1
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Estes S, Dietz ZP, Katju V, Bergthorsson U. Evolutionary codependency: insights into the mitonuclear interaction landscape from experimental and wild Caenorhabditis nematodes. Curr Opin Genet Dev 2023; 81:102081. [PMID: 37421904 DOI: 10.1016/j.gde.2023.102081] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2023] [Revised: 06/07/2023] [Accepted: 06/08/2023] [Indexed: 07/10/2023]
Abstract
Aided by new technologies, the upsurgence of research into mitochondrial genome biology during the past 15 years suggests that we have misunderstood, and perhaps dramatically underestimated, the ongoing biological and evolutionary significance of our long-time symbiotic partner. While we have begun to scratch the surface of several topics, many questions regarding the nature of mutation and selection in the mitochondrial genome, and the nature of its relationship to the nuclear genome, remain unanswered. Although best known for their contributions to studies of developmental and aging biology, Caenorhabditis nematodes are increasingly recognized as excellent model systems to advance understanding in these areas. We review recent discoveries with relevance to mitonuclear coevolution and conflict and offer several fertile areas for future work.
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Affiliation(s)
- Suzanne Estes
- Portland State University, Department of Biology, Portland, OR, USA.
| | - Zachary P Dietz
- Portland State University, Department of Biology, Portland, OR, USA
| | - Vaishali Katju
- Uppsala University, Department of Ecology and Genetics, 752 36 Uppsala, Sweden
| | - Ulfar Bergthorsson
- Uppsala University, Department of Ecology and Genetics, 752 36 Uppsala, Sweden
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2
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Lee J, Willett CS. Frequent Paternal Mitochondrial Inheritance and Rapid Haplotype Frequency Shifts in Copepod Hybrids. J Hered 2022; 113:171-183. [PMID: 35575078 DOI: 10.1093/jhered/esab068] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2021] [Accepted: 10/29/2021] [Indexed: 11/13/2022] Open
Abstract
Mitochondria are assumed to be maternally inherited in most animal species, and this foundational concept has fostered advances in phylogenetics, conservation, and population genetics. Like other animals, mitochondria were thought to be solely maternally inherited in the marine copepod Tigriopus californicus, which has served as a useful model for studying mitonuclear interactions, hybrid breakdown, and environmental tolerance. However, we present PCR, Sanger sequencing, and Illumina Nextera sequencing evidence that extensive paternal mitochondrial DNA (mtDNA) transmission is occurring in inter-population hybrids of T. californicus. PCR on four types of crosses between three populations (total sample size of 376 F1 individuals) with 20% genome-wide mitochondrial divergence showed 2% to 59% of F1 hybrids with both paternal and maternal mtDNA, where low and high paternal leakage values were found in different cross directions of the same population pairs. Sequencing methods further verified nucleotide similarities between F1 mtDNA and paternal mtDNA sequences. Interestingly, the paternal mtDNA in F1s from some crosses inherited haplotypes that were uncommon in the paternal population. Compared to some previous research on paternal leakage, we employed more rigorous methods to rule out contamination and false detection of paternal mtDNA due to non-functional nuclear mitochondrial DNA fragments. Our results raise the potential that other animal systems thought to only inherit maternal mitochondria may also have paternal leakage, which would then affect the interpretation of past and future population genetics or phylogenetic studies that rely on mitochondria as uniparental markers.
