1
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Molecular evidence for a single origin of ultrafiltration-based excretory organs. Curr Biol 2021; 31:3629-3638.e2. [PMID: 34166606 DOI: 10.1016/j.cub.2021.05.057] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2021] [Revised: 04/14/2021] [Accepted: 05/26/2021] [Indexed: 01/14/2023]
Abstract
Excretion is an essential physiological process, carried out by all living organisms, regardless of their size or complexity.1-3 Both protostomes (e.g., flies and flatworms) and deuterostomes (e.g., humans and sea urchins) possess specialized excretory organs serving that purpose. Those organs exhibit an astonishing diversity, ranging from units composed of just few distinct cells (e.g., protonephridia) to complex structures, built by millions of cells of multiple types with divergent morphology and function (e.g., vertebrate kidneys).4,5 Although some molecular similarities between the development of kidneys of vertebrates and the regeneration of the protonephridia of flatworms have been reported,6,7 the molecular underpinnings of the development of excretory organs have never been systematically studied in a comparative context.4 Here, we show that a set of transcription factors (eya, six1/2, pou3, sall, lhx1/5, and osr) and structural proteins (nephrin, kirre, and zo1) is expressed in the excretory organs of a phoronid, brachiopod, annelid, onychophoran, priapulid, and hemichordate that represent major protostome lineages and non-vertebrate deuterostomes. We demonstrate that the molecular similarity observed in the vertebrate kidney and flatworm protonephridia6,7 is also seen in the developing excretory organs of those animals. Our results show that all types of ultrafiltration-based excretory organs are patterned by a conserved set of developmental genes, an observation that supports their homology. We propose that the last common ancestor of protostomes and deuterostomes already possessed an ultrafiltration-based organ that later gave rise to the vast diversity of extant excretory organs, including both proto- and metanephridia.
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2
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Eckelbarger KJ, Hodgson AN. Invertebrate oogenesis – a review and synthesis: comparative ovarian morphology, accessory cell function and the origins of yolk precursors. INVERTEBR REPROD DEV 2021. [DOI: 10.1080/07924259.2021.1927861] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Kevin J. Eckelbarger
- Darling Marine Center, School of Marine Sciences, The University of Maine, Walpole, Maine, U.S.A
| | - Alan N. Hodgson
- Department of Zoology and Entomology, Rhodes University, Grahamstown, South Africa
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3
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Heger P, Zheng W, Rottmann A, Panfilio KA, Wiehe T. The genetic factors of bilaterian evolution. eLife 2020; 9:e45530. [PMID: 32672535 PMCID: PMC7535936 DOI: 10.7554/elife.45530] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2019] [Accepted: 07/03/2020] [Indexed: 12/13/2022] Open
Abstract
The Cambrian explosion was a unique animal radiation ~540 million years ago that produced the full range of body plans across bilaterians. The genetic mechanisms underlying these events are unknown, leaving a fundamental question in evolutionary biology unanswered. Using large-scale comparative genomics and advanced orthology evaluation techniques, we identified 157 bilaterian-specific genes. They include the entire Nodal pathway, a key regulator of mesoderm development and left-right axis specification; components for nervous system development, including a suite of G-protein-coupled receptors that control physiology and behaviour, the Robo-Slit midline repulsion system, and the neurotrophin signalling system; a high number of zinc finger transcription factors; and novel factors that previously escaped attention. Contradicting the current view, our study reveals that genes with bilaterian origin are robustly associated with key features in extant bilaterians, suggesting a causal relationship.
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Affiliation(s)
- Peter Heger
- Institute for Genetics, Cologne Biocenter, University of CologneCologneGermany
| | - Wen Zheng
- Institute for Genetics, Cologne Biocenter, University of CologneCologneGermany
| | - Anna Rottmann
- Institute for Genetics, Cologne Biocenter, University of CologneCologneGermany
| | - Kristen A Panfilio
- Institute for Zoology: Developmental Biology, Cologne Biocenter, University of CologneCologneGermany
- School of Life Sciences, University of Warwick, Gibbet Hill CampusCoventryUnited Kingdom
| | - Thomas Wiehe
- Institute for Genetics, Cologne Biocenter, University of CologneCologneGermany
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4
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Fields C, Levin M. Does regeneration recapitulate phylogeny? Planaria as a model of body-axis specification in ancestral eumetazoa. Commun Integr Biol 2020; 13:27-38. [PMID: 32128026 PMCID: PMC7039665 DOI: 10.1080/19420889.2020.1729601] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2019] [Revised: 02/07/2020] [Accepted: 02/09/2020] [Indexed: 12/31/2022] Open
Abstract
Metazoan body plans combine well-defined primary, secondary, and in many bilaterians, tertiary body axes with structural asymmetries at multiple scales. Despite decades of study, how axis-defining symmetries and system-defining asymmetries co-emerge during both evolution and development remain open questions. Regeneration studies in asexual planaria have demonstrated an array of viable forms with symmetrized and, in some cases, duplicated body axes. We suggest that such forms may point toward an ancestral eumetazoan form with characteristics of both cnidarians and placazoa.
