1
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Louder MIM, Justen H, Kimmitt AA, Lawley KS, Turner LM, Dickman JD, Delmore KE. Gene regulation and speciation in a migratory divide between songbirds. Nat Commun 2024; 15:98. [PMID: 38167733 PMCID: PMC10761872 DOI: 10.1038/s41467-023-44352-2] [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: 04/16/2023] [Accepted: 12/11/2023] [Indexed: 01/05/2024] Open
Abstract
Behavioral variation abounds in nature. This variation is important for adaptation and speciation, but its molecular basis remains elusive. Here, we use a hybrid zone between two subspecies of songbirds that differ in migration - an ecologically important and taxonomically widespread behavior---to gain insight into this topic. We measure gene expression in five brain regions. Differential expression between migratory states was dominated by circadian genes in all brain regions. The remaining patterns were largely brain-region specific. For example, expression differences between the subspecies that interact with migratory state likely help maintain reproductive isolation in this system and were documented in only three brain regions. Contrary to existing work on regulatory mechanisms underlying species-specific traits, two lines of evidence suggest that trans- (vs. cis) regulatory changes underlie these patterns - no evidence for allele-specific expression in hybrids and minimal associations between genomic differentiation and expression differences. Additional work with hybrids shows expression levels were often distinct (transgressive) from parental forms. Behavioral contrasts and functional enrichment analyses allowed us to connect these patterns to mitonuclear incompatibilities and compensatory responses to stress that could exacerbate selection on hybrids and contribute to speciation.
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Affiliation(s)
| | - Hannah Justen
- Biology Department, Texas A&M University, College Station, TX, USA
| | | | - Koedi S Lawley
- Department of Veterinary Integrative Biosciences, School of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, TX, USA
| | - Leslie M Turner
- Milner Centre for Evolution, Department of Biology & Biochemistry, University of Bath, Bath, UK
| | - J David Dickman
- Department of Neuroscience, Baylor College of Medicine, Houston, TX, USA
| | - Kira E Delmore
- Biology Department, Texas A&M University, College Station, TX, USA.
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2
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Cutter AD. Speciation and development. Evol Dev 2023; 25:289-327. [PMID: 37545126 DOI: 10.1111/ede.12454] [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: 03/07/2023] [Revised: 06/13/2023] [Accepted: 07/20/2023] [Indexed: 08/08/2023]
Abstract
Understanding general principles about the origin of species remains one of the foundational challenges in evolutionary biology. The genomic divergence between groups of individuals can spawn hybrid inviability and hybrid sterility, which presents a tantalizing developmental problem. Divergent developmental programs may yield either conserved or divergent phenotypes relative to ancestral traits, both of which can be responsible for reproductive isolation during the speciation process. The genetic mechanisms of developmental evolution involve cis- and trans-acting gene regulatory change, protein-protein interactions, genetic network structures, dosage, and epigenetic regulation, all of which also have roots in population genetic and molecular evolutionary processes. Toward the goal of demystifying Darwin's "mystery of mysteries," this review integrates microevolutionary concepts of genetic change with principles of organismal development, establishing explicit links between population genetic process and developmental mechanisms in the production of macroevolutionary pattern. This integration aims to establish a more unified view of speciation that binds process and mechanism.
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Affiliation(s)
- Asher D Cutter
- Department of Ecology & Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada
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3
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Baier F, Gauye F, Perez-Carrasco R, Payne JL, Schaerli Y. Environment-dependent epistasis increases phenotypic diversity in gene regulatory networks. SCIENCE ADVANCES 2023; 9:eadf1773. [PMID: 37224262 DOI: 10.1126/sciadv.adf1773] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2022] [Accepted: 04/17/2023] [Indexed: 05/26/2023]
Abstract
Mutations to gene regulatory networks can be maladaptive or a source of evolutionary novelty. Epistasis confounds our understanding of how mutations affect the expression patterns of gene regulatory networks, a challenge exacerbated by the dependence of epistasis on the environment. We used the toolkit of synthetic biology to systematically assay the effects of pairwise and triplet combinations of mutant genotypes on the expression pattern of a gene regulatory network expressed in Escherichia coli that interprets an inducer gradient across a spatial domain. We uncovered a preponderance of epistasis that can switch in magnitude and sign across the inducer gradient to produce a greater diversity of expression pattern phenotypes than would be possible in the absence of such environment-dependent epistasis. We discuss our findings in the context of the evolution of hybrid incompatibilities and evolutionary novelties.
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Affiliation(s)
- Florian Baier
- Department of Fundamental Microbiology, University of Lausanne, Biophore Building, 1015 Lausanne, Switzerland
| | - Florence Gauye
- Department of Fundamental Microbiology, University of Lausanne, Biophore Building, 1015 Lausanne, Switzerland
| | | | - Joshua L Payne
- Institute of Integrative Biology, ETH Zurich, 8092 Zurich, Switzerland
| | - Yolanda Schaerli
- Department of Fundamental Microbiology, University of Lausanne, Biophore Building, 1015 Lausanne, Switzerland
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4
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Mahmud M, Bekele M, Behera N. A computational investigation of cis-gene regulation in evolution. Theory Biosci 2023; 142:151-165. [PMID: 37041403 DOI: 10.1007/s12064-023-00391-3] [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: 01/13/2022] [Accepted: 03/27/2023] [Indexed: 04/13/2023]
Abstract
In biological processes involving gene networks, genes regulate other genes that determine the phenotypic traits. Gene regulation plays an important role in evolutionary dynamics. In a genetic algorithm, a trans-gene regulatory mechanism was shown to speed up adaptation and evolution. Here, we examine the effect of cis-gene regulation on an adaptive system. The model is haploid. A chromosome is partitioned into regulatory loci and structural loci. The regulatory genes regulate the expression and functioning of structural genes via the cis-elements in a probabilistic manner. In the simulation, the change in the allele frequency, the mean population fitness and the efficiency of phenotypic selection are monitored. Cis-gene regulation increases adaption and accelerates the evolutionary process in comparison with the case involving absence of gene regulation. Some special features of the simulation results are as follows. A low ratio of regulatory loci and structural loci gives higher adaptation for fixed total number of loci. Plasticity is advantageous beyond a threshold value. Adaptation is better for large number of total loci when the ratio of regulatory loci to structural loci is one. However, it reaches a saturation beyond which the increase in the total loci is not advantageous. Efficiency of the phenotypic selection is higher for larger value of the initial plasticity.
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Affiliation(s)
- Mohammed Mahmud
- Department of Physics, Addis Ababa University, P.O.Box 1176, Addis Ababa, Ethiopia
| | - Mulugeta Bekele
- Department of Physics, Addis Ababa University, P.O.Box 1176, Addis Ababa, Ethiopia
| | - Narayan Behera
- Department of Applied Physics, Adama Science and Technology University, P. O. Box 1888, Adama, Ethiopia.
- Division of Physical Science, SVYASA University, Eknath Bhavan, Kempegowda Nagar, Bengaluru, 560019, India.
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5
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Abstract
Even if a species' phenotype does not change over evolutionary time, the underlying mechanism may change, as distinct molecular pathways can realize identical phenotypes. Here we use linear system theory to explore the consequences of this idea, describing how a gene network underlying a conserved phenotype evolves, as the genetic drift of small changes to these molecular pathways causes a population to explore the set of mechanisms with identical phenotypes. To do this, we model an organism's internal state as a linear system of differential equations for which the environment provides input and the phenotype is the output, in which context there exists an exact characterization of the set of all mechanisms that give the same input-output relationship. This characterization implies that selectively neutral directions in genotype space should be common and that the evolutionary exploration of these distinct but equivalent mechanisms can lead to the reproductive incompatibility of independently evolving populations. This evolutionary exploration, or system drift, is expected to proceed at a rate proportional to the amount of intrapopulation genetic variation divided by the effective population size ( Ne$N_e$ ). At biologically reasonable parameter values this could lead to substantial interpopulation incompatibility, and thus speciation, on a time scale of Ne$N_e$ generations. This model also naturally predicts Haldane's rule, thus providing a concrete explanation of why heterogametic hybrids tend to be disrupted more often than homogametes during the early stages of speciation.
