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Yamabe T, Kajitani R, Toyoda A, Itoh T. Chromosomal-level Genome Assembly of the Coffee Bee Hawk Moth Reveals the Evolution of Chromosomes and the Molecular Basis of Distinct Phenotypes. Genome Biol Evol 2023; 15:evad141. [PMID: 37494061 PMCID: PMC10476703 DOI: 10.1093/gbe/evad141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Revised: 07/20/2023] [Accepted: 07/22/2023] [Indexed: 07/27/2023] Open
Abstract
Cephonodes hylas, the coffee bee hawk moth is a hawk moth species with unique characteristics, such as larvae feeding on gardenia, overcoming the toxicity of its iridoid glycosides, diurnal adults, and transparent wings. Although C. hylas is a fascinating model for molecular biological research, genome sequence analysis-based genetic approaches to elucidate these peculiarities have not yet been undertaken. We successfully achieved de novo genome assembly at the chromosome level of C. hylas comparable to the Lepidoptera model organism, silkworm. Additionally, 16,854 protein-coding genes were annotated, and the constructed genome sequence and annotated genes were of the highest quality BUSCO completion compared to closely related species. Comparative genome analysis revealed the process of chromosomal evolution from the Bombycoidea ancestral (n = 31) genome and changes in turnover at the chromosome level associated with chromosomal fusion events, such as the rate of repetitive sequence insertion. These analyses were only possible because the genome was constructed at the chromosome level. Additionally, increased the nonsynonymous/synonymous rate (dN/dS) ratios were observed in multiple photoreceptor-related genes that were strongly associated with the acquisition of diurnal activity. Furthermore, tandemly duplicated expanded genes containing many digestive and other enzymes and larval midgut-specific expression were also confirmed. These genes may be involved in the metabolism of genipin, a toxin found in gardenias. Using the genome sequence of C. hylas determined at the chromosome level, we have successfully identified new insights into the chromosomal evolution of Bombycoidea, as well as the relationship between the genome sequence and its characteristic traits.
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Affiliation(s)
- Takahiro Yamabe
- School of Life Science and Technology, Tokyo Institute of Technology, Tokyo, Japan
| | - Rei Kajitani
- School of Life Science and Technology, Tokyo Institute of Technology, Tokyo, Japan
| | - Atsushi Toyoda
- Comparative Genomics Laboratory, National Institute of Genetics, Shizuoka, Japan
- Advanced Genomics Center, National Institute of Genetics, Shizuoka, Japan
| | - Takehiko Itoh
- School of Life Science and Technology, Tokyo Institute of Technology, Tokyo, Japan
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2
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Wang Y, Zhang H, Xian W, Iwasaki W. Chromosome genome assembly and annotation of the spiny red gurnard (Chelidonichthys spinosus). Sci Data 2023; 10:443. [PMID: 37438353 DOI: 10.1038/s41597-023-02357-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Accepted: 06/30/2023] [Indexed: 07/14/2023] Open
Abstract
Chelidonichthys spinosus, a secondary economic fish, is increasingly being exploited and valued in China. However, overfishing has led to it being recognized as one of the most depleted marine species in China. In this study, we generated a chromosome-level genome of C. spinosus using PacBio, Illumina, and Hi-C sequencing data. Ultimately, we assembled a 624.7 Mb genome of C. spinosus, with a contig N50 of 13.77 Mb and scaffold N50 of 28.11 Mb. We further anchored and oriented the assembled sequences onto 24 pseudo-chromosomes using Hi-C techniques. In total, 25,358 protein-coding genes were predicted, of which 24,072 (94.93%) genes were functionally annotated. The dot plot reveals a prominent co-linearity between C. spinosus and Cyclopterus lumpus, indicating a remarkably close phylogenetic relationship between these two species. The assembled genome sequences provide valuable information for elucidating the genetic adaptation and potential molecular basis of C. spinosus. They also have the potential to provide insight into the evolutionary investigation of teleost fish and vertebrates.
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Affiliation(s)
- Yibang Wang
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Hui Zhang
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.