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Affiliation(s)
- Jeeyun Lee
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
| | - Christopher S Willett
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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3
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Camus MF, Alexander-Lawrie B, Sharbrough J, Hurst GDD. Inheritance through the cytoplasm. Heredity (Edinb) 2022; 129:31-43. [PMID: 35525886 PMCID: PMC9273588 DOI: 10.1038/s41437-022-00540-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2021] [Revised: 04/19/2022] [Accepted: 04/20/2022] [Indexed: 12/11/2022] Open
Abstract
Most heritable information in eukaryotic cells is encoded in the nuclear genome, with inheritance patterns following classic Mendelian segregation. Genomes residing in the cytoplasm, however, prove to be a peculiar exception to this rule. Cytoplasmic genetic elements are generally maternally inherited, although there are several exceptions where these are paternally, biparentally or doubly-uniparentally inherited. In this review, we examine the diversity and peculiarities of cytoplasmically inherited genomes, and the broad evolutionary consequences that non-Mendelian inheritance brings. We first explore the origins of vertical transmission and uniparental inheritance, before detailing the vast diversity of cytoplasmic inheritance systems across Eukaryota. We then describe the evolution of genomic organisation across lineages, how this process has been shaped by interactions with the nuclear genome and population genetics dynamics. Finally, we discuss how both nuclear and cytoplasmic genomes have evolved to co-inhabit the same host cell via one of the longest symbiotic processes, and all the opportunities for intergenomic conflict that arise due to divergence in inheritance patterns. In sum, we cannot understand the evolution of eukaryotes without understanding hereditary symbiosis.
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Affiliation(s)
- M Florencia Camus
- Department of Genetics, Evolution and Environment, University College London, London, UK.
| | | | - Joel Sharbrough
- Biology Department, New Mexico Institute of Mining and Technology, Socorro, NM, USA
| | - Gregory D D Hurst
- Institute of Infection, Veterinary and Ecological Sciences, University of Liverpool, Liverpool, England
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4
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Klucnika A, Ma H. A battle for transmission: the cooperative and selfish animal mitochondrial genomes. Open Biol 2020; 9:180267. [PMID: 30890027 PMCID: PMC6451365 DOI: 10.1098/rsob.180267] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The mitochondrial genome is an evolutionarily persistent and cooperative component of metazoan cells that contributes to energy production and many other cellular processes. Despite sharing the same host as the nuclear genome, the multi-copy mitochondrial DNA (mtDNA) follows very different rules of replication and transmission, which translate into differences in the patterns of selection. On one hand, mtDNA is dependent on the host for its transmission, so selections would favour genomes that boost organismal fitness. On the other hand, genetic heterogeneity within an individual allows different mitochondrial genomes to compete for transmission. This intra-organismal competition could select for the best replicator, which does not necessarily give the fittest organisms, resulting in mito-nuclear conflict. In this review, we discuss the recent advances in our understanding of the mechanisms and opposing forces governing mtDNA transmission and selection in bilaterians, and what the implications of these are for mtDNA evolution and mitochondrial replacement therapy.
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Affiliation(s)
- Anna Klucnika
- 1 Wellcome Trust/Cancer Research UK Gurdon Institute , Tennis Court Road, Cambridge CB2 1QN , UK.,2 Department of Genetics, University of Cambridge , Downing Street, Cambridge CB2 3EH , UK
| | - Hansong Ma
- 1 Wellcome Trust/Cancer Research UK Gurdon Institute , Tennis Court Road, Cambridge CB2 1QN , UK.,2 Department of Genetics, University of Cambridge , Downing Street, Cambridge CB2 3EH , UK
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5
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Schaack S, Ho EKH, Macrae F. Disentangling the intertwined roles of mutation, selection and drift in the mitochondrial genome. Philos Trans R Soc Lond B Biol Sci 2020; 375:20190173. [PMID: 31787045 PMCID: PMC6939366 DOI: 10.1098/rstb.2019.0173] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/16/2019] [Indexed: 12/31/2022] Open
Abstract
Understanding and quantifying the rates of change in the mitochondrial genome is a major component of many areas of biological inquiry, from phylogenetics to human health. A critical parameter in understanding rates of change is estimating the mitochondrial mutation rate (mtDNA MR). Although the first direct estimates of mtDNA MRs were reported almost 20 years ago, the number of estimates has not grown markedly since that time. This is largely owing to the challenges associated with time- and labour-intensive mutation accumulation (MA) experiments. But even MA experiments do not solve a major problem with estimating mtDNA MRs-the challenge of disentangling the role of mutation from other evolutionary forces acting within the cell. Now that it is widely understood that any newly generated mutant allele in the mitochondria will initially be at very low frequency (1/N, where N is the number of mtDNA molecules in the cell), the importance of understanding the effective population size (Ne) of the mtDNA and the size of genetic bottlenecks during gametogenesis and development has come into the spotlight. In addition to these factors regulating the role of genetic drift, advances in our understanding of mitochondrial replication and turnover allow us to more easily envision how natural selection within the cell might favour or purge mutations in multi-copy organellar genomes. Here, we review the unique features of the mitochondrial genome that pose a challenge for accurate MR estimation and discuss ways to overcome those challenges. Estimates of mtDNA MRs remain one of the most widely used parameters in biology, thus accurate quantification and a deeper understanding of how and why they may vary within and between individuals, populations and species is an important goal. This article is part of the theme issue 'Linking the mitochondrial genotype to phenotype: a complex endeavour'.