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Affiliation(s)
- Joshua S. Schiffman
- New York Genome CenterNew YorkNew York 10013,Weill Cornell MedicineNew YorkNew York 10065,Department of Molecular and Computational BiologyUniversity of Southern CaliforniaLos AngelesCalifornia 90089
| | - Peter L. Ralph
- Department of Molecular and Computational BiologyUniversity of Southern CaliforniaLos AngelesCalifornia 90089,Department of Mathematics, Institute of Ecology and EvolutionUniversity of OregonEugeneOregon 97403,Department of Biology, Institute of Ecology and EvolutionUniversity of OregonEugeneOregon 97403
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6
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Stöck M, Dedukh D, Reifová R, Lamatsch DK, Starostová Z, Janko K. Sex chromosomes in meiotic, hemiclonal, clonal and polyploid hybrid vertebrates: along the 'extended speciation continuum'. Philos Trans R Soc Lond B Biol Sci 2021; 376:20200103. [PMID: 34304588 PMCID: PMC8310718 DOI: 10.1098/rstb.2020.0103] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/12/2021] [Indexed: 12/15/2022] Open
Abstract
We review knowledge about the roles of sex chromosomes in vertebrate hybridization and speciation, exploring a gradient of divergences with increasing reproductive isolation (speciation continuum). Under early divergence, well-differentiated sex chromosomes in meiotic hybrids may cause Haldane-effects and introgress less easily than autosomes. Undifferentiated sex chromosomes are more susceptible to introgression and form multiple (or new) sex chromosome systems with hardly predictable dominance hierarchies. Under increased divergence, most vertebrates reach complete intrinsic reproductive isolation. Slightly earlier, some hybrids (linked in 'the extended speciation continuum') exhibit aberrant gametogenesis, leading towards female clonality. This facilitates the evolution of various allodiploid and allopolyploid clonal ('asexual') hybrid vertebrates, where 'asexuality' might be a form of intrinsic reproductive isolation. A comprehensive list of 'asexual' hybrid vertebrates shows that they all evolved from parents with divergences that were greater than at the intraspecific level (K2P-distances of greater than 5-22% based on mtDNA). These 'asexual' taxa inherited genetic sex determination by mostly undifferentiated sex chromosomes. Among the few known sex-determining systems in hybrid 'asexuals', female heterogamety (ZW) occurred about twice as often as male heterogamety (XY). We hypothesize that pre-/meiotic aberrations in all-female ZW-hybrids present Haldane-effects promoting their evolution. Understanding the preconditions to produce various clonal or meiotic allopolyploids appears crucial for insights into the evolution of sex, 'asexuality' and polyploidy. This article is part of the theme issue 'Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part II)'.
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Affiliation(s)
- Matthias Stöck
- Leibniz-Institute of Freshwater Ecology and Inland Fisheries - IGB (Forschungsverbund Berlin), Müggelseedamm 301, 12587 Berlin, Germany
- Amphibian Research Center, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
| | - Dmitrij Dedukh
- Institute of Animal Physiology and Genetics, Laboratory of Fish Genetics, The Czech Academy of Sciences, 277 21 Libechov, Czech Republic
| | - Radka Reifová
- Department of Zoology, Faculty of Science, Charles University, Viničná 7, Prague 2, 128 00, Czech Republic
| | - Dunja K. Lamatsch
- Research Department for Limnology, University of Innsbruck, Mondseestrasse 9, A-5310 Mondsee, Austria
| | - Zuzana Starostová
- Department of Zoology, Faculty of Science, Charles University, Viničná 7, Prague 2, 128 00, Czech Republic
| | - Karel Janko
- Institute of Animal Physiology and Genetics, Laboratory of Fish Genetics, The Czech Academy of Sciences, 277 21 Libechov, Czech Republic
- Department of Biology and Ecology, Faculty of Science, University of Ostrava, 701 03 Ostrava, Czech Republic
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7
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Moran BM, Payne C, Langdon Q, Powell DL, Brandvain Y, Schumer M. The genomic consequences of hybridization. eLife 2021; 10:e69016. [PMID: 34346866 PMCID: PMC8337078 DOI: 10.7554/elife.69016] [Citation(s) in RCA: 78] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Accepted: 07/09/2021] [Indexed: 12/29/2022] Open
Abstract
In the past decade, advances in genome sequencing have allowed researchers to uncover the history of hybridization in diverse groups of species, including our own. Although the field has made impressive progress in documenting the extent of natural hybridization, both historical and recent, there are still many unanswered questions about its genetic and evolutionary consequences. Recent work has suggested that the outcomes of hybridization in the genome may be in part predictable, but many open questions about the nature of selection on hybrids and the biological variables that shape such selection have hampered progress in this area. We synthesize what is known about the mechanisms that drive changes in ancestry in the genome after hybridization, highlight major unresolved questions, and discuss their implications for the predictability of genome evolution after hybridization.
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Affiliation(s)
- Benjamin M Moran
- Department of Biology, Stanford UniversityStanfordUnited States
- Centro de Investigaciones Científicas de las Huastecas “Aguazarca”HidalgoMexico
| | - Cheyenne Payne
- Department of Biology, Stanford UniversityStanfordUnited States
- Centro de Investigaciones Científicas de las Huastecas “Aguazarca”HidalgoMexico
| | - Quinn Langdon
- Department of Biology, Stanford UniversityStanfordUnited States
| | - Daniel L Powell
- Department of Biology, Stanford UniversityStanfordUnited States
- Centro de Investigaciones Científicas de las Huastecas “Aguazarca”HidalgoMexico
| | - Yaniv Brandvain
- Department of Ecology, Evolution & Behavior and Plant and Microbial Biology, University of MinnesotaMinneapolisUnited States
| | - Molly Schumer
- Department of Biology, Stanford UniversityStanfordUnited States
- Centro de Investigaciones Científicas de las Huastecas “Aguazarca”HidalgoMexico
- Hanna H. Gray Fellow, Howard Hughes Medical InstituteStanfordUnited States
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8
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Manrubia S, Cuesta JA, Aguirre J, Ahnert SE, Altenberg L, Cano AV, Catalán P, Diaz-Uriarte R, Elena SF, García-Martín JA, Hogeweg P, Khatri BS, Krug J, Louis AA, Martin NS, Payne JL, Tarnowski MJ, Weiß M. From genotypes to organisms: State-of-the-art and perspectives of a cornerstone in evolutionary dynamics. Phys Life Rev 2021; 38:55-106. [PMID: 34088608 DOI: 10.1016/j.plrev.2021.03.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2020] [Accepted: 03/01/2021] [Indexed: 12/21/2022]
Abstract
Understanding how genotypes map onto phenotypes, fitness, and eventually organisms is arguably the next major missing piece in a fully predictive theory of evolution. We refer to this generally as the problem of the genotype-phenotype map. Though we are still far from achieving a complete picture of these relationships, our current understanding of simpler questions, such as the structure induced in the space of genotypes by sequences mapped to molecular structures, has revealed important facts that deeply affect the dynamical description of evolutionary processes. Empirical evidence supporting the fundamental relevance of features such as phenotypic bias is mounting as well, while the synthesis of conceptual and experimental progress leads to questioning current assumptions on the nature of evolutionary dynamics-cancer progression models or synthetic biology approaches being notable examples. This work delves with a critical and constructive attitude into our current knowledge of how genotypes map onto molecular phenotypes and organismal functions, and discusses theoretical and empirical avenues to broaden and improve this comprehension. As a final goal, this community should aim at deriving an updated picture of evolutionary processes soundly relying on the structural properties of genotype spaces, as revealed by modern techniques of molecular and functional analysis.