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Affiliation(s)
| | - Michael Levin
- Allen Discovery Center, Tufts University, Medford, MA, USA
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5
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Buckland-Nicks JA, Fields AH. Genesis and structure of eusperm and parasperm of Plicopurpura patula in relation to phylogeny of Neogastropoda: proteomics of parasperm suggests role in paternity assurance. INVERTEBR REPROD DEV 2020. [DOI: 10.1080/07924259.2019.1695681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
| | - Angela H. Fields
- Department of Biological and Chemical Sciences, University of West Indies, Bridgetown, Barbados
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6
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Andrikou C, Thiel D, Ruiz-Santiesteban JA, Hejnol A. Active mode of excretion across digestive tissues predates the origin of excretory organs. PLoS Biol 2019; 17:e3000408. [PMID: 31356592 PMCID: PMC6687202 DOI: 10.1371/journal.pbio.3000408] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2019] [Revised: 08/08/2019] [Accepted: 07/12/2019] [Indexed: 11/21/2022] Open
Abstract
Most bilaterian animals excrete toxic metabolites through specialized organs, such as nephridia and kidneys, which share morphological and functional correspondences. In contrast, excretion in non-nephrozoans is largely unknown, and therefore the reconstruction of ancestral excretory mechanisms is problematic. Here, we investigated the excretory mode of members of the Xenacoelomorpha, the sister group to Nephrozoa, and Cnidaria, the sister group to Bilateria. By combining gene expression, inhibitor experiments, and exposure to varying environmental ammonia conditions, we show that both Xenacoelomorpha and Cnidaria are able to excrete across digestive-associated tissues. However, although the cnidarian Nematostella vectensis seems to use diffusion as its main excretory mode, the two xenacoelomorphs use both active transport and diffusion mechanisms. Based on these results, we propose that digestive-associated tissues functioned as excretory sites before the evolution of specialized organs in nephrozoans. We conclude that the emergence of a compact, multiple-layered bilaterian body plan necessitated the evolution of active transport mechanisms, which were later recruited into the specialized excretory organs.
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Affiliation(s)
- Carmen Andrikou
- Sars International Centre for Marine Molecular Biology, University of Bergen, Bergen, Norway
| | - Daniel Thiel
- Sars International Centre for Marine Molecular Biology, University of Bergen, Bergen, Norway
| | | | - Andreas Hejnol
- Sars International Centre for Marine Molecular Biology, University of Bergen, Bergen, Norway
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7
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Marlétaz F. Zoology: Worming into the Origin of Bilaterians. Curr Biol 2019; 29:R577-R579. [DOI: 10.1016/j.cub.2019.05.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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8
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Planarian regeneration between 1960s and 1990s: From skilful baffled ancestors to bold integrative descendants. A personal account. Semin Cell Dev Biol 2019; 87:3-12. [DOI: 10.1016/j.semcdb.2018.04.011] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2018] [Revised: 04/13/2018] [Accepted: 04/25/2018] [Indexed: 12/11/2022]
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9
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Buckland-Nicks J, Lundin K, Wallberg A. The sperm of Xenacoelomorpha revisited: implications for the evolution of early bilaterians. ZOOMORPHOLOGY 2018. [DOI: 10.1007/s00435-018-0425-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
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10
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Griffith OW, Wagner GP. The placenta as a model for understanding the origin and evolution of vertebrate organs. Nat Ecol Evol 2017; 1:72. [DOI: 10.1038/s41559-017-0072] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Accepted: 01/06/2017] [Indexed: 12/19/2022]
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11
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Rosa MT, Oliveira DS, Loreto EL. Characterization of the first mitochondrial genome of a catenulid flatworm:Stenostomum leucops(Platyhelminthes). J ZOOL SYST EVOL RES 2017. [DOI: 10.1111/jzs.12164] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
| | - Daniel S. Oliveira
- Curso Ciências Biológicas; Univ. Fed. de Santa Maria (UFSM); Santa Maria Brazil
| | - Elgion L.S. Loreto
- Department of Biochemistry and Molecular Biology; CCNE; Univ. Fed. de Santa Maria; Santa Maria Brazil
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12