- University of Chinese Academy of Sciences, Beijing, China.
| | - Weiwei Xian
- CAS Key Laboratory of Marine Ecology and Environmental Sciences, Institute of Oceanology, Chinese Academy of Sciences, Qingdao, China.
| | - Wataru Iwasaki
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, the University of Tokyo, Kashiwa, Japan
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3
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Zhou W, Furey NM, Soisook P, Thong VD, Lim BK, Rossiter SJ, Mao X. Diversification and introgression in four chromosomal taxa of the Pearson's horseshoe bat (Rhinolophus pearsoni) group. Mol Phylogenet Evol 2023; 183:107784. [PMID: 37040825 DOI: 10.1016/j.ympev.2023.107784] [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: 12/09/2022] [Revised: 03/11/2023] [Accepted: 04/07/2023] [Indexed: 04/13/2023]
Abstract
Chromosomal variation among closely related taxa is common in both plants and animals, and can reduce rates of introgression as well as promote reproductive isolation and speciation. In mammals, studies relating introgression to chromosomal variation have tended to focus on a few model systems and typically characterized levels of introgression using small numbers of loci. Here we took a genome-wide approach to examine how introgression rates vary among four closely related horseshoe bats (Rhinolophus pearsoni group) that possess different diploid chromosome numbers (2n = 42, 44, 46, and 60) resulting from Robertsonian (Rb) changes (fissions/fusions). Using a sequence capture we obtained orthologous loci for thousands of nuclear loci, as well as mitogenomes, and performed phylogenetic and population genetic analyses. We found that the taxon with 2n = 60 was the first to diverge in this group, and that the relationships among the three other taxa (2n = 42, 44 and 46) showed discordance across our different analyses. Our results revealed signatures of multiple ancient introgression events between the four taxa, with evidence of mitonuclar discordance in phylogenetic trees and reticulation events in their evolutionary history. Despite this, we found no evidence of recent and/or ongoing introgression between taxa. Overall, our results indicate that the effects of Rb changes on the reduction of introgression are complicated and that these may contribute to reproductive isolation and speciation in concert with other factors (e.g. phenotypic and genic divergence).
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Affiliation(s)
- Weiwei Zhou
- School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200062, China
| | - Neil M Furey
- Fauna & Flora International (Cambodia), PO Box 1380, No. 19, Street 360, Boeng Keng Kong 1, Phnom Penh 12000, Cambodia
| | - Pipat Soisook
- Princess Maha Chakri Sirindhorn Natural History Museum, Prince of Songkla University, Hat Yai, Songkhla 90110, Thailand
| | - Vu D Thong
- Institute of Ecology and Biological Resources, Vietnam Academy of Science and Technology (VAST), 18 Hoang Quoc Viet Road, Cau Giay District, Hanoi, Viet Nam; Graduate University of Science and Technology, VAST, Viet Nam
| | - Burton K Lim
- Department of Natural History, Royal Ontario Museum, Toronto, Ontario M5S 2C6, Canada
| | - Stephen J Rossiter
- School of Biological and Behavioural Sciences, Queen Mary University of London, London E1 4NS, UK.
| | - Xiuguang Mao
- School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200062, China.
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4
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Wucherpfennig JI, Howes TR, Au JN, Au EH, Roberts Kingman GA, Brady SD, Herbert AL, Reimchen TE, Bell MA, Lowe CB, Dalziel AC, Kingsley DM. Evolution of stickleback spines through independent cis-regulatory changes at HOXDB. Nat Ecol Evol 2022; 6:1537-1552. [PMID: 36050398 PMCID: PMC9525239 DOI: 10.1038/s41559-022-01855-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2022] [Accepted: 07/19/2022] [Indexed: 11/10/2022]
Abstract
Understanding the mechanisms leading to new traits or additional features in organisms is a fundamental goal of evolutionary biology. We show that HOXDB regulatory changes have been used repeatedly in different fish genera to alter the length and number of the prominent dorsal spines used to classify stickleback species. In Gasterosteus aculeatus (typically 'three-spine sticklebacks'), a variant HOXDB allele is genetically linked to shortening an existing spine and adding an additional spine. In Apeltes quadracus (typically 'four-spine sticklebacks'), a variant HOXDB allele is associated with lengthening a spine and adding an additional spine in natural populations. The variant alleles alter the same non-coding enhancer region in the HOXDB locus but do so by diverse mechanisms, including single-nucleotide polymorphisms, deletions and transposable element insertions. The independent regulatory changes are linked to anterior expansion or contraction of HOXDB expression. We propose that associated changes in spine lengths and numbers are partial identity transformations in a repeating skeletal series that forms major defensive structures in fish. Our findings support the long-standing hypothesis that natural Hox gene variation underlies key patterning changes in wild populations and illustrate how different mutational mechanisms affecting the same region may produce opposite gene expression changes with similar phenotypic outcomes.
