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Tower J. Selectively advantageous instability in biotic and pre-biotic systems and implications for evolution and aging. FRONTIERS IN AGING 2024; 5:1376060. [PMID: 38818026 PMCID: PMC11137231 DOI: 10.3389/fragi.2024.1376060] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/24/2024] [Accepted: 04/15/2024] [Indexed: 06/01/2024]
Abstract
Rules of biology typically involve conservation of resources. For example, common patterns such as hexagons and logarithmic spirals require minimal materials, and scaling laws involve conservation of energy. Here a relationship with the opposite theme is discussed, which is the selectively advantageous instability (SAI) of one or more components of a replicating system, such as the cell. By increasing the complexity of the system, SAI can have benefits in addition to the generation of energy or the mobilization of building blocks. SAI involves a potential cost to the replicating system for the materials and/or energy required to create the unstable component, and in some cases, the energy required for its active degradation. SAI is well-studied in cells. Short-lived transcription and signaling factors enable a rapid response to a changing environment, and turnover is critical for replacement of damaged macromolecules. The minimal gene set for a viable cell includes proteases and a nuclease, suggesting SAI is essential for life. SAI promotes genetic diversity in several ways. Toxin/antitoxin systems promote maintenance of genes, and SAI of mitochondria facilitates uniparental transmission. By creating two distinct states, subject to different selective pressures, SAI can maintain genetic diversity. SAI of components of synthetic replicators favors replicator cycling, promoting emergence of replicators with increased complexity. Both classical and recent computer modeling of replicators reveals SAI. SAI may be involved at additional levels of biological organization. In summary, SAI promotes replicator genetic diversity and reproductive fitness, and may promote aging through loss of resources and maintenance of deleterious alleles.
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Affiliation(s)
- John Tower
- Molecular and Computational Biology Section, Department of Biological Sciences, University of Southern California, Los Angeles, CA, United States
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2
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Dowling DK, Wolff JN. Evolutionary genetics of the mitochondrial genome: insights from Drosophila. Genetics 2023; 224:iyad036. [PMID: 37171259 PMCID: PMC10324950 DOI: 10.1093/genetics/iyad036] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2022] [Accepted: 02/05/2023] [Indexed: 05/13/2023] Open
Abstract
Mitochondria are key to energy conversion in virtually all eukaryotes. Intriguingly, despite billions of years of evolution inside the eukaryote, mitochondria have retained their own small set of genes involved in the regulation of oxidative phosphorylation (OXPHOS) and protein translation. Although there was a long-standing assumption that the genetic variation found within the mitochondria would be selectively neutral, research over the past 3 decades has challenged this assumption. This research has provided novel insight into the genetic and evolutionary forces that shape mitochondrial evolution and broader implications for evolutionary ecological processes. Many of the seminal studies in this field, from the inception of the research field to current studies, have been conducted using Drosophila flies, thus establishing the species as a model system for studies in mitochondrial evolutionary biology. In this review, we comprehensively review these studies, from those focusing on genetic processes shaping evolution within the mitochondrial genome, to those examining the evolutionary implications of interactions between genes spanning mitochondrial and nuclear genomes, and to those investigating the dynamics of mitochondrial heteroplasmy. We synthesize the contribution of these studies to shaping our understanding of the evolutionary and ecological implications of mitochondrial genetic variation.
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Affiliation(s)
- Damian K Dowling
- School of Biological Sciences, Monash University, Melbourne, Victoria 3800, Australia
| | - Jonci N Wolff
- School of Biological Sciences, Monash University, Melbourne, Victoria 3800, Australia
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3
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The Mitochondrial Genome of a Freshwater Pelagic Amphipod Macrohectopus branickii Is among the Longest in Metazoa. Genes (Basel) 2021; 12:genes12122030. [PMID: 34946978 PMCID: PMC8700879 DOI: 10.3390/genes12122030] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2021] [Revised: 11/30/2021] [Accepted: 12/06/2021] [Indexed: 12/29/2022] Open
Abstract
There are more than 350 species of amphipods (Crustacea) in Lake Baikal, which have emerged predominantly through the course of endemic radiation. This group represents a remarkable model for studying various aspects of evolution, one of which is the evolution of mitochondrial (mt) genome architectures. We sequenced and assembled the mt genome of a pelagic Baikalian amphipod species Macrohectopus branickii. The mt genome is revealed to have an extraordinary length (42,256 bp), deviating significantly from the genomes of other amphipod species and the majority of animals. The mt genome of M. branickii has a unique gene order within amphipods, duplications of the four tRNA genes and Cox2, and a long non-coding region, that makes up about two thirds of the genome’s size. The extension of the mt genome was most likely caused by multiple duplications and inversions of regions harboring ribosomal RNA genes. In this study, we analyzed the patterns of mt genome length changes in amphipods and other animal phyla. Through a statistical analysis, we demonstrated that the variability in the mt genome length may be a characteristic of certain phyla and is primarily conferred by expansions of non-coding regions.