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Affiliation(s)
- Susanna Manrubia
- Department of Systems Biology, Centro Nacional de Biotecnología (CSIC), Madrid, Spain; Grupo Interdisciplinar de Sistemas Complejos (GISC), Madrid, Spain.
| | - José A Cuesta
- Grupo Interdisciplinar de Sistemas Complejos (GISC), Madrid, Spain; Departamento de Matemáticas, Universidad Carlos III de Madrid, Leganés, Spain; Instituto de Biocomputación y Física de Sistemas Complejos (BiFi), Universidad de Zaragoza, Spain; UC3M-Santander Big Data Institute (IBiDat), Getafe, Madrid, Spain
| | - Jacobo Aguirre
- Grupo Interdisciplinar de Sistemas Complejos (GISC), Madrid, Spain; Centro de Astrobiología, CSIC-INTA, ctra. de Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain
| | - Sebastian E Ahnert
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge CB3 0AS, UK; The Alan Turing Institute, British Library, 96 Euston Road, London NW1 2DB, UK
| | | | - Alejandro V Cano
- Institute of Integrative Biology, ETH Zurich, Zurich, Switzerland; Swiss Institute of Bioinformatics, Lausanne, Switzerland
| | - Pablo Catalán
- Grupo Interdisciplinar de Sistemas Complejos (GISC), Madrid, Spain; Departamento de Matemáticas, Universidad Carlos III de Madrid, Leganés, Spain
| | - Ramon Diaz-Uriarte
- Department of Biochemistry, Universidad Autónoma de Madrid, Madrid, Spain; Instituto de Investigaciones Biomédicas "Alberto Sols" (UAM-CSIC), Madrid, Spain
| | - Santiago F Elena
- Instituto de Biología Integrativa de Sistemas, I(2)SysBio (CSIC-UV), València, Spain; The Santa Fe Institute, Santa Fe, NM, USA
| | | | - Paulien Hogeweg
- Theoretical Biology and Bioinformatics Group, Utrecht University, the Netherlands
| | - Bhavin S Khatri
- The Francis Crick Institute, London, UK; Department of Life Sciences, Imperial College London, London, UK
| | - Joachim Krug
- Institute for Biological Physics, University of Cologne, Köln, Germany
| | - Ard A Louis
- Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford, UK
| | - Nora S Martin
- Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, Cambridge, UK; Sainsbury Laboratory, University of Cambridge, Cambridge, UK
| | - Joshua L Payne
- Institute of Integrative Biology, ETH Zurich, Zurich, Switzerland; Swiss Institute of Bioinformatics, Lausanne, Switzerland
| | | | - Marcel Weiß
- Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, Cambridge, UK; Sainsbury Laboratory, University of Cambridge, Cambridge, UK
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9
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Mugal CF, Wang M, Backström N, Wheatcroft D, Ålund M, Sémon M, McFarlane SE, Dutoit L, Qvarnström A, Ellegren H. Tissue-specific patterns of regulatory changes underlying gene expression differences among Ficedula flycatchers and their naturally occurring F 1 hybrids. Genome Res 2020; 30:1727-1739. [PMID: 33144405 PMCID: PMC7706733 DOI: 10.1101/gr.254508.119] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Accepted: 10/28/2020] [Indexed: 12/27/2022]
Abstract
Changes in interacting cis- and trans-regulatory elements are important candidates for Dobzhansky-Muller hybrid incompatibilities and may contribute to hybrid dysfunction by giving rise to misexpression in hybrids. To gain insight into the molecular mechanisms and determinants of gene expression evolution in natural populations, we analyzed the transcriptome from multiple tissues of two recently diverged Ficedula flycatcher species and their naturally occurring F1 hybrids. Differential gene expression analysis revealed that the extent of differentiation between species and the set of differentially expressed genes varied across tissues. Common to all tissues, a higher proportion of Z-linked genes than autosomal genes showed differential expression, providing evidence for a fast-Z effect. We further found clear signatures of hybrid misexpression in brain, heart, kidney, and liver. However, while testis showed the highest divergence of gene expression among tissues, it showed no clear signature of misexpression in F1 hybrids, even though these hybrids were found to be sterile. It is therefore unlikely that incompatibilities between cis-trans regulatory changes explain the observed sterility. Instead, we found evidence that cis-regulatory changes play a significant role in the evolution of gene expression in testis, which illustrates the tissue-specific nature of cis-regulatory evolution bypassing constraints associated with pleiotropic effects of genes.
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Affiliation(s)
- Carina F Mugal
- Department of Ecology and Genetics, Uppsala University, 752 36 Uppsala, Sweden
| | - Mi Wang
- Department of Ecology and Genetics, Uppsala University, 752 36 Uppsala, Sweden
| | - Niclas Backström
- Department of Ecology and Genetics, Uppsala University, 752 36 Uppsala, Sweden
| | - David Wheatcroft
- Department of Ecology and Genetics, Uppsala University, 752 36 Uppsala, Sweden.,Department of Zoology, Stockholm University, 106 91 Stockholm, Sweden
| | - Murielle Ålund
- Department of Ecology and Genetics, Uppsala University, 752 36 Uppsala, Sweden.,Department of Integrative Biology, Michigan State University, East Lansing, Michigan 48824, USA
| | - Marie Sémon
- Department of Ecology and Genetics, Uppsala University, 752 36 Uppsala, Sweden.,ENS de Lyon, Laboratory of Biology and Modelling of the Cell, Lyon University, 69364 Lyon Cedex 07, France
| | - S Eryn McFarlane
- Department of Ecology and Genetics, Uppsala University, 752 36 Uppsala, Sweden.,Institute of Evolutionary Biology, University of Edinburgh, Edinburgh EH9 3FL, United Kingdom
| | - Ludovic Dutoit
- Department of Ecology and Genetics, Uppsala University, 752 36 Uppsala, Sweden.,Department of Zoology, University of Otago, Dunedin 9016, New Zealand
| | - Anna Qvarnström
- Department of Ecology and Genetics, Uppsala University, 752 36 Uppsala, Sweden
| | - Hans Ellegren
- Department of Ecology and Genetics, Uppsala University, 752 36 Uppsala, Sweden
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10
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Abstract
New species arise as the genomes of populations diverge. The developmental 'alarm clock' of speciation sounds off when sufficient divergence in genetic control of development leads hybrid individuals to infertility or inviability, the world awoken to the dawn of new species with intrinsic post-zygotic reproductive isolation. Some developmental stages will be more prone to hybrid dysfunction due to how molecular evolution interacts with the ontogenetic timing of gene expression. Considering the ontogeny of hybrid incompatibilities provides a profitable connection between 'evo-devo' and speciation genetics to better link macroevolutionary pattern, microevolutionary process, and molecular mechanisms. Here, we explore speciation alongside development, emphasizing their mutual dependence on genetic network features, fitness landscapes, and developmental system drift. We assess models for how ontogenetic timing of reproductive isolation can be predictable. Experiments and theory within this synthetic perspective can help identify new rules of speciation as well as rules in the molecular evolution of development.