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Affiliation(s)
- Gonzalo Giribet
- Museum of Comparative Zoology & Department of Organismic and Evolutionary Biology Harvard University 26 Oxford Street Cambridge MA 02138 USA
- Department of Life Sciences The Natural History Museum Cromwell Road London SW7 5BD UK
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13
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Arroyo AS, López-Escardó D, de Vargas C, Ruiz-Trillo I. Hidden diversity of Acoelomorpha revealed through metabarcoding. Biol Lett 2016; 12:rsbl.2016.0674. [PMID: 27677819 PMCID: PMC5046940 DOI: 10.1098/rsbl.2016.0674] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Accepted: 09/06/2016] [Indexed: 01/29/2023] Open
Abstract
Animals with bilateral symmetry comprise the majority of the described species within Metazoa. However, the nature of the first bilaterian animal remains unknown. As most recent molecular phylogenies point to Xenacoelomorpha as the sister group to the rest of Bilateria, understanding their biology, ecology and diversity is key to reconstructing the nature of the last common bilaterian ancestor (Urbilateria). To date, sampling efforts have focused mainly on coastal areas, leaving potential gaps in our understanding of the full diversity of xenacoelomorphs. We therefore analysed 18S rDNA metabarcoding data from three marine projects covering benthic and pelagic habitats worldwide. Our results show that acoels have a greater richness in planktonic environments than previously described. Interestingly, we also identified a putative novel clade of acoels in the deep benthos that branches as sister group to the rest of Acoela, thus representing the earliest-branching acoel clade. Our data highlight deep-sea environments as an ideal habitat to sample acoels with key phylogenetic positions, which might be useful for reconstructing the early evolution of Bilateria.
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Affiliation(s)
- Alicia S Arroyo
- Institut de Biologia Evolutiva (CSIC-Universitat Pompeu Fabra), Passeig Marítim de la Barceloneta, 37-49, 08003 Barcelona, Spain
| | - David López-Escardó
- Institut de Biologia Evolutiva (CSIC-Universitat Pompeu Fabra), Passeig Marítim de la Barceloneta, 37-49, 08003 Barcelona, Spain
| | - Colomban de Vargas
- CNRS, UMR 7144, Station Biologique de Roscoff, Place Georges Teissier, 29680 Roscoff, France Sorbonne Universités, Université Pierre et Marie Curie (UPMC) Paris 06, UMR 7144, Station Biologique de Roscoff, Place Georges Teissier, 29680 Roscoff, France
| | - Iñaki Ruiz-Trillo
- Institut de Biologia Evolutiva (CSIC-Universitat Pompeu Fabra), Passeig Marítim de la Barceloneta, 37-49, 08003 Barcelona, Spain Departament de Genètica, Microbiologia i Estadística, Universitat de Barcelona, Avinguda Diagonal 643, 08028 Barcelona, Spain ICREA, Pg. Lluís Companys 23, 08010 Barcelona, Spain
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14
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Cannon JT, Vellutini BC, Smith J, Ronquist F, Jondelius U, Hejnol A. Xenacoelomorpha is the sister group to Nephrozoa. Nature 2016; 530:89-93. [PMID: 26842059 DOI: 10.1038/nature16520] [Citation(s) in RCA: 197] [Impact Index Per Article: 24.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2015] [Accepted: 12/07/2015] [Indexed: 01/06/2023]
Abstract
The position of Xenacoelomorpha in the tree of life remains a major unresolved question in the study of deep animal relationships. Xenacoelomorpha, comprising Acoela, Nemertodermatida, and Xenoturbella, are bilaterally symmetrical marine worms that lack several features common to most other bilaterians, for example an anus, nephridia, and a circulatory system. Two conflicting hypotheses are under debate: Xenacoelomorpha is the sister group to all remaining Bilateria (= Nephrozoa, namely protostomes and deuterostomes) or is a clade inside Deuterostomia. Thus, determining the phylogenetic position of this clade is pivotal for understanding the early evolution of bilaterian features, or as a case of drastic secondary loss of complexity. Here we show robust phylogenomic support for Xenacoelomorpha as the sister taxon of Nephrozoa. Our phylogenetic analyses, based on 11 novel xenacoelomorph transcriptomes and using different models of evolution under maximum likelihood and Bayesian inference analyses, strongly corroborate this result. Rigorous testing of 25 experimental data sets designed to exclude data partitions and taxa potentially prone to reconstruction biases indicates that long-branch attraction, saturation, and missing data do not influence these results. The sister group relationship between Nephrozoa and Xenacoelomorpha supported by our phylogenomic analyses implies that the last common ancestor of bilaterians was probably a benthic, ciliated acoelomate worm with a single opening into an epithelial gut, and that excretory organs, coelomic cavities