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Ghiselli F, Iannello M, Piccinini G, Milani L. Bivalve molluscs as model systems for studying mitochondrial biology. Integr Comp Biol 2021; 61:1699-1714. [PMID: 33944910 DOI: 10.1093/icb/icab057] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
The class Bivalvia is a highly successful and ancient taxon including ∼25,000 living species. During their long evolutionary history bivalves adapted to a wide range of physicochemical conditions, habitats, biological interactions, and feeding habits. Bivalves can have strikingly different size, and despite their apparently simple body plan, they evolved very different shell shapes, and complex anatomic structures. One of the most striking features of this class of animals is their peculiar mitochondrial biology: some bivalves have facultatively anaerobic mitochondria that allow them to survive prolonged periods of anoxia/hypoxia. Moreover, more than 100 species have now been reported showing the only known evolutionarily stable exception to the strictly maternal inheritance of mitochondria in animals, named doubly uniparental inheritance. Mitochondrial activity is fundamental to eukaryotic life, and thanks to their diversity and uncommon features, bivalves represent a great model system to expand our knowledge about mitochondrial biology, so far limited to a few species. We highlight recent works studying mitochondrial biology in bivalves at either genomic or physiological level. A link between these two approaches is still missing, and we believe that an integrated approach and collaborative relationships are the only possible ways to be successful in such endeavour.
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Affiliation(s)
- Fabrizio Ghiselli
- Department of Biological, Geological, and Environmental Sciences, University of Bologna, Italy
| | - Mariangela Iannello
- Department of Biological, Geological, and Environmental Sciences, University of Bologna, Italy
| | - Giovanni Piccinini
- Department of Biological, Geological, and Environmental Sciences, University of Bologna, Italy
| | - Liliana Milani
- Department of Biological, Geological, and Environmental Sciences, University of Bologna, Italy
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5
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Qu T, Calabrese P, Singhavi P, Tower J. Incorporating antagonistic pleiotropy into models for molecular replicators. Biosystems 2020; 201:104333. [PMID: 33359635 DOI: 10.1016/j.biosystems.2020.104333] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2020] [Revised: 12/17/2020] [Accepted: 12/17/2020] [Indexed: 11/15/2022]
Abstract
In modern cells, chromosomal genes composed of DNA encode multi-subunit protein/RNA complexes that catalyze the replication of the chromosome and cell. One prevailing theory for the origin of life posits an early stage involving self-replicating macromolecules called replicators, which can be considered genes capable of self-replication. One prevailing theory for the genetics of aging in humans and other organisms is antagonistic pleiotropy, which posits that a gene can be beneficial in one context, and detrimental in another context. We previously reported that the conceptual simplicity of molecular replicators facilitates the generation of two simple models involving antagonistic pleiotropy. Here a third model is proposed, and each of the three models is presented with improved definition of the time variable. Computer simulations were used to calculate the proliferation of a hypothetical two-subunit replicator (AB), when one of the two subunits (B) exhibits antagonistic pleiotropy, leading to an advantage for B to be unstable. In model 1, instability of B yields free A subunits, which in turn stimulate the activity of other AB replicators. In model 2, B is lost and sometimes replaced by a more active mutant form, B'. In model 3, B becomes damaged and loses activity, and its instability allows it to be replaced by a new B. For each model, conditions were identified where instability of B was detrimental, and where instability of B was beneficial. The results are consistent with the hypothesis that antagonistic pleiotropy can promote molecular instability and system complexity, and provide further support for a model linking aging and evolution.
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Affiliation(s)
- Tianjiao Qu
- Molecular and Computational Biology Section, Department of Biological Sciences, University of Southern California, Los Angeles, CA, 90089, USA
| | - Peter Calabrese
- Quantitative and Computational Biology Section, Department of Biological Sciences, University of Southern California, Los Angeles, CA, 90089, USA
| | - Pratik Singhavi
- Molecular and Computational Biology Section, Department of Biological Sciences, University of Southern California, Los Angeles, CA, 90089, USA
| | - John Tower
- Molecular and Computational Biology Section, Department of Biological Sciences, University of Southern California, Los Angeles, CA, 90089, USA.
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6
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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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Bottleneck and selection in the germline and maternal age influence transmission of mitochondrial DNA in human pedigrees. Proc Natl Acad Sci U S A 2019; 116:25172-25178. [PMID: 31757848 PMCID: PMC6911200 DOI: 10.1073/pnas.1906331116] [Citation(s) in RCA: 58] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Heteroplasmy-the presence of multiple mitochondrial DNA (mtDNA) haplotypes in an individual-can lead to numerous mitochondrial diseases. The presentation of such diseases depends on the frequency of the heteroplasmic variant in tissues, which, in turn, depends on the dynamics of mtDNA transmissions during germline and somatic development. Thus, understanding and predicting these dynamics between generations and within individuals is medically relevant. Here, we study patterns of heteroplasmy in 2 tissues from each of 345 humans in 96 multigenerational families, each with, at least, 2 siblings (a total of 249 mother-child transmissions). This experimental design has allowed us to estimate the timing of mtDNA mutations, drift, and selection with unprecedented precision. Our results are remarkably concordant between 2 complementary population-genetic approaches. We find evidence for a severe germline bottleneck (7-10 mtDNA segregating units) that occurs independently in different oocyte lineages from the same mother, while somatic bottlenecks are less severe. We demonstrate that divergence between mother and offspring increases with the mother's age at childbirth, likely due to continued drift of heteroplasmy frequencies in oocytes under meiotic arrest. We show that this period is also accompanied by mutation accumulation leading to more de novo mutations in children born to older mothers. We show that heteroplasmic variants at intermediate frequencies can segregate for many generations in the human population, despite the strong germline bottleneck. We show that selection acts during germline development to keep the frequency of putatively deleterious variants from rising. Our findings have important applications for clinical genetics and genetic counseling.