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Affiliation(s)
- Sarah Schaack
- Department of Biology, Reed College, Portland, OR 97202, USA
| | - Eddie K H Ho
- Department of Biology, Reed College, Portland, OR 97202, USA
| | - Fenner Macrae
- Department of Biology, Reed College, Portland, OR 97202, USA
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6
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Stegeman GW, Baird SE, Ryu WS, Cutter AD. Genetically Distinct Behavioral Modules Underlie Natural Variation in Thermal Performance Curves. G3 (BETHESDA, MD.) 2019; 9:2135-2151. [PMID: 31048400 PMCID: PMC6643873 DOI: 10.1534/g3.119.400043] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Accepted: 04/30/2019] [Indexed: 01/01/2023]
Abstract
Thermal reaction norms pervade organismal traits as stereotyped responses to temperature, a fundamental environmental input into sensory and physiological systems. Locomotory behavior represents an especially plastic read-out of animal response, with its dynamic dependence on environmental stimuli presenting a challenge for analysis and for understanding the genomic architecture of heritable variation. Here we characterize behavioral reaction norms as thermal performance curves for the nematode Caenorhabditis briggsae, using a collection of 23 wild isolate genotypes and 153 recombinant inbred lines to quantify the extent of genetic and plastic variation in locomotory behavior to temperature changes. By reducing the dimensionality of the multivariate phenotypic response with a function-valued trait framework, we identified genetically distinct behavioral modules that contribute to the heritable variation in the emergent overall behavioral thermal performance curve. Quantitative trait locus mapping isolated regions on Chromosome II associated with locomotory activity at benign temperatures and Chromosome V loci related to distinct aspects of sensitivity to high temperatures, with each quantitative trait locus explaining up to 28% of trait variation. These findings highlight how behavioral responses to environmental inputs as thermal reaction norms can evolve through independent changes to genetically distinct modular components of such complex phenotypes.