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Affiliation(s)
- Asher D Cutter
- Department of Ecology & Evolutionary Biology, University of TorontoTorontoCanada
| | - Joanna D Bundus
- Department of Integrative Biology, University of Wisconsin – MadisonMadisonUnited States
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11
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McGirr JA, Martin CH. Ecological divergence in sympatry causes gene misexpression in hybrids. Mol Ecol 2020; 29:2707-2721. [PMID: 32557903 DOI: 10.1111/mec.15512] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Revised: 05/21/2020] [Accepted: 06/01/2020] [Indexed: 12/17/2022]
Abstract
Ecological speciation occurs when reproductive isolation evolves as a byproduct of adaptive divergence between populations. Selection favouring gene regulatory divergence between species could result in transgressive levels of gene expression in F1 hybrids that may lower hybrid fitness. We combined 58 resequenced genomes with 124 transcriptomes to identify patterns of hybrid gene misexpression that may be driven by adaptive regulatory divergence within a young radiation of Cyprinodon pupfishes, which consists of a dietary generalist and two trophic specialists-a molluscivore and a scale-eater. We found more differential gene expression between closely related sympatric specialists than between allopatric generalist populations separated by 1,000 km. Intriguingly, 9.6% of genes that were differentially expressed between sympatric species were also misexpressed in F1 hybrids. A subset of these genes were in highly differentiated genomic regions and enriched for functions important for trophic specialization, including head, muscle and brain development. These regions also included genes that showed evidence of hard selective sweeps and were significantly associated with oral jaw length-the most rapidly diversifying skeletal trait in this radiation. Our results indicate that divergent ecological selection in sympatry can contribute to hybrid gene misexpression which may act as a reproductive barrier between nascent species.
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Affiliation(s)
- Joseph A McGirr
- Department of Biology, University of North Carolina, Chapel Hill, NC
| | - Christopher H Martin
- Department of Biology, University of North Carolina, Chapel Hill, NC.,Department of Integrative Biology and Museum of Vertebrate Zoology, University of California, Berkeley, CA
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12
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Parthenogenesis as a Solution to Hybrid Sterility: The Mechanistic Basis of Meiotic Distortions in Clonal and Sterile Hybrids. Genetics 2020; 215:975-987. [PMID: 32518062 PMCID: PMC7404241 DOI: 10.1534/genetics.119.302988] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2019] [Accepted: 06/03/2020] [Indexed: 11/25/2022] Open
Abstract
Hybrid sterility is a hallmark of speciation, but the underlying molecular mechanisms remain poorly understood. Here, we report that speciation may regularly proceed through a stage at which gene flow is completely interrupted, but hybrid sterility occurs only in male hybrids whereas female hybrids reproduce asexually. We analyzed gametogenic pathways in hybrids between the fish species Cobitis elongatoides and C. taenia, and revealed that male hybrids were sterile owing to extensive asynapsis and crossover reduction among heterospecific chromosomal pairs in their gametes, which was subsequently followed by apoptosis. We found that polyploidization allowed pairing between homologous chromosomes and therefore partially rescued the bivalent formation and crossover rates in triploid hybrid males. However, it was not sufficient to overcome sterility. In contrast, both diploid and triploid hybrid females exhibited premeiotic genome endoreplication, thereby ensuring proper bivalent formation between identical chromosomal copies. This endoreplication ultimately restored female fertility but it simultaneously resulted in the obligate production of clonal gametes, preventing any interspecific gene flow. In conclusion, we demonstrate that the emergence of asexuality can remedy hybrid sterility in a sex-specific manner and contributes to the speciation process.
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13
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Bartoš O, Röslein J, Kotusz J, Paces J, Pekárik L, Petrtýl M, Halačka K, Štefková Kašparová E, Mendel J, Boroń A, Juchno D, Leska A, Jablonska O, Benes V, Šídová M, Janko K. The Legacy of Sexual Ancestors in Phenotypic Variability, Gene Expression, and Homoeolog Regulation of Asexual Hybrids and Polyploids. Mol Biol Evol 2020; 36:1902-1920. [PMID: 31077330 PMCID: PMC6735777 DOI: 10.1093/molbev/msz114] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Hybridization and polyploidization are important evolutionary processes whose impacts range from the alteration of gene expression and phenotypic variation to the triggering of asexual reproduction. We investigated fishes of the Cobitis taenia-elongatoides hybrid complex, which allowed us to disentangle the direct effects of both processes, due to the co-occurrence of parental species with their diploid and triploid hybrids. Employing morphological, ecological, and RNAseq approaches, we investigated the molecular determinants of hybrid and polyploid forms. In contrast with other studies, hybridization and polyploidy induced relatively very little transgressivity. Instead, Cobitis hybrids appeared intermediate with a clear effect of genomic dosing when triploids expressed higher similarity to the parent contributing two genome sets. This dosage effect was symmetric in the germline (oocyte gene expression), interestingly though, we observed an overall bias toward C. taenia in somatic tissues and traits. At the level of individual genes, expression-level dominance vastly prevailed over additivity or transgressivity. Also, trans-regulation of gene expression was less efficient in diploid hybrids than in triploids, where the expression modulation of homoeologs derived from the "haploid" parent was stronger than those derived from the "diploid" parent. Our findings suggest that the apparent intermediacy of hybrid phenotypes results from the combination of individual genes with dominant expression rather than from simple additivity. The efficiency of cross-talk between trans-regulatory elements further appears dosage dependent. Important effects of polyploidization may thus stem from changes in relative concentrations of trans-regulatory elements and their binding sites between hybridizing genomes. Links between gene regulation and asexuality are discussed.