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Affiliation(s)
- Julia I Wucherpfennig
- Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Timothy R Howes
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Jessica N Au
- Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Eric H Au
- Department of Molecular Genetics and Microbiology, Duke University School of Medicine, Durham, NC, USA
| | | | - Shannon D Brady
- Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Amy L Herbert
- Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA, USA
| | - Thomas E Reimchen
- Department of Biology, University of Victoria, Victoria, British Columbia, Canada
| | - Michael A Bell
- University of California Museum of Paleontology, University of California, Berkeley, CA, USA
| | - Craig B Lowe
- Department of Molecular Genetics and Microbiology, Duke University School of Medicine, Durham, NC, USA
| | - Anne C Dalziel
- Department of Biology, Saint Mary's University, Halifax, Nova Scotia, Canada
| | - David M Kingsley
- Department of Developmental Biology, Stanford University School of Medicine, Stanford, CA, USA.
- Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, CA, USA.
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5
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Jeffries DL, Mee JA, Peichel CL. Identification of a candidate sex determination gene in Culaea inconstans suggests convergent recruitment of an Amh duplicate in two lineages of stickleback. J Evol Biol 2022; 35:1683-1695. [PMID: 35816592 PMCID: PMC10083969 DOI: 10.1111/jeb.14034] [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: 01/07/2022] [Revised: 04/07/2022] [Accepted: 05/19/2022] [Indexed: 11/29/2022]
Abstract
Sex chromosomes vary greatly in their age and levels of differentiation across the tree of life. This variation is largely due to the rates of sex chromosome turnover in different lineages; however, we still lack an explanation for why sex chromosomes are so conserved in some lineages (e.g. mammals, birds) but so labile in others (e.g. teleosts, amphibians). To identify general mechanisms driving transitions in sex determination systems or forces which favour their conservation, we first require empirical data on sex chromosome systems from multiple lineages. Stickleback fishes are a valuable model lineage for the study of sex chromosome evolution due to variation in sex chromosome systems between closely-related species. Here, we identify the sex chromosome and a strong candidate for the master sex determination gene in the brook stickleback, Culaea inconstans. Using whole-genome sequencing of wild-caught samples and a lab cross, we identify AmhY, a male specific duplication of the gene Amh, as the candidate master sex determination gene. AmhY resides on Chromosome 20 in C. inconstans and is likely a recent duplication, as both AmhY and the sex-linked region of Chromosome 20 show little sequence divergence. Importantly, this duplicate AmhY represents the second independent duplication and recruitment of Amh as the sex determination gene in stickleback and the eighth example known across teleosts. We discuss this convergence in the context of sex chromosome turnovers and the role that the Amh/AmhrII pathway, which is crucial for sex determination, may play in the evolution of sex chromosomes in teleosts.
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Affiliation(s)
- Daniel L Jeffries
- Division of Evolutionary Ecology, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland
| | - Jonathan A Mee
- Department of Biology, Mount Royal University, Calgary, Alberta, Canada
| | - Catherine L Peichel
- Division of Evolutionary Ecology, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland
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Roesti M, Gilbert KJ, Samuk K. Chromosomal inversions can limit adaptation to new environments. Mol Ecol 2022; 31:4435-4439. [PMID: 35810344 DOI: 10.1111/mec.16609] [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: 05/03/2022] [Revised: 07/04/2022] [Accepted: 07/05/2022] [Indexed: 11/29/2022]
Abstract
Chromosomal inversions are often thought to facilitate local adaptation and population divergence because they can link multiple adaptive alleles into non-recombining genomic blocks. Selection should thus be more efficient in driving inversion-linked adaptive alleles to high frequency in a population, particularly in the face of maladaptive gene flow. But what if ecological conditions and hence selection on inversion-linked alleles change? Reduced recombination within inversions could then constrain the formation of optimal combinations of pre-existing alleles under these new ecological conditions. Here, we outline this idea of inversions limiting adaptation and divergence when ecological conditions change across time or space. We reason and use simulations to illustrate that the benefit of inversions for local adaptation and divergence under one set of ecological conditions can come with a concomitant constraint for adaptation to novel sets of ecological conditions. This limitation of inversions to adaptation may contribute to the maintenance of polymorphism within species.