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Abstract
Mitochondria, a nearly ubiquitous feature of eukaryotes, are derived from an ancient symbiosis. Despite billions of years of cooperative coevolution - in what is arguably the most important mutualism in the history of life - the persistence of mitochondrial genomes also creates conditions for genetic conflict with the nucleus. Because mitochondrial genomes are present in numerous copies per cell, they are subject to both within- and among-organism levels of selection. Accordingly, 'selfish' genotypes that increase their own proliferation can rise to high frequencies even if they decrease organismal fitness. It has been argued that uniparental (often maternal) inheritance of cytoplasmic genomes evolved to curtail such selfish replication by minimizing within-individual variation and, hence, within-individual selection. However, uniparental inheritance creates conditions for cytonuclear conflict over sex determination and sex ratio, as well as conditions for sexual antagonism when mitochondrial variants increase transmission by enhancing maternal fitness but have the side-effect of being harmful to males (i.e., 'mother's curse'). Here, we review recent advances in understanding selfish replication and sexual antagonism in the evolution of mitochondrial genomes and the mechanisms that suppress selfish interactions, drawing parallels and contrasts with other organelles (plastids) and bacterial endosymbionts that arose more recently. Although cytonuclear conflict is widespread across eukaryotes, it can be cryptic due to nuclear suppression, highly variable, and lineage-specific, reflecting the diverse biology of eukaryotes and the varying architectures of their cytoplasmic genomes.
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Affiliation(s)
- Justin C Havird
- Department of Integrative Biology, The University of Texas, Austin, TX 78712, USA.
| | - Evan S Forsythe
- Department of Biology, Colorado State University, Fort Collins, CO 80523, USA
| | - Alissa M Williams
- Department of Biology, Colorado State University, Fort Collins, CO 80523, USA
| | - John H Werren
- Department of Biology, University of Rochester, Rochester, NY 14627, USA
| | - Damian K Dowling
- School of Biological Sciences, Monash University, Clayton, Victoria 3800, Australia
| | - Daniel B Sloan
- Department of Biology, Colorado State University, Fort Collins, CO 80523, USA
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9
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Ren Q, Zhang F, Xu H. Proliferation Cycle Causes Age Dependent Mitochondrial Deficiencies and Contributes to the Aging of Stem Cells. Genes (Basel) 2017; 8:genes8120397. [PMID: 29257059 PMCID: PMC5748715 DOI: 10.3390/genes8120397] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Revised: 11/17/2017] [Accepted: 12/14/2017] [Indexed: 12/15/2022] Open
Abstract
In addition to chronological aging, stem cells are also subject to proliferative aging during the adult life span. However, the consequences of proliferative cycle and their contributions to stem cells aging have not been well investigated. Using Drosophila female germ line stem cells as a model, we found that the replication cycle leads to the age dependent decline of female fecundity, and is a major factor causing developmental abnormalities in the progeny of old females. The proliferative aging does not cause telomere shortening, but causes an accumulation of mitochondrial DNA (mtDNA) mutations or rearrangements at the control region. We propose that damaging mutations on mtDNA caused by accumulation of proliferation cycles in aged stem cells may disrupt mitochondrial respiration chain and impair mtDNA replication and represent a conserved mechanism underlying stem cell aging.
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Affiliation(s)
- Qiuting Ren
- Laboratory of Molecular Genetics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Fan Zhang
- Laboratory of Molecular Genetics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Hong Xu
- Laboratory of Molecular Genetics, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA.
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10
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Konrad A, Thompson O, Waterston RH, Moerman DG, Keightley PD, Bergthorsson U, Katju V. Mitochondrial Mutation Rate, Spectrum and Heteroplasmy in Caenorhabditis elegans Spontaneous Mutation Accumulation Lines of Differing Population Size. Mol Biol Evol 2017; 34:1319-1334. [PMID: 28087770 DOI: 10.1093/molbev/msx051] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Mitochondrial genomes of metazoans, given their elevated rates of evolution, have served as pivotal markers for phylogeographic studies and recent phylogenetic events. In order to determine the dynamics of spontaneous mitochondrial mutations in small populations in the absence and presence of selection, we evolved mutation accumulation (MA) lines of Caenorhabditis elegans in parallel over 409 consecutive generations at three varying population sizes of N = 1, 10, and 100 hermaphrodites. The N =1 populations should have a minimal influence of natural selection to provide the spontaneous mutation rate and the expected rate of neutral evolution, whereas larger population sizes should experience increasing intensity of selection. New mutations were identified by Illumina paired-end sequencing of 86 mtDNA genomes across 35 experimental lines and compared with published genomes of natural isolates. The spontaneous mitochondrial mutation rate was estimated at 1.05 × 10-7/site/generation. A strong G/C→A/T mutational bias was observed in both the MA lines and the natural isolates. This suggests that the low G + C content at synonymous sites is the product of mutation bias rather than selection as previously proposed. The mitochondrial effective population size per worm generation was estimated to be 62. Although it was previously concluded that heteroplasmy was rare in C. elegans, the vast majority of mutations in this study were heteroplasmic despite an experimental regime exceeding 400 generations. The frequencies of frameshift and nonsynonymous mutations were negatively correlated with population size, which suggests their deleterious effects on fitness and a potent role for selection in their eradication.