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Affiliation(s)
- Oldřich Bartoš
- Institute of Animal Physiology and Genetics, Laboratory of Fish Genetics, The Czech Academy of Sciences, Libechov, Czech Republic.,Department of Zoology, Faculty of Science, Charles University, Prague, Czech Republic
| | - Jan Röslein
- Institute of Animal Physiology and Genetics, Laboratory of Fish Genetics, The Czech Academy of Sciences, Libechov, Czech Republic.,Department of Biology and Ecology, Faculty of Science, University of Ostrava, Ostrava, Czech Republic
| | - Jan Kotusz
- Museum of Natural History, University of Wroclaw, Wroclaw, Poland
| | - Jan Paces
- Institute of Animal Physiology and Genetics, Laboratory of Fish Genetics, The Czech Academy of Sciences, Libechov, Czech Republic.,Institute of Molecular Genetics, Laboratory of Genomics and Bioinformatics, The Czech Academy of Sciences, Prague, Czech Republic
| | - Ladislav Pekárik
- Plant Science and Biodiversity Center, Institute of Botany, Slovak Academy of Sciences, Bratislava, Slovakia.,Faculty of Education, Trnava University, Trnava, Slovakia
| | - Miloslav Petrtýl
- Institute of Animal Physiology and Genetics, Laboratory of Fish Genetics, The Czech Academy of Sciences, Libechov, Czech Republic.,Department of Zoology and Fisheries, Faculty of Agrobiology, Food and Natural Resources, Czech University of Life Sciences Prague, Prague, Czech Republic
| | - Karel Halačka
- Institute of Vertebrate Biology, Czech Academy of Sciences, Brno, Czech Republic
| | - Eva Štefková Kašparová
- Institute of Animal Physiology and Genetics, Laboratory of Fish Genetics, The Czech Academy of Sciences, Libechov, Czech Republic
| | - Jan Mendel
- Institute of Vertebrate Biology, Czech Academy of Sciences, Brno, Czech Republic
| | - Alicja Boroń
- Department of Zoology, Faculty of Biology and Biotechnology, University of Warmia and Mazury in Olsztyn, Olsztyn, Poland
| | - Dorota Juchno
- Department of Zoology, Faculty of Biology and Biotechnology, University of Warmia and Mazury in Olsztyn, Olsztyn, Poland
| | - Anna Leska
- Department of Zoology, Faculty of Biology and Biotechnology, University of Warmia and Mazury in Olsztyn, Olsztyn, Poland
| | - Olga Jablonska
- Department of Zoology, Faculty of Biology and Biotechnology, University of Warmia and Mazury in Olsztyn, Olsztyn, Poland
| | - Vladimir Benes
- Genomics Core Facility, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
| | - Monika Šídová
- Institute of Biotechnology of the Czech Academy of Sciences - BIOCEV, Vestec, Czech Republic
| | - Karel Janko
- Institute of Animal Physiology and Genetics, Laboratory of Fish Genetics, The Czech Academy of Sciences, Libechov, Czech Republic.,Department of Biology and Ecology, Faculty of Science, University of Ostrava, Ostrava, Czech Republic
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14
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Negri A, Jąkalski M, Szczuka A, Pryszcz LP, Mruk I. Transcriptome analyses of cells carrying the Type II Csp231I restriction-modification system reveal cross-talk between two unrelated transcription factors: C protein and the Rac prophage repressor. Nucleic Acids Res 2019; 47:9542-9556. [PMID: 31372643 PMCID: PMC6765115 DOI: 10.1093/nar/gkz665] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2019] [Revised: 07/16/2019] [Accepted: 07/23/2019] [Indexed: 12/27/2022] Open
Abstract
Restriction-modification (R–M) systems represent an effective mechanism of defence against invading bacteriophages, and are widely spread among bacteria and archaea. In acquiring a Type II R–M system via horizontal gene transfer, the new hosts become more resistant to phage infection, through the action of a restriction endonuclease (REase), which recognizes and cleaves specific target DNAs. To protect the host cell's DNA, there is also a methyltransferase (MTase), which prevents DNA cleavage by the cognate REase. In some R–M systems, the host also accepts a cis-acting transcription factor (C protein), which regulates the counteracting activities of REase and MTase to avoid host self-restriction. Our study characterized the unexpected phenotype of Escherichia coli cells, which manifested as extensive cell filamentation triggered by acquiring the Csp231I R–M system from Citrobacter sp. Surprisingly, we found that the cell morphology defect was solely dependent on the C regulator. Our transcriptome analysis supported by in vivo and in vitro assays showed that C protein directly silenced the expression of the RacR repressor to affect the Rac prophage-related genes. The rac locus ydaST genes, when derepressed, exerted a toxicity indicated by cell filamentation through an unknown mechanism. These results provide an apparent example of transcription factor cross-talk, which can have significant consequences for the host, and may represent a constraint on lateral gene transfer.
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Affiliation(s)
- Alessandro Negri
- Department of Microbiology, Faculty of Biology, University of Gdansk, Wita Stwosza 59, Gdansk 80-308, Poland
| | - Marcin Jąkalski
- Department of Plant Taxonomy and Nature Conservation, University of Gdansk, Wita Stwosza 59, 80-308 Gdansk, Poland
| | - Aleksandra Szczuka
- Department of Microbiology, Faculty of Biology, University of Gdansk, Wita Stwosza 59, Gdansk 80-308, Poland
| | - Leszek P Pryszcz
- Laboratory of Zebrafish Developmental Genomics, International Institute of Molecular and Cell Biology, Warsaw, ul. Trojdena 4, 02-109 Warsaw, Poland
| | - Iwona Mruk
- Department of Microbiology, Faculty of Biology, University of Gdansk, Wita Stwosza 59, Gdansk 80-308, Poland
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15
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Khatri BS, Goldstein RA. Biophysics and population size constrains speciation in an evolutionary model of developmental system drift. PLoS Comput Biol 2019; 15:e1007177. [PMID: 31335870 PMCID: PMC6677325 DOI: 10.1371/journal.pcbi.1007177] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2018] [Revised: 08/02/2019] [Accepted: 06/13/2019] [Indexed: 02/06/2023] Open
Abstract
Developmental system drift is a likely mechanism for the origin of hybrid incompatibilities between closely related species. We examine here the detailed mechanistic basis of hybrid incompatibilities between two allopatric lineages, for a genotype-phenotype map of developmental system drift under stabilising selection, where an organismal phenotype is conserved, but the underlying molecular phenotypes and genotype can drift. This leads to number of emergent phenomenon not obtainable by modelling genotype or phenotype alone. Our results show that: 1) speciation is more rapid at smaller population sizes with a characteristic, Orr-like, power law, but at large population sizes slow, characterised by a sub-diffusive growth law; 2) the molecular phenotypes under weakest selection contribute to the earliest incompatibilities; and 3) pair-wise incompatibilities dominate over higher order, contrary to previous predictions that the latter should dominate. The population size effect we find is consistent with previous results on allopatric divergence of transcription factor-DNA binding, where smaller populations have common ancestors with a larger drift load because genetic drift favours phenotypes which have a larger number of genotypes (higher sequence entropy) over more fit phenotypes which have far fewer genotypes; this means less substitutions are required in either lineage before incompatibilities arise. Overall, our results indicate that biophysics and population size provide a much stronger constraint to speciation than suggested by previous models, and point to a general mechanistic principle of how incompatibilities arise the under stabilising selection for an organismal phenotype. The process of speciation is of fundamental importance to the field of evolution as it is intimately connected to understanding the immense bio-diversity of life. There is still relatively little understanding of the underlying genetic mechanisms that give rise to hybrid incompatibilities with results suggesting that divergence in transcription factor DNA binding and gene expression play an important role. A key finding from the field of evo-devo is that organismal phenotypes show developmental system drift, where species maintain the same phenotype, but diverge in developmental pathways; this is an important potential source of hybrid incompatibilities. Here, we explore a theoretical framework to understand how incompatibilities arise due to developmental system drift, using a tractable biophysically inspired genotype-phenotype for spatial gene expression. Modelling the evolution of phenotypes in this way has the key advantage that it mirrors how selection works in nature, i.e. that selection acts on phenotypes, but variation (mutation) arise at the level of genotypes. This results, as we demonstrate, in a number of non-trivial and testable predictions concerning speciation due to developmental system drift, which would not be obtainable by modelling evolution of genotypes or phenotypes alone.
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Affiliation(s)
| | - Richard A. Goldstein
- Division of Infection & Immunity, University College London, London, United Kingdom
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16
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Whitlock AOB, Azevedo RBR, Burch CL. Population structure promotes the evolution of costly sex in artificial gene networks. Evolution 2019; 73:1089-1100. [PMID: 30997680 DOI: 10.1111/evo.13733] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2018] [Accepted: 03/25/2019] [Indexed: 11/30/2022]
Abstract
We build on previous observations that Hill-Robertson interference generates an advantage of sex that, in structured populations, can be large enough to explain the evolutionary maintenance of costly sex. We employed a gene network model that explicitly incorporates interactions between genes. Mutations in the gene networks have variable effects that depend on the genetic background in which they appear. Consequently, our simulations include two costs of sex-recombination and migration loads-that were missing from previous studies of the evolution of costly sex. Our results suggest a critical role for population structure that lies in its ability to align the long- and short-term advantages of sex. We show that the addition of population structure favored the evolution of sex by disproportionately decreasing the equilibrium mean fitness of asexual populations, primarily by increasing the strength of Muller's Ratchet. Population structure also increased the ability of the short-term advantage of sex to counter the primary limit to the evolution of sex in the gene network model-recombination load. On the other hand, highly structured populations experienced migration load in the form of Dobzhansky-Muller incompatibilities, decreasing the effective rate of migration between demes and, consequently, accelerating the accumulation of drift load in the sexual populations.