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Affiliation(s)
- Marius Roesti
- Division of Evolutionary Ecology, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland
| | | | - Kieran Samuk
- Department of Evolution, Ecology, and Organismal Biology, University of California, Riverside, California, USA
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7
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Lysak MA. Celebrating Mendel, McClintock, and Darlington: On end-to-end chromosome fusions and nested chromosome fusions. THE PLANT CELL 2022; 34:2475-2491. [PMID: 35441689 PMCID: PMC9252491 DOI: 10.1093/plcell/koac116] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2022] [Accepted: 04/13/2022] [Indexed: 05/04/2023]
Abstract
The evolution of eukaryotic genomes is accompanied by fluctuations in chromosome number, reflecting cycles of chromosome number increase (polyploidy and centric fissions) and decrease (chromosome fusions). Although all chromosome fusions result from DNA recombination between two or more nonhomologous chromosomes, several mechanisms of descending dysploidy are exploited by eukaryotes to reduce their chromosome number. Genome sequencing and comparative genomics have accelerated the identification of inter-genome chromosome collinearity and gross chromosomal rearrangements and have shown that end-to-end chromosome fusions (EEFs) and nested chromosome fusions (NCFs) may have played a more important role in the evolution of eukaryotic karyotypes than previously thought. The present review aims to summarize the limited knowledge on the origin, frequency, and evolutionary implications of EEF and NCF events in eukaryotes and especially in land plants. The interactions between nonhomologous chromosomes in interphase nuclei and chromosome (mis)pairing during meiosis are examined for their potential importance in the origin of EEFs and NCFs. The remaining open questions that need to be addressed are discussed.
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Affiliation(s)
- Martin A Lysak
- CEITEC—Central European Institute of Technology, Masaryk University, Brno, CZ-625 00, Czech Republic
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8
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Aguirre WE, Reid K, Rivera J, Heins DC, Veeramah KR, Bell MA. Freshwater Colonization, Adaptation, and Genomic Divergence in Threespine Stickleback. Integr Comp Biol 2022; 62:388-405. [PMID: 35660873 PMCID: PMC9405723 DOI: 10.1093/icb/icac071] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Revised: 04/25/2022] [Accepted: 05/24/2022] [Indexed: 11/14/2022] Open
Abstract
The Threespine Stickleback is ancestrally a marine fish, but many marine populations breed in fresh water (i.e., are anadromous), facilitating their colonization of isolated freshwater habitats a few years after they form. Repeated adaptation to fresh water during at least 10 My and continuing today has led to Threespine Stickleback becoming a premier system to study rapid adaptation. Anadromous and freshwater stickleback breed in sympatry and may hybridize, resulting in introgression of freshwater-adaptive alleles into anadromous populations, where they are maintained at low frequencies as ancient standing genetic variation. Anadromous stickleback have accumulated hundreds of freshwater-adaptive alleles that are disbursed as few loci per marine individual and provide the basis for adaptation when they colonize fresh water. Recent whole-lake experiments in lakes around Cook Inlet, Alaska have revealed how astonishingly rapid and repeatable this process is, with the frequency of 40% of the identified freshwater-adaptive alleles increasing from negligible (∼1%) in the marine founder to ≥50% within ten generations in fresh water, and freshwater phenotypes evolving accordingly. These high rates of genomic and phenotypic evolution imply very intense directional selection on phenotypes of heterozygotes. Sexual recombination rapidly assembles freshwater-adaptive alleles that originated in different founders into multilocus freshwater haplotypes, and regions important for adaptation to freshwater have suppressed recombination that keeps advantageous alleles linked within large haploblocks. These large haploblocks are also older and appear to have accumulated linked advantageous mutations. The contemporary evolution of Threespine Stickleback has provided broadly applicable insights into the mechanisms that facilitate rapid adaptation.
