications of this process in generating phenotypic novelty and report cases of abortive meiosis across yeast species.
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11
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McElroy KE, Bankers L, Soper D, Hehman G, Boore JL, Logsdon JM, Neiman M. Patterns of gene expression in ovaries of sexual vs. asexual lineages of a freshwater snail. Front Ecol Evol 2022. [DOI: 10.3389/fevo.2022.845640] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Why sexual reproduction is so common when asexual reproduction should be much more efficient and less costly remains an open question in evolutionary biology. Comparisons between otherwise similar sexual and asexual taxa allow us to characterize the genetic architecture underlying asexuality, which can, in turn, illuminate how this reproductive mode transition occurred and the mechanisms by which it is maintained or disrupted. Here, we used transcriptome sequencing to compare patterns of ovarian gene expression between actively reproducing obligately sexual and obligately asexual females from multiple lineages of Potamopyrgus antipodarum, a freshwater New Zealand snail characterized by frequent separate transitions to asexuality and coexistence of otherwise similar sexual and asexual lineages. We also used these sequence data to evaluate whether population history accounts for variation in patterns of gene expression. We found that source population was a major source of gene expression variation, and likely more influential than reproductive mode. This outcome for these common garden-raised snails is strikingly similar to earlier results from field-collected snails. While we did not identify a likely set of candidate genes from expression profiles that could plausibly explain how transitions to asexuality occurred, we identified around 1,000 genes with evidence of differential expression between sexual and asexual reproductive modes, and 21 genes that appear to exhibit consistent expression differences between sexuals and asexuals across genetic backgrounds. This second smaller set of genes provides a good starting point for further exploration regarding a potential role in the transition to asexual reproduction. These results mark the first effort to characterize the causes of asexuality in P. antipodarum, demonstrate the apparently high heritability of gene expression patterns in this species, and hint that for P. antipodarum, transitions to asexuality might not necessarily be strongly associated with broad changes in gene expression.
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