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Affiliation(s)
- Alexander O B Whitlock
- Curriculum in Genetics and Molecular Biology, University of North Carolina, Chapel Hill, North Carolina
| | - Ricardo B R Azevedo
- Department of Biology and Biochemistry, University of Houston, Houston, Texas
| | - Christina L Burch
- Biology Department, University of North Carolina, Chapel Hill, North Carolina
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17
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Collins-Hed AI, Ardell DH. Match fitness landscapes for macromolecular interaction networks: Selection for translational accuracy and rate can displace tRNA-binding interfaces of non-cognate aminoacyl-tRNA synthetases. Theor Popul Biol 2019; 129:68-80. [PMID: 31042487 DOI: 10.1016/j.tpb.2019.03.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Revised: 01/26/2019] [Accepted: 03/13/2019] [Indexed: 12/21/2022]
Abstract
Advances in structural biology of aminoacyl-tRNA synthetases (aaRSs) have revealed incredible diversity in how aaRSs bind their tRNA substrates. The causes of this diversity remain mysterious. We developed a new class of highly rugged fitness landscape models called match landscapes, through which genes encode the assortative interactions of their gene products through the complementarity and identifiability of their structural features. We used results from coding theory to prove bounds and equalities on fitness in match landscapes assuming additive interaction energies, macroscopic aminoacylation kinetics including proofreading, site-specific modifiers of interaction, and selection for translational accuracy in multiple, perfectly encoded site-types. Using genotypes based on extended Hamming codes we show that over a wide array of interface sizes and numbers of encoded cognate pairs, selection for translational accuracy alone is insufficient to displace the tRNA-binding interfaces of aaRSs. Yet, under combined selection for translational accuracy and rate, site-specific modifiers are selected to adaptively displace the tRNA-binding interfaces of non-cognate aaRS-tRNA pairs. We describe a remarkable correspondence between the lengths of perfect RNA (quaternary) codes and the modal sizes of small non-coding RNA families.
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Affiliation(s)
- Andrea I Collins-Hed
- Quantitative and Systems Biology Program, University of California, Merced, CA, 95306, United States
| | - David H Ardell
- Quantitative and Systems Biology Program, University of California, Merced, CA, 95306, United States; Molecular and Cell Biology Department, School of Natural Sciences, University of California, Merced, CA, 95306, United States.
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18
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Sciuchetti L, Dufresnes C, Cavoto E, Brelsford A, Perrin N. Dobzhansky-Muller incompatibilities, dominance drive, and sex-chromosome introgression at secondary contact zones: A simulation study. Evolution 2018; 72:1350-1361. [PMID: 29806172 DOI: 10.1111/evo.13510] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2017] [Accepted: 05/08/2018] [Indexed: 11/28/2022]
Abstract
Dobzhansky-Muller (DM) incompatibilities involving sex chromosomes have been proposed to account for Haldane's rule (lowered fitness among hybrid offspring of the heterogametic sex) as well as Darwin's corollary (asymmetric fitness costs with respect to the direction of the cross). We performed simulation studies of a hybrid zone to investigate the effects of different types of DM incompatibilities on cline widths and positions of sex-linked markers. From our simulations, X-Y incompatibilities generate steep clines for both X-linked and Y-linked markers; random effects may produce strong noise in cline center positions when migration is high relative to fitness costs, but X- and Y-centers always coincide strictly. X-autosome and Y-autosome incompatibilities also generate steep clines, but systematic shifts in cline centers occur when migration is high relative to selection, as a result of a dominance drive linked to Darwin's corollary. Interestingly, sex-linked genes always show farther introgression than the associated autosomal genes. We discuss ways of disentangling the potentially confounding effects of sex biases in migration, we compare our results to those of a few documented contact zones, and we stress the need to study independent replicates of the same contact zone.
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Affiliation(s)
- Luca Sciuchetti
- Department of Ecology & Evolution, University of Lausanne, Biophore Building, Lausanne, 1015, Switzerland
| | - Christophe Dufresnes
- Department of Ecology & Evolution, University of Lausanne, Biophore Building, Lausanne, 1015, Switzerland
- Department of Animal & Plant Sciences, University of Sheffield, Alfred Denny building, Western Bank, Sheffield, S10 2TN, United Kingdom
| | - Elisa Cavoto
- Department of Ecology & Evolution, University of Lausanne, Biophore Building, Lausanne, 1015, Switzerland
| | - Alan Brelsford
- Department of Ecology & Evolution, University of Lausanne, Biophore Building, Lausanne, 1015, Switzerland
- Biology Department, University of California, Riverside, CA, 92521
| | - Nicolas Perrin
- Department of Ecology & Evolution, University of Lausanne, Biophore Building, Lausanne, 1015, Switzerland
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19
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Spiraling Complexity: A Test of the Snowball Effect in a Computational Model of RNA Folding. Genetics 2016; 206:377-388. [PMID: 28007889 DOI: 10.1534/genetics.116.196030] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2016] [Accepted: 03/03/2017] [Indexed: 01/07/2023] Open
Abstract
Genetic incompatibilities can emerge as a byproduct of genetic divergence. According to Dobzhansky and Muller, an allele that fixes in one population may be incompatible with an allele at a different locus in another population when the two alleles are brought together in hybrids. Orr showed that the number of Dobzhansky-Muller incompatibilities (DMIs) should accumulate faster than linearly-i.e., snowball-as two lineages diverge. Several studies have attempted to test the snowball effect using data from natural populations. One limitation of these studies is that they have focused on predictions of the Orr model, but not on its underlying assumptions. Here, we use a computational model of RNA folding to test both predictions and assumptions of the Orr model. Two populations are allowed to evolve in allopatry on a holey fitness landscape. We find that the number of inviable introgressions (an indicator for the number of DMIs) snowballs, but does so more slowly than expected. We show that this pattern is explained, in part, by the fact that DMIs can disappear after they have arisen, contrary to the assumptions of the Orr model. This occurs because DMIs become progressively more complex (i.e., involve alleles at more loci) as a result of later substitutions. We also find that most DMIs involve >2 loci, i.e., they are complex. Reproductive isolation does not snowball because DMIs do not act independently of each other. We conclude that the RNA model supports the central prediction of the Orr model that the number of DMIs snowballs, but challenges other predictions, as well as some of its underlying assumptions.
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20
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Mack KL, Nachman MW. Gene Regulation and Speciation. Trends Genet 2016; 33:68-80. [PMID: 27914620 DOI: 10.1016/j.tig.2016.11.003] [Citation(s) in RCA: 109] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2016] [Revised: 11/06/2016] [Accepted: 11/07/2016] [Indexed: 11/17/2022]
Abstract
Understanding the genetic architecture of speciation is a major goal in evolutionary biology. Hybrid dysfunction is thought to arise most commonly through negative interactions between alleles at two or more loci. Divergence between interacting regulatory elements that affect gene expression (i.e., regulatory divergence) may be a common route for these negative interactions to arise. We review here how regulatory divergence between species can result in hybrid dysfunction, including recent theoretical support for this model. We then discuss the empirical evidence for regulatory divergence between species and evaluate evidence for misregulation as a source of hybrid dysfunction. Finally, we review unresolved questions in gene regulation as it pertains to speciation and point to areas that could benefit from future research.