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Affiliation(s)
- Anke Konrad
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, TX
| | - Owen Thompson
- Department of Genome Sciences, University of Washington, Seattle, WA
| | | | - Donald G Moerman
- Department of Zoology and Michael Smith Laboratories, University of British Columbia, Vancouver, BC, Canada
| | - Peter D Keightley
- Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, United Kingdom
| | - Ulfar Bergthorsson
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, TX
| | - Vaishali Katju
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, TX
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Ma H, O'Farrell PH. Selfish drive can trump function when animal mitochondrial genomes compete. Nat Genet 2016; 48:798-802. [PMID: 27270106 PMCID: PMC4925267 DOI: 10.1038/ng.3587] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2015] [Accepted: 05/13/2016] [Indexed: 12/11/2022]
Abstract
Mitochondrial genomes compete for transmission from mother to progeny. We explored this competition by introducing a second genome into Drosophila melanogaster to follow transmission. Competitions between closely related genomes favored those functional in electron transport, resulting in a host-beneficial purifying selection. In contrast, matchups between distantly related genomes often favored those with negligible, negative or lethal consequences, indicating selfish selection. Exhibiting powerful selfish selection, a genome carrying a detrimental mutation displaced a complementing genome, leading to population death after several generations. In a different pairing, opposing selfish and purifying selection counterbalanced to give stable transmission of two genomes. Sequencing of recombinant mitochondrial genomes showed that the noncoding region, containing origins of replication, governs selfish transmission. Uniparental inheritance prevents encounters between distantly related genomes. Nonetheless, in each maternal lineage, constant competition among sibling genomes selects for super-replicators. We suggest that this relentless competition drives positive selection, promoting change in the sequences influencing transmission.
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Affiliation(s)
- Hansong Ma
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, California, USA
| | - Patrick H O'Farrell
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, California, USA
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12
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Govindaraju DR, Annaswamy AM. Application of Smart Infrastructure Systems approach to precision medicine. Appl Transl Genom 2015; 7:40-4. [PMID: 27054084 PMCID: PMC4803774 DOI: 10.1016/j.atg.2015.10.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Accepted: 10/20/2015] [Indexed: 11/17/2022]
Abstract
All biological variation is hierarchically organized dynamic network system of genomic components, organelles, cells, tissues, organs, individuals, families, populations and metapopulations. Individuals are axial in this hierarchy, as they represent antecedent, attendant and anticipated aspects of health, disease, evolution and medical care. Humans show individual specific genetic and clinical features such as complexity, cooperation, resilience, robustness, vulnerability, self-organization, latent and emergent behavior during their development, growth and senescence. Accurate collection, measurement, organization and analyses of individual specific data, embedded at all stratified levels of biological, demographic and cultural diversity - the big data - is necessary to make informed decisions on health, disease and longevity; which is a central theme of precision medicine initiative (PMI). This initiative also calls for the development of novel analytical approaches to handle complex multidimensional data. Here we suggest the application of Smart Infrastructure Systems (SIS) approach to accomplish some of the goals set forth by the PMI on the premise that biological systems and the SIS share many common features. The latter has been successfully employed in managing complex networks of non-linear adaptive controls, commonly encountered in smart engineering systems. We highlight their concordance and discuss the utility of the SIS approach in precision medicine programs.
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Affiliation(s)
- Diddahally R. Govindaraju
- The Institute for Aging Research, The Glenn Center for the Biology of Human Aging, Albert Einstein College of Medicine, Bronx, NY 10461, United States
| | - Anuradha M. Annaswamy
- Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
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Similar Efficacies of Selection Shape Mitochondrial and Nuclear Genes in Both Drosophila melanogaster and Homo sapiens. G3-GENES GENOMES GENETICS 2015; 5:2165-76. [PMID: 26297726 PMCID: PMC4592998 DOI: 10.1534/g3.114.016493] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Deleterious mutations contribute to polymorphism even when selection effectively prevents their fixation. The efficacy of selection in removing deleterious mitochondrial mutations from populations depends on the effective population size (Ne) of the mitochondrial DNA and the degree to which a lack of recombination magnifies the effects of linked selection. Using complete mitochondrial genomes from Drosophila melanogaster and nuclear data available from the same samples, we reexamine the hypothesis that nonrecombining animal mitochondrial DNA harbor an excess of deleterious polymorphisms relative to the nuclear genome. We find no evidence of recombination in the mitochondrial genome, and the much-reduced level of mitochondrial synonymous polymorphism relative to nuclear genes is consistent with a reduction in Ne. Nevertheless, we find that the neutrality index, a measure of the excess of nonsynonymous polymorphism relative to the neutral expectation, is only weakly significantly different between mitochondrial and nuclear loci. This difference is likely the result of the larger proportion of beneficial mutations in X-linked relative to autosomal loci, and we find little to no difference between mitochondrial and autosomal neutrality indices. Reanalysis of published data from Homo sapiens reveals a similar lack of a difference between the two genomes, although previous studies have suggested a strong difference in both species. Thus, despite a smaller Ne, mitochondrial loci of both flies and humans appear to experience similar efficacies of purifying selection as do loci in the recombining nuclear genome.