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Affiliation(s)
- Windsor E Aguirre
- Department of Biological Sciences, DePaul University, Chicago, IL 60614, USA
| | - Kerry Reid
- School of Biological Sciences, Area of Ecology and Biodiversity, University of Hong Kong, Hong Kong, SAR, China.,Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY 11794, USA
| | - Jessica Rivera
- Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland
| | - David C Heins
- Department of Ecology and Evolutionary Biology, Tulane University, New Orleans 70118, USA
| | - Krishna R Veeramah
- Department of Ecology and Evolution, Stony Brook University, Stony Brook, NY 11794, USA
| | - Michael A Bell
- University of California Museum of Paleontology, University of California, Berkeley, CA 94720, USA
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Li Q, Lindtke D, Rodríguez-Ramírez C, Kakioka R, Takahashi H, Toyoda A, Kitano J, Ehrlich RL, Chang Mell J, Yeaman S. Local Adaptation and the Evolution of Genome Architecture in Threespine Stickleback. Genome Biol Evol 2022; 14:6589818. [PMID: 35594844 PMCID: PMC9178229 DOI: 10.1093/gbe/evac075] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/16/2022] [Indexed: 12/11/2022] Open
Abstract
Theory predicts that local adaptation should favor the evolution of a concentrated genetic architecture, where the alleles driving adaptive divergence are tightly clustered on chromosomes. Adaptation to marine versus freshwater environments in threespine stickleback has resulted in an architecture that seems consistent with this prediction: divergence among populations is mainly driven by a few genomic regions harboring multiple quantitative trait loci for environmentally adapted traits, as well as candidate genes with well-established phenotypic effects. One theory for the evolution of these "genomic islands" is that rearrangements remodel the genome to bring causal loci into tight proximity, but this has not been studied explicitly. We tested this theory using synteny analysis to identify micro- and macro-rearrangements in the stickleback genome and assess their potential involvement in the evolution of genomic islands. To identify rearrangements, we conducted a de novo assembly of the closely related tubesnout (Aulorhyncus flavidus) genome and compared this to the genomes of threespine stickleback and two other closely related species. We found that small rearrangements, within-chromosome duplications, and lineage-specific genes (LSGs) were enriched around genomic islands, and that all three chromosomes harboring large genomic islands have experienced macro-rearrangements. We also found that duplicates and micro-rearrangements are 9.9× and 2.9× more likely to involve genes differentially expressed between marine and freshwater genotypes. While not conclusive, these results are consistent with the explanation that strong divergent selection on candidate genes drove the recruitment of rearrangements to yield clusters of locally adaptive loci.
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Affiliation(s)
- Qiushi Li
- Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Canada T2N 1N4
| | - Dorothea Lindtke
- Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Canada T2N 1N4
| | - Carlos Rodríguez-Ramírez
- Division of Evolutionary Ecology, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland
| | - Ryo Kakioka
- Tropical Biosphere Research Center, University of the Ryukyus, Nishihara, Nakagami-gun, Okinawa 903-0213, Japan
| | - Hiroshi Takahashi
- National Fisheries University, 2-7-1 Nagata-honmachi, Shimonoseki, Yamaguchi 759-6595, Japan
| | - Atsushi Toyoda
- Comparative Genomics Laboratory, National Institute of Genetics, Mishima, Shizuoka 411-8540, Japan
| | - Jun Kitano
- Ecological Genetics Laboratory, National Institute of Genetics, Mishima, Shizuoka 411-8540, Japan
| | - Rachel L Ehrlich
- Department of Microbiology & Immunology, Drexel University College of Medicine, Philadelphia 19102, PA, USA
| | - Joshua Chang Mell
- Department of Microbiology & Immunology, Drexel University College of Medicine, Philadelphia 19102, PA, USA
| | - Sam Yeaman
- Department of Biological Sciences, University of Calgary, 2500 University Drive NW, Calgary, Canada T2N 1N4
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Recurrent chromosome reshuffling and the evolution of neo-sex chromosomes in parrots. Nat Commun 2022; 13:944. [PMID: 35177601 PMCID: PMC8854603 DOI: 10.1038/s41467-022-28585-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2021] [Accepted: 01/26/2022] [Indexed: 12/13/2022] Open
Abstract
The karyotype of most birds has remained considerably stable during more than 100 million years’ evolution, except for some groups, such as parrots. The evolutionary processes and underlying genetic mechanism of chromosomal rearrangements in parrots, however, are poorly understood. Here, using chromosome-level assemblies of four parrot genomes, we uncover frequent chromosome fusions and fissions, with most of them occurring independently among lineages. The increased activities of chromosomal rearrangements in parrots are likely associated with parrot-specific loss of two genes, ALC1 and PARP3, that have known functions in the repair of double-strand breaks and maintenance of genome stability. We further find that the fusion of the ZW sex chromosomes and chromosome 11 has created a pair of neo-sex chromosomes in the ancestor of parrots, and the chromosome 25 has been further added to the sex chromosomes in monk parakeet. Together, the combination of our genomic and cytogenetic analyses characterizes the complex evolutionary history of chromosomal rearrangements and sex chromosomes in parrots. Parrots have undergone substantial karyotype evolution compared to most other birds. Here, Huang et al. analyze chromosome-level genome assemblies for four parrot species and elucidate the complex evolutionary history of parrot chromosomes.
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