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Affiliation(s)
| | - Scott E Baird
- Department of Biology, Wright State University, Dayton, Ohio, 45435
| | - William S Ryu
- Department of Physics, University of Toronto
- Donnelly Centre, University of Toronto, Toronto, Ontario M5S3B2, Canada
| | - Asher D Cutter
- Department of Ecology and Evolutionary Biology, University of Toronto
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7
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Li R, Ren X, Bi Y, Ding Q, Ho VWS, Zhao Z. Comparative mitochondrial genomics reveals a possible role of a recent duplication of NADH dehydrogenase subunit 5 in gene regulation. DNA Res 2018; 25:577-586. [PMID: 30085012 PMCID: PMC6289777 DOI: 10.1093/dnares/dsy026] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Accepted: 07/22/2018] [Indexed: 12/17/2022] Open
Abstract
Mitochondrial genome (mtDNA) carries not only well-conserved protein coding, tRNA and rRNA genes, but also highly variable non-coding regions (NCRs). However, the NCRs show poor conservation across species, making their function and evolution elusive. Identification and functional characterization of NCRs across species would be critical for addressing these questions. To this end, we devised a computational pipeline and performed de novo assembly and annotation of mtDNA from 19 Caenorhabditis species using next-generation sequencing (NGS) data. The mtDNAs for 14 out of the 19 species are reported for the first time. Comparison of the 19 genomes reveals species-specific sampling of partial displacement-loop (D-loop) sequence as a novel NCR inserted into a unique tRNA cluster, suggesting an important role of the D-loop and the tRNA cluster in shaping NCR evolution. Intriguingly, RNA-Seq analysis suggests that a novel NCR resulting from a recent duplication of NADH dehydrogenase subunit 5 (ND5) could be utilized as a 3' UTR for up-regulation of its upstream gene. The expression analysis shows a species- and sex-specific expression of mitochondrial genes encoded by mtDNA and nucleus, respectively. Our analyses provide important insights into the function and evolution of mitochondrial NCRs and pave the way for further studying the function and evolution of mitochondrial genome.
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Affiliation(s)
- Runsheng Li
- Department of Biology, Hong Kong Baptist University, Hong Kong, China
| | - Xiaoliang Ren
- Department of Biology, Hong Kong Baptist University, Hong Kong, China
| | - Yu Bi
- Department of Biology, Hong Kong Baptist University, Hong Kong, China
| | - Qiutao Ding
- Department of Biology, Hong Kong Baptist University, Hong Kong, China
| | - Vincy Wing Sze Ho
- Department of Biology, Hong Kong Baptist University, Hong Kong, China
| | - Zhongying Zhao
- Department of Biology, Hong Kong Baptist University, Hong Kong, China
- State Key Laboratory of Environmental and Biological Analysis, Hong Kong Baptist University, Hong Kong, China
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8
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Palozzi JM, Jeedigunta SP, Hurd TR. Mitochondrial DNA Purifying Selection in Mammals and Invertebrates. J Mol Biol 2018; 430:4834-4848. [DOI: 10.1016/j.jmb.2018.10.019] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2018] [Revised: 10/20/2018] [Accepted: 10/25/2018] [Indexed: 01/19/2023]
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9
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Cutter AD. X exceptionalism in Caenorhabditis speciation. Mol Ecol 2017; 27:3925-3934. [PMID: 29134711 DOI: 10.1111/mec.14423] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Revised: 11/06/2017] [Accepted: 11/07/2017] [Indexed: 12/13/2022]
Abstract
Speciation genetics research in diverse organisms shows the X-chromosome to be exceptional in how it contributes to "rules" of speciation. Until recently, however, the nematode phylum has been nearly silent on this issue, despite the model organism Caenorhabditis elegans having touched most other topics in biology. Studies of speciation with Caenorhabditis accelerated with the recent discovery of species pairs showing partial interfertility. The resulting genetic analyses of reproductive isolation in nematodes demonstrate key roles for the X-chromosome in hybrid male sterility and inviability, opening up new understanding of the genetic causes of Haldane's rule, Darwin's corollary to Haldane's rule, and enabling tests of the large-X effect hypothesis. Studies to date implicate improper chromatin regulation of the X-chromosome by small RNA pathways as integral to hybrid male dysfunction. Sexual transitions in reproductive mode to self-fertilizing hermaphroditism inject distinctive molecular evolutionary features into the speciation process for some species. Caenorhabditis also provides unique opportunities for analysis in a system with XO sex determination that lacks a Y-chromosome, sex chromosome-dependent sperm competition differences and mechanisms of gametic isolation, exceptional accessibility to the development process and rapid experimental evolution. As genetic analysis of reproductive isolation matures with investigation of multiple pairs of Caenorhabditis species and new species discovery, nematodes will provide a powerful complement to more established study organisms for deciphering the genetic basis of and rules to speciation.