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Affiliation(s)
- Katya L Mack
- Department of Integrative Biology and Museum of Vertebrate Zoology, University of California, Berkeley, CA 94720, USA
| | - Michael W Nachman
- Department of Integrative Biology and Museum of Vertebrate Zoology, University of California, Berkeley, CA 94720, USA.
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21
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A New Mechanism for Mendelian Dominance in Regulatory Genetic Pathways: Competitive Binding by Transcription Factors. Genetics 2016; 205:101-112. [PMID: 27866169 DOI: 10.1534/genetics.116.195255] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Accepted: 11/04/2016] [Indexed: 12/11/2022] Open
Abstract
We report a new mechanism for allelic dominance in regulatory genetic interactions that we call binding dominance. We investigated a biophysical model of gene regulation, where the fractional occupancy of a transcription factor (TF) on the cis-regulated promoter site it binds to is determined by binding energy (-ΔG) and TF dosage. Transcription and gene expression proceed when the TF is bound to the promoter. In diploids, individuals may be heterozygous at the cis-site, at the TF's coding region, or at the TF's own promoter, which determines allele-specific dosage. We find that when the TF's coding region is heterozygous, TF alleles compete for occupancy at the cis-sites and the tighter-binding TF is dominant in proportion to the difference in binding strength. When the TF's own promoter is heterozygous, the TF produced at the higher dosage is also dominant. Cis-site heterozygotes have additive expression and therefore codominant phenotypes. Binding dominance propagates to affect the expression of downstream loci and it is sensitive in both magnitude and direction to genetic background, but its detectability often attenuates. While binding dominance is inevitable at the molecular level, it is difficult to detect in the phenotype under some biophysical conditions, more so when TF dosage is high and allele-specific binding affinities are similar. A body of empirical research on the biophysics of TF binding demonstrates the plausibility of this mechanism of dominance, but studies of gene expression under competitive binding in heterozygotes in a diversity of genetic backgrounds are needed.
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22
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Neighboring genes for DNA-binding proteins rescue male sterility in Drosophila hybrids. Proc Natl Acad Sci U S A 2016; 113:E4200-7. [PMID: 27357670 DOI: 10.1073/pnas.1608337113] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Crosses between closely related animal species often result in male hybrids that are sterile, and the molecular and functional basis of genetic factors for hybrid male sterility is of great interest. Here, we report a molecular and functional analysis of HMS1, a region of 9.2 kb in chromosome 3 of Drosophila mauritiana, which results in virtually complete hybrid male sterility when homozygous in the genetic background of sibling species Drosophila simulans. The HMS1 region contains two strong candidate genes for the genetic incompatibility, agt and Taf1 Both encode unrelated DNA-binding proteins, agt for an alkyl-cysteine-S-alkyltransferase and Taf1 for a subunit of transcription factor TFIID that serves as a multifunctional transcriptional regulator. The contribution of each gene to hybrid male sterility was assessed by means of germ-line transformation, with constructs containing complete agt and Taf1 genomic sequences as well as various chimeric constructs. Both agt and Taf1 contribute about equally to HMS1 hybrid male sterility. Transgenes containing either locus rescue sterility in about one-half of the males, and among fertile males the number of offspring is in the normal range. This finding suggests compensatory proliferation of the rescued, nondysfunctional germ cells. Results with chimeric transgenes imply that the hybrid incompatibilities result from interactions among nucleotide differences residing along both agt and Taf1 Our results challenge a number of preliminary generalizations about the molecular and functional basis of hybrid male sterility, and strongly reinforce the role of DNA-binding proteins as a class of genes contributing to the maintenance of postzygotic reproductive isolation.
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23
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Uebbing S, Künstner A, Mäkinen H, Backström N, Bolivar P, Burri R, Dutoit L, Mugal CF, Nater A, Aken B, Flicek P, Martin FJ, Searle SMJ, Ellegren H. Divergence in gene expression within and between two closely related flycatcher species. Mol Ecol 2016; 25:2015-28. [PMID: 26928872 PMCID: PMC4879514 DOI: 10.1111/mec.13596] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Revised: 02/15/2016] [Accepted: 02/17/2016] [Indexed: 12/12/2022]
Abstract
Relatively little is known about the character of gene expression evolution as species diverge. It is for instance unclear if gene expression generally evolves in a clock‐like manner (by stabilizing selection or neutral evolution) or if there are frequent episodes of directional selection. To gain insights into the evolutionary divergence of gene expression, we sequenced and compared the transcriptomes of multiple organs from population samples of collared (Ficedula albicollis) and pied flycatchers (F. hypoleuca), two species which diverged less than one million years ago. Ordination analysis separated samples by organ rather than by species. Organs differed in their degrees of expression variance within species and expression divergence between species. Variance was negatively correlated with expression breadth and protein interactivity, suggesting that pleiotropic constraints reduce gene expression variance within species. Variance was correlated with between‐species divergence, consistent with a pattern expected from stabilizing selection and neutral evolution. Using an expression PST approach, we identified genes differentially expressed between species and found 16 genes uniquely expressed in one of the species. For one of these, DPP7, uniquely expressed in collared flycatcher, the absence of expression in pied flycatcher could be associated with a ≈20‐kb deletion including 11 of 13 exons. This study of a young vertebrate speciation model system expands our knowledge of how gene expression evolves as natural populations become reproductively isolated.
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Affiliation(s)
- Severin Uebbing
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden
| | - Axel Künstner
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden
| | - Hannu Mäkinen
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden
| | - Niclas Backström
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden
| | - Paulina Bolivar
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden
| | - Reto Burri
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden
| | - Ludovic Dutoit
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden
| | - Carina F Mugal
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden
| | - Alexander Nater
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden
| | - Bronwen Aken
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, UK.,Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, UK
| | - Paul Flicek
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, UK
| | - Fergal J Martin
- European Molecular Biology Laboratory, European Bioinformatics Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, UK.,Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, UK
| | - Stephen M J Searle
- Wellcome Trust Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, UK
| | - Hans Ellegren
- Department of Evolutionary Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden
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24
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Mack KL, Campbell P, Nachman MW. Gene regulation and speciation in house mice. Genome Res 2016; 26:451-61. [PMID: 26833790 PMCID: PMC4817769 DOI: 10.1101/gr.195743.115] [Citation(s) in RCA: 69] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Accepted: 01/28/2016] [Indexed: 01/15/2023]
Abstract
One approach to understanding the process of speciation is to characterize the genetic architecture of post-zygotic isolation. As gene regulation requires interactions between loci, negative epistatic interactions between divergent regulatory elements might underlie hybrid incompatibilities and contribute to reproductive isolation. Here, we take advantage of a cross between house mouse subspecies, where hybrid dysfunction is largely unidirectional, to test several key predictions about regulatory divergence and reproductive isolation. Regulatory divergence between Mus musculus musculus and M. m. domesticus was characterized by studying allele-specific expression in fertile hybrid males using mRNA-sequencing of whole testes. We found extensive regulatory divergence between M. m. musculus and M. m. domesticus, largely attributable to cis-regulatory changes. When both cis and trans changes occurred, they were observed in opposition much more often than expected under a neutral model, providing strong evidence of widespread compensatory evolution. We also found evidence for lineage-specific positive selection on a subset of genes related to transcriptional regulation. Comparisons of fertile and sterile hybrid males identified a set of genes that were uniquely misexpressed in sterile individuals. Lastly, we discovered a nonrandom association between these genes and genes showing evidence of compensatory evolution, consistent with the idea that regulatory interactions might contribute to Dobzhansky-Muller incompatibilities and be important in speciation.