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Ma H, O'Farrell PH. Selections that isolate recombinant mitochondrial genomes in animals. eLife 2015; 4:e07247. [PMID: 26237110 PMCID: PMC4584245 DOI: 10.7554/elife.07247] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2015] [Accepted: 08/01/2015] [Indexed: 12/11/2022] Open
Abstract
Homologous recombination is widespread and catalyzes evolution. Nonetheless, its existence in animal mitochondrial DNA is questioned. We designed selections for recombination between co-resident mitochondrial genomes in various heteroplasmic Drosophila lines. In four experimental settings, recombinant genomes became the sole or dominant genome in the progeny. Thus, selection uncovers occurrence of homologous recombination in Drosophila mtDNA and documents its functional benefit. Double-strand breaks enhanced recombination in the germline and revealed somatic recombination. When the recombination partner was a diverged Drosophila melanogaster genome or a genome from a different species such as Drosophila yakuba, sequencing revealed long continuous stretches of exchange. In addition, the distribution of sequence polymorphisms in recombinants allowed us to map a selected trait to a particular region in the Drosophila mitochondrial genome. Thus, recombination can be harnessed to dissect function and evolution of mitochondrial genome.
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Affiliation(s)
- Hansong Ma
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States
| | - Patrick H O'Farrell
- Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, United States
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15
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Tower J. Mitochondrial maintenance failure in aging and role of sexual dimorphism. Arch Biochem Biophys 2015; 576:17-31. [PMID: 25447815 PMCID: PMC4409928 DOI: 10.1016/j.abb.2014.10.008] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2014] [Revised: 10/08/2014] [Accepted: 10/18/2014] [Indexed: 12/31/2022]
Abstract
Gene expression changes during aging are partly conserved across species, and suggest that oxidative stress, inflammation and proteotoxicity result from mitochondrial malfunction and abnormal mitochondrial-nuclear signaling. Mitochondrial maintenance failure may result from trade-offs between mitochondrial turnover versus growth and reproduction, sexual antagonistic pleiotropy and genetic conflicts resulting from uni-parental mitochondrial transmission, as well as mitochondrial and nuclear mutations and loss of epigenetic regulation. Aging phenotypes and interventions are often sex-specific, indicating that both male and female sexual differentiation promote mitochondrial failure and aging. Studies in mammals and invertebrates implicate autophagy, apoptosis, AKT, PARP, p53 and FOXO in mediating sex-specific differences in stress resistance and aging. The data support a model where the genes Sxl in Drosophila, sdc-2 in Caenorhabditis elegans, and Xist in mammals regulate mitochondrial maintenance across generations and in aging. Several interventions that increase life span cause a mitochondrial unfolded protein response (UPRmt), and UPRmt is also observed during normal aging, indicating hormesis. The UPRmt may increase life span by stimulating mitochondrial turnover through autophagy, and/or by inhibiting the production of hormones and toxic metabolites. The data suggest that metazoan life span interventions may act through a common hormesis mechanism involving liver UPRmt, mitochondrial maintenance and sexual differentiation.
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Affiliation(s)
- John Tower
- Molecular and Computational Biology Program, Department of Biological Sciences, University of Southern California, Los Angeles, CA 90089-2910, United States.
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Abstract
Since the unexpected discovery that mitochondria contain their own distinct DNA molecules, studies of the mitochondrial DNA (mtDNA) have yielded many surprises. In animals, transmission of the mtDNA genome is explicitly non-Mendelian, with a very high number of genome copies being inherited from the mother after a drastic bottleneck. Recent work has begun to uncover the molecular details of this unusual mode of transmission. Many surprising variations in animal mitochondrial biology are known; however, a series of recent studies have identified a core of evolutionarily conserved mechanisms relating to mtDNA inheritance, e.g., mtDNA bottlenecks during germ cell development, selection against specific mtDNA mutation types during maternal transmission, and targeted destruction of sperm mitochondria. In this review, we outline recent literature on the transmission of mtDNA in animals and highlight the implications for human health and ageing.
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17
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Ju YS, Alexandrov LB, Gerstung M, Martincorena I, Nik-Zainal S, Ramakrishna M, Davies HR, Papaemmanuil E, Gundem G, Shlien A, Bolli N, Behjati S, Tarpey PS, Nangalia J, Massie CE, Butler AP, Teague JW, Vassiliou GS, Green AR, Du MQ, Unnikrishnan A, Pimanda JE, Teh BT, Munshi N, Greaves M, Vyas P, El-Naggar AK, Santarius T, Collins VP, Grundy R, Taylor JA, Hayes DN, Malkin D, Foster CS, Warren AY, Whitaker HC, Brewer D, Eeles R, Cooper C, Neal D, Visakorpi T, Isaacs WB, Bova GS, Flanagan AM, Futreal PA, Lynch AG, Chinnery PF, McDermott U, Stratton MR, Campbell PJ. Origins and functional consequences of somatic mitochondrial DNA mutations in human cancer. eLife 2014; 3:e02935. [PMID: 25271376 PMCID: PMC4371858 DOI: 10.7554/elife.02935] [Citation(s) in RCA: 280] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Accepted: 09/26/2014] [Indexed: 01/04/2023] Open
Abstract
Recent sequencing studies have extensively explored the somatic alterations present in the nuclear genomes of cancers. Although mitochondria control energy metabolism and apoptosis, the origins and impact of cancer-associated mutations in mtDNA are unclear. In this study, we analyzed somatic alterations in mtDNA from 1675 tumors. We identified 1907 somatic substitutions, which exhibited dramatic replicative strand bias, predominantly C > T and A > G on the mitochondrial heavy strand. This strand-asymmetric signature differs from those found in nuclear cancer genomes but matches the inferred germline process shaping primate mtDNA sequence content. A number of mtDNA mutations showed considerable heterogeneity across tumor types. Missense mutations were selectively neutral and often gradually drifted towards homoplasmy over time. In contrast, mutations resulting in protein truncation undergo negative selection and were almost exclusively heteroplasmic. Our findings indicate that the endogenous mutational mechanism has far greater impact than any other external mutagens in mitochondria and is fundamentally linked to mtDNA replication.
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Affiliation(s)
- Young Seok Ju
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Ludmil B Alexandrov
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Moritz Gerstung
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Inigo Martincorena
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Serena Nik-Zainal
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Manasa Ramakrishna
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Helen R Davies
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Elli Papaemmanuil
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Gunes Gundem
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Adam Shlien
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Niccolo Bolli
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Sam Behjati
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Patrick S Tarpey
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Jyoti Nangalia
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
- Cambridge University Hospitals NHS Foundation
Trust, Cambridge, United Kingdom
- Department of Haematology,
University of Cambridge, Cambridge, United
Kingdom
| | - Charles E Massie
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
- Cambridge University Hospitals NHS Foundation
Trust, Cambridge, United Kingdom
- Department of Haematology,
University of Cambridge, Cambridge, United
Kingdom
| | - Adam P Butler
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Jon W Teague
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - George S Vassiliou
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
- Cambridge University Hospitals NHS Foundation
Trust, Cambridge, United Kingdom
- Department of Haematology,
University of Cambridge, Cambridge, United
Kingdom
| | - Anthony R Green
- Cambridge University Hospitals NHS Foundation
Trust, Cambridge, United Kingdom
- Department of Haematology,
University of Cambridge, Cambridge, United
Kingdom
| | - Ming-Qing Du
- Cambridge University Hospitals NHS Foundation
Trust, Cambridge, United Kingdom
| | - Ashwin Unnikrishnan
- Lowy Cancer Research
Centre, University of New South Wales,
Sydney, Australia
| | - John E Pimanda
- Lowy Cancer Research
Centre, University of New South Wales,
Sydney, Australia
| | - Bin Tean Teh
- Laboratory of Cancer
Epigenome, National Cancer Centre,
Singapore, Singapore
- Duke-NUS Graduate Medical School,
Singapore, Singapore
| | - Nikhil Munshi
- Department of Hematologic
Oncology, Dana-Farber Cancer Institute,
Boston, United States
| | - Mel Greaves
- Institute of Cancer Research, Sutton,
London, United Kingdom
| | - Paresh Vyas
- Weatherall Institute for Molecular
Medicine, University of Oxford,
Oxford, United Kingdom
| | - Adel K El-Naggar
- Department of Pathology,
MD Anderson Cancer Center, Houston, United
States
| | - Tom Santarius
- Cambridge University Hospitals NHS Foundation
Trust, Cambridge, United Kingdom
| | - V Peter Collins
- Cambridge University Hospitals NHS Foundation
Trust, Cambridge, United Kingdom
| | - Richard Grundy
- Children's Brain Tumour Research
Centre, University of Nottingham,
Nottingham, United Kingdom
| | - Jack A Taylor
- National Institute of Environmental
Health Sciences, National Institute of
Health, Triangle,
North Carolina, United
States
| | - D Neil Hayes
- Department of Internal
Medicine, University of North Carolina,
Chapel
Hill, United States
| | - David Malkin
- Hospital for Sick
Children, University of Toronto,
Toronto, Canada
| | - Christopher S Foster
- Department of Molecular and Clinical
Cancer Medicine, University of Liverpool,
London, United Kingdom
- HCA Pathology Laboratories,
London, United Kingdom
| | - Anne Y Warren
- Cambridge University Hospitals NHS Foundation
Trust, Cambridge, United Kingdom
| | - Hayley C Whitaker
- Cancer Research UK Cambridge
Institute, University of Cambridge,
Cambridge, United Kingdom
| | - Daniel Brewer
- Institute of Cancer Research, Sutton,
London, United Kingdom
- School of Biological
Sciences, University of East Anglia,
Norwich, United Kingdom
| | - Rosalind Eeles
- Institute of Cancer Research, Sutton,
London, United Kingdom
| | - Colin Cooper
- Institute of Cancer Research, Sutton,
London, United Kingdom
- School of Biological
Sciences, University of East Anglia,
Norwich, United Kingdom
| | - David Neal
- Cancer Research UK Cambridge
Institute, University of Cambridge,
Cambridge, United Kingdom
| | - Tapio Visakorpi
- Institute of Biosciences and Medical
Technology - BioMediTech and Fimlab Laboratories,
University of Tampere and Tampere University Hospital,
Tampere, Finland
| | - William B Isaacs
- Department of Oncology,
Johns Hopkins University, Baltimore, United
States
| | - G Steven Bova
- Institute of Biosciences and Medical
Technology - BioMediTech and Fimlab Laboratories,
University of Tampere and Tampere University Hospital,
Tampere, Finland
| | - Adrienne M Flanagan
- Department of
Histopathology, Royal National Orthopaedic
Hospital, Middlesex, United Kingdom
- University College London Cancer
Institute, University College London,
London, United Kingdom
| | - P Andrew Futreal
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
- Department of Genomic
Medicine, The University of Texas, MD Anderson Cancer
Center, Houston, Texas, United States
| | - Andy G Lynch
- Cancer Research UK Cambridge
Institute, University of Cambridge,
Cambridge, United Kingdom
| | - Patrick F Chinnery
- Wellcome Trust Centre for Mitochondrial
Research, Institute of Genetic Medicine, Newcastle
University, Newcastle-upon-tyne, United
Kingdom
| | - Ultan McDermott
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
- Cambridge University Hospitals NHS Foundation
Trust, Cambridge, United Kingdom
| | - Michael R Stratton
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
| | - Peter J Campbell
- Cancer Genome Project,
Wellcome Trust Sanger Institute,
Hinxton, United Kingdom
- Cambridge University Hospitals NHS Foundation
Trust, Cambridge, United Kingdom
- Department of Haematology,
University of Cambridge, Cambridge, United
Kingdom
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18
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Dokianakis E, Ladoukakis ED. Different degree of paternal mtDNA leakage between male and female progeny in interspecific Drosophila crosses. Ecol Evol 2014; 4:2633-41. [PMID: 25077015 PMCID: PMC4113288 DOI: 10.1002/ece3.1069] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2013] [Revised: 11/15/2013] [Accepted: 11/24/2013] [Indexed: 12/17/2022] Open
Abstract
Maternal transmission of mitochondrial DNA (mtDNA) in animals is thought to prevent the spread of selfish deleterious mtDNA mutations in the population. Various mechanisms have been evolved independently to prevent the entry of sperm mitochondria in the embryo. However, the increasing number of instances of paternal mtDNA leakage suggests that these mechanisms are not very effective. The destruction of sperm mitochondria in mammalian embryos is mediated by nuclear factors. Also, the destruction of paternal mitochondria in intraspecific crosses is more effective than in interspecific ones. These observations have led to the hypothesis that leakage of paternal mtDNA (and consequently mtDNA recombination owing to ensuing heteroplasmy) might be more common in inter- than in intraspecific crosses and that it should increase with phylogenetic distance of hybridizing species. We checked paternal leakage in inter- and intraspecific crosses in Drosophila and found little evidence for this hypothesis. In addition, we have observed a higher level of leakage among male than among female progeny from the same cross. This is the first report of sex-specific leakage of paternal mtDNA. It suggests that paternal mtDNA leakage might not be a stochastic result of an error-prone mechanism, but rather, it may be under complex genetic control.
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Abstract
Natural selection defined by differential survival and reproduction of individuals in populations is influenced by genetic, developmental, and environmental factors operating at every age and stage in human life history: generation of gametes, conception, birth, maturation, reproduction, senescence, and death. Biological systems are built upon a hierarchical organization nesting subcellular organelles, cells, tissues, and organs within individuals, individuals within families, and families within populations, and the latter among other populations. Natural selection often acts simultaneously at more than one level of biological organization and on specific traits, which we define as multilevel selection. Under this model, the individual is a fundamental unit of biological organization and also of selection, imbedded in a larger evolutionary context, just as it is a unit of medical intervention imbedded in larger biological, cultural, and environmental contexts. Here, we view human health and life span as necessary consequences of natural selection, operating at all levels and phases of biological hierarchy in human life history as well as in sociological and environmental milieu. An understanding of the spectrum of opportunities for natural selection will help us develop novel approaches to improving healthy life span through specific and global interventions that simultaneously focus on multiple levels of biological organization. Indeed, many opportunities exist to apply multilevel selection models employed in evolutionary biology and biodemography to improving human health at all hierarchical levels. Multilevel selection perspective provides a rational theoretical foundation for a synthesis of medicine and evolution that could lead to discovering effective predictive, preventive, palliative, potentially curative, and individualized approaches in medicine and in global health programs.
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20
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Dowling DK. Evolutionary perspectives on the links between mitochondrial genotype and disease phenotype. Biochim Biophys Acta Gen Subj 2013; 1840:1393-403. [PMID: 24246955 DOI: 10.1016/j.bbagen.2013.11.013] [Citation(s) in RCA: 77] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2013] [Revised: 10/24/2013] [Accepted: 11/11/2013] [Indexed: 01/09/2023]
Abstract
BACKGROUND Disorders of the mitochondrial respiratory chain are heterogeneous in their symptoms and underlying genetics. Simple links between candidate mutations and expression of disease phenotype typically do not exist. It thus remains unclear how the genetic variation in the mitochondrial genome contributes to the phenotypic expression of complex traits and disease phenotypes. SCOPE OF REVIEW I summarize the basic genetic processes known to underpin mitochondrial disease. I highlight other plausible processes, drawn from the evolutionary biological literature, whose contribution to mitochondrial disease expression remains largely empirically unexplored. I highlight recent advances to the field, and discuss common-ground and -goals shared by researchers across medical and evolutionary domains. MAJOR CONCLUSIONS Mitochondrial genetic variance is linked to phenotypic variance across a variety of traits (e.g. reproductive function, life expectancy) fundamental to the upkeep of good health. Evolutionary theory predicts that mitochondrial genomes are destined to accumulate male-harming (but female-friendly) mutations, and this prediction has received proof-of-principle support. Furthermore, mitochondrial effects on the phenotype are typically manifested via interactions between mitochondrial and nuclear genes. Thus, whether a mitochondrial mutation is pathogenic in effect can depend on the nuclear genotype in which is it expressed. GENERAL SIGNIFICANCE Many disease phenotypes associated with OXPHOS malfunction might be determined by the outcomes of mitochondrial-nuclear interactions, and by the evolutionary forces that historically shaped mitochondrial DNA (mtDNA) sequences. Concepts and results drawn from the evolutionary sciences can have broad, but currently under-utilized, applicability to the medical sciences and provide new insights into understanding the complex genetics of mitochondrial disease. This article is part of a Special Issue entitled Frontiers of Mitochondrial Research.
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Affiliation(s)
- Damian K Dowling
- School of Biological Sciences, Monash University, Clayton 3800, VIC Australia
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21
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Jasmin JN, Zeyl C. RAPID EVOLUTION OF CHEATING MITOCHONDRIAL GENOMES IN SMALL YEAST POPULATIONS. Evolution 2013; 68:269-75. [DOI: 10.1111/evo.12228] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Accepted: 07/30/2013] [Indexed: 01/05/2023]
Affiliation(s)
- Jean-Nicolas Jasmin
- Department of Biology; Wake Forest University; Winston-Salem North Carolina 27109
| | - Clifford Zeyl
- Department of Biology; Wake Forest University; Winston-Salem North Carolina 27109
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22
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Pease JB, Hahn MW. More accurate phylogenies inferred from low-recombination regions in the presence of incomplete lineage sorting. Evolution 2013; 67:2376-84. [PMID: 23888858 DOI: 10.1111/evo.12118] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2012] [Accepted: 03/20/2013] [Indexed: 12/17/2022]
Abstract
When speciation events occur in rapid succession, incomplete lineage sorting (ILS) can cause disagreement among individual gene trees. The probability that ILS affects a given locus is directly related to its effective population size (Ne ), which in turn is proportional to the recombination rate if there is strong selection across the genome. Based on these expectations, we hypothesized that low-recombination regions of the genome, as well as sex chromosomes and nonrecombining chromosomes, should exhibit lower levels of ILS. We tested this hypothesis in phylogenomic datasets from primates, the Drosophila melanogaster clade, and the Drosophila simulans clade. In all three cases, regions of the genome with low or no recombination showed significantly stronger support for the putative species tree, although results from the X chromosome differed among clades. Our results suggest that recurrent selection is acting in these low-recombination regions, such that current levels of diversity also reflect past decreases in the effective population size at these same loci. The results also demonstrate how considering the genomic context of a gene tree can assist in more accurate determination of the true species phylogeny, especially in cases where a whole-genome phylogeny appears to be an unresolvable polytomy.
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Affiliation(s)
- James B Pease
- Department of Biology, Indiana University, Bloomington, Indiana 47405, USA.
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23
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Chong RA, Mueller RL. Low metabolic rates in salamanders are correlated with weak selective constraints on mitochondrial genes. Evolution 2012; 67:894-9. [PMID: 23461338 DOI: 10.1111/j.1558-5646.2012.01830.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Mitochondria are the site for the citric acid cycle and oxidative phosphorylation (OXPHOS), the final steps of ATP synthesis via cellular respiration. Each mitochondrion contains its own genome; in vertebrates, this is a small, circular DNA molecule that encodes 13 subunits of the multiprotein OXPHOS electron transport complexes. Vertebrate lineages vary dramatically in metabolic rates; thus, functional constraints on mitochondrial-encoded proteins likely differ, potentially impacting mitochondrial genome evolution. Here, we examine mitochondrial genome evolution in salamanders, which have the lowest metabolic requirements among tetrapods. We show that salamanders experience weaker purifying selection on protein-coding sequences than do frogs, a comparable amphibian clade with higher metabolic rates. In contrast, we find no evidence for weaker selection against mitochondrial genome expansion in salamanders. Together, these results suggest that different aspects of mitochondrial genome evolution (i.e., nucleotide substitution, accumulation of noncoding sequences) are differently affected by metabolic variation across tetrapod lineages.
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Affiliation(s)
- Rebecca A Chong
- Department of Biology, Colorado State University, Fort Collins, Colorado 80523-1878, USA.
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