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Affiliation(s)
- Asher D Cutter
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, ON, Canada
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10
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Jaleta TG, Zhou S, Bemm FM, Schär F, Khieu V, Muth S, Odermatt P, Lok JB, Streit A. Different but overlapping populations of Strongyloides stercoralis in dogs and humans-Dogs as a possible source for zoonotic strongyloidiasis. PLoS Negl Trop Dis 2017; 11:e0005752. [PMID: 28793306 PMCID: PMC5565190 DOI: 10.1371/journal.pntd.0005752] [Citation(s) in RCA: 99] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2017] [Revised: 08/21/2017] [Accepted: 06/26/2017] [Indexed: 01/10/2023] Open
Abstract
Strongyloidiasis is a much-neglected soil born helminthiasis caused by the nematode Strongyloides stercoralis. Human derived S. stercoralis can be maintained in dogs in the laboratory and this parasite has been reported to also occur in dogs in the wild. Some authors have considered strongyloidiasis a zoonotic disease while others have argued that the two hosts carry host specialized populations of S. stercoralis and that dogs play a minor role, if any, as a reservoir for zoonotic S. stercoralis infections of humans. We isolated S. stercoralis from humans and their dogs in rural villages in northern Cambodia, a region with a high incidence of strongyloidiasis, and compared the worms derived from these two host species using nuclear and mitochondrial DNA sequence polymorphisms. We found that in dogs there exist two populations of S. stercoralis, which are clearly separated from each other genetically based on the nuclear 18S rDNA, the mitochondrial cox1 locus and whole genome sequence. One population, to which the majority of the worms belong, appears to be restricted to dogs. The other population is indistinguishable from the population of S. stercoralis isolated from humans. Consistent with earlier studies, we found multiple sequence variants of the hypervariable region I of the 18 S rDNA in S. stercoralis from humans. However, comparison of mitochondrial sequences and whole genome analysis suggest that these different 18S variants do not represent multiple genetically isolated subpopulations among the worms isolated from humans. We also investigated the mode of reproduction of the free-living generations of laboratory and wild isolates of S. stercoralis. Contrary to earlier literature on S. stercoralis but similar to other species of Strongyloides, we found clear evidence of sexual reproduction. Overall, our results show that dogs carry two populations, possibly different species of Strongyloides. One population appears to be dog specific but the other one is shared with humans. This argues for the strong potential of dogs as reservoirs for zoonotic transmission of S. stercoralis to humans and suggests that in order to reduce the exposure of humans to infective S. stercoralis larvae, dogs should be treated for the infection along with their owners.
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MESH Headings
- Animals
- Cambodia/epidemiology
- Cluster Analysis
- DNA, Helminth/chemistry
- DNA, Helminth/genetics
- DNA, Mitochondrial/chemistry
- DNA, Mitochondrial/genetics
- DNA, Ribosomal/chemistry
- DNA, Ribosomal/genetics
- Disease Reservoirs
- Dog Diseases/epidemiology
- Dog Diseases/parasitology
- Dog Diseases/transmission
- Dogs
- Electron Transport Complex IV/genetics
- Genotype
- Humans
- Molecular Epidemiology
- Phylogeny
- Polymorphism, Genetic
- RNA, Ribosomal, 18S/genetics
- Rural Population
- Sequence Analysis, DNA
- Strongyloides stercoralis/classification
- Strongyloides stercoralis/genetics
- Strongyloides stercoralis/isolation & purification
- Strongyloidiasis/epidemiology
- Strongyloidiasis/parasitology
- Strongyloidiasis/transmission
- Strongyloidiasis/veterinary
- Zoonoses/epidemiology
- Zoonoses/parasitology
- Zoonoses/transmission
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Affiliation(s)
- Tegegn G. Jaleta
- Department of Evolutionary Biology, Max-Planck-Institute for Developmental Biology, Tübingen, Germany
- Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Siyu Zhou
- Department of Evolutionary Biology, Max-Planck-Institute for Developmental Biology, Tübingen, Germany
| | - Felix M. Bemm
- Department of Molecular Biology, Max-Planck-Institute for Developmental Biology, Tübingen, Germany
| | - Fabian Schär
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland
- University of Basel, Basel, Switzerland
| | - Virak Khieu
- National Center for Parasitology, Entomology and Malaria Control, Ministry of Health, Phnom Penh, Cambodia
| | - Sinuon Muth
- National Center for Parasitology, Entomology and Malaria Control, Ministry of Health, Phnom Penh, Cambodia
| | - Peter Odermatt
- Department of Epidemiology and Public Health, Swiss Tropical and Public Health Institute, Basel, Switzerland
- University of Basel, Basel, Switzerland
| | - James B. Lok
- Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Adrian Streit
- Department of Evolutionary Biology, Max-Planck-Institute for Developmental Biology, Tübingen, Germany
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Ancell H, Pires-daSilva A. Sex-specific lifespan and its evolution in nematodes. Semin Cell Dev Biol 2017; 70:122-129. [PMID: 28554570 DOI: 10.1016/j.semcdb.2017.05.012] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Revised: 05/03/2017] [Accepted: 05/18/2017] [Indexed: 12/22/2022]
Abstract
Differences between sexes of the same species in lifespan and aging rate are widespread. While the proximal and evolutionary causes of aging are well researched, the factors that contribute to sex differences in these traits have been less studied. The striking diversity of nematodes provides ample opportunity to study variation in sex-specific lifespan patterns associated with shifts in life history and mating strategy. Although the plasticity of these sex differences will make it challenging to generalize from invertebrate to vertebrate systems, studies in nematodes have enabled empirical evaluation of predictions regarding the evolution of lifespan. These studies have highlighted how natural and sexual selection can generate divergent patterns of lifespan if the sexes are subject to different rates or sources of mortality, or if trade-offs between complex traits and longevity are resolved differently in each sex. Here, we integrate evidence derived mainly from nematodes that addresses the molecular and evolutionary basis of sex-specific aging and lifespan. Ultimately, we hope to generate a clearer picture of current knowledge in this area, and also highlight the limitations of our understanding.
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Affiliation(s)
- Henry Ancell
- School of Life Sciences, University of Warwick, Coventry, CV4 7AL, UK
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12
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Cytoplasmic-Nuclear Incompatibility Between Wild Isolates of Caenorhabditis nouraguensis. G3-GENES GENOMES GENETICS 2017; 7:823-834. [PMID: 28064190 PMCID: PMC5345712 DOI: 10.1534/g3.116.037101] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
How species arise is a fundamental question in biology. Species can be defined as populations of interbreeding individuals that are reproductively isolated from other such populations. Therefore, understanding how reproductive barriers evolve between populations is essential for understanding the process of speciation. Hybrid incompatibility (for example, hybrid sterility or lethality) is a common and strong reproductive barrier in nature. Here we report a lethal incompatibility between two wild isolates of the nematode Caenorhabditis nouraguensis Hybrid inviability results from the incompatibility between a maternally inherited cytoplasmic factor from each strain and a recessive nuclear locus from the other. We have excluded the possibility that maternally inherited endosymbiotic bacteria cause the incompatibility by treating both strains with tetracycline and show that hybrid death is unaffected. Furthermore, cytoplasmic-nuclear incompatibility commonly occurs between other wild isolates, indicating that this is a significant reproductive barrier within C. nouraguensis We hypothesize that the maternally inherited cytoplasmic factor is the mitochondrial genome and that mitochondrial dysfunction underlies hybrid death. This system has the potential to shed light on the dynamics of divergent mitochondrial-nuclear coevolution and its role in promoting speciation.
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