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Affiliation(s)
- Katya L Mack
- Museum of Vertebrate Zoology and Department of Integrative Biology, University of California, Berkeley, California 94720-3160, USA
| | - Polly Campbell
- Department of Integrative Biology, Oklahoma State University, Stillwater, Oklahoma 74078, USA
| | - Michael W Nachman
- Museum of Vertebrate Zoology and Department of Integrative Biology, University of California, Berkeley, California 94720-3160, USA
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25
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Simple Biophysical Model Predicts Faster Accumulation of Hybrid Incompatibilities in Small Populations Under Stabilizing Selection. Genetics 2015; 201:1525-37. [PMID: 26434721 PMCID: PMC4676520 DOI: 10.1534/genetics.115.181685] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Accepted: 09/23/2015] [Indexed: 01/07/2023] Open
Abstract
Speciation is fundamental to the process of generating the huge diversity of life on Earth. However, we are yet to have a clear understanding of its molecular-genetic basis. Here, we examine a computational model of reproductive isolation that explicitly incorporates a map from genotype to phenotype based on the biophysics of protein–DNA binding. In particular, we model the binding of a protein transcription factor to a DNA binding site and how their independent coevolution, in a stabilizing fitness landscape, of two allopatric lineages leads to incompatibilities. Complementing our previous coarse-grained theoretical results, our simulations give a new prediction for the monomorphic regime of evolution that smaller populations should develop incompatibilities more quickly. This arises as (1) smaller populations have a greater initial drift load, as there are more sequences that bind poorly than well, so fewer substitutions are needed to reach incompatible regions of phenotype space, and (2) slower divergence when the population size is larger than the inverse of discrete differences in fitness. Further, we find longer sequences develop incompatibilities more quickly at small population sizes, but more slowly at large population sizes. The biophysical model thus represents a robust mechanism of rapid reproductive isolation for small populations and large sequences that does not require peak shifts or positive selection. Finally, we show that the growth of DMIs with time is quadratic for small populations, agreeing with Orr’s model, but nonpower law for large populations, with a form consistent with our previous theoretical results.
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Khatri BS, Goldstein RA. A coarse-grained biophysical model of sequence evolution and the population size dependence of the speciation rate. J Theor Biol 2015; 378:56-64. [PMID: 25936759 PMCID: PMC4457359 DOI: 10.1016/j.jtbi.2015.04.027] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2014] [Revised: 02/20/2015] [Accepted: 04/20/2015] [Indexed: 11/29/2022]
Abstract
Speciation is fundamental to understanding the huge diversity of life on Earth. Although still controversial, empirical evidence suggests that the rate of speciation is larger for smaller populations. Here, we explore a biophysical model of speciation by developing a simple coarse-grained theory of transcription factor-DNA binding and how their co-evolution in two geographically isolated lineages leads to incompatibilities. To develop a tractable analytical theory, we derive a Smoluchowski equation for the dynamics of binding energy evolution that accounts for the fact that natural selection acts on phenotypes, but variation arises from mutations in sequences; the Smoluchowski equation includes selection due to both gradients in fitness and gradients in sequence entropy, which is the logarithm of the number of sequences that correspond to a particular binding energy. This simple consideration predicts that smaller populations develop incompatibilities more quickly in the weak mutation regime; this trend arises as sequence entropy poises smaller populations closer to incompatible regions of phenotype space. These results suggest a generic coarse-grained approach to evolutionary stochastic dynamics, allowing realistic modelling at the phenotypic level.
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Affiliation(s)
- Bhavin S Khatri
- The Francis Crick Institute, Mill Hill Laboratory, The Ridgeway, London NW7 1AA, UK; Division of Infection & Immunity, University College London, London WC1E 6BT, UK.
| | - Richard A Goldstein
- Division of Infection & Immunity, University College London, London WC1E 6BT, UK.
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Lindtke D, Buerkle CA. The genetic architecture of hybrid incompatibilities and their effect on barriers to introgression in secondary contact. Evolution 2015; 69:1987-2004. [DOI: 10.1111/evo.12725] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2015] [Accepted: 07/08/2015] [Indexed: 12/30/2022]
Affiliation(s)
- Dorothea Lindtke
- Department of Botany and Program in Ecology; University of Wyoming; Laramie Wyoming 82071
- Department of Animal and Plant Sciences; University of Sheffield; Sheffield S10 2TN United Kingdom
| | - C. Alex Buerkle
- Department of Botany and Program in Ecology; University of Wyoming; Laramie Wyoming 82071
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Abstract
Hybrids between species are often sterile or inviable. This form of reproductive isolation is thought to evolve via the accumulation of mutations that interact to reduce fitness when combined in hybrids. Mathematical formulations of this "Dobzhansky-Muller model" predict an accelerating buildup of hybrid incompatibilities with divergence time (the "snowball effect"). Although the Dobzhansky-Muller model is widely accepted, the snowball effect has only been tested in two species groups. We evaluated evidence for the snowball effect in the evolution of hybrid male sterility among subspecies of house mice, a recently diverged group that shows partial reproductive isolation. We compared the history of subspecies divergence with patterns of quantitative trait loci (QTL) detected in F2 intercrosses between two pairs of subspecies (Mus musculus domesticus with M. m. musculus and M. m. domesticus with M. m. castaneus). We used a recently developed phylogenetic comparative method to statistically measure the fit of these data to the snowball prediction. To apply this method, QTL were partitioned as either shared or unshared in the two crosses. A heuristic partitioning based on the overlap of QTL confidence intervals produced unambiguous support for the snowball effect. An alternative approach combining data among crosses favored the snowball effect for the autosomes, but a linear accumulation of incompatibilities for the X chromosome. Reasoning that the X chromosome analyses are complicated by low mapping resolution, we conclude that hybrid male sterility loci have snowballed in house mice. Our study illustrates the power of comparative genetic mapping for understanding mechanisms of speciation.
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Hybrid incompatibility despite pleiotropic constraint in a sequence-based bioenergetic model of transcription factor binding. Genetics 2014; 198:1645-54. [PMID: 25313130 DOI: 10.1534/genetics.114.171397] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Hybrid incompatibility can result from gene misregulation produced by divergence in trans-acting regulatory factors and their cis-regulatory targets. However, change in trans-acting factors may be constrained by pleiotropy, which would in turn limit the evolution of incompatibility. We employed a mechanistically explicit bioenergetic model of gene expression wherein parameter combinations (number of transcription factor molecules, energetic properties of binding to the regulatory site, and genomic background size) determine the shape of the genotype-phenotype (G-P) map, and interacting allelic variants of mutable cis and trans sites determine the phenotype along that map. Misregulation occurs when the phenotype differs from its optimal value. We simulated a pleiotropic regulatory pathway involving a positively selected and a conserved trait regulated by a shared transcription factor (TF), with two populations evolving in parallel. Pleiotropic constraints shifted evolution in the positively selected trait to its cis-regulatory locus. We nevertheless found that the TF genotypes often evolved, accompanied by compensatory evolution in the conserved trait, and both traits contributed to hybrid misregulation. Compensatory evolution resulted in "developmental system drift," whereby the regulatory basis of the conserved phenotype changed although the phenotype itself did not. Pleiotropic constraints became stronger and in some cases prohibitive when the bioenergetic properties of the molecular interaction produced a G-P map that was too steep. Likewise, compensatory evolution slowed and hybrid misregulation was not evident when the G-P map was too shallow. A broad pleiotropic "sweet spot" nevertheless existed where evolutionary constraints were moderate to weak, permitting substantial hybrid misregulation in both traits. None of these pleiotropic constraints manifested when the TF contained nonrecombining domains independently regulating the respective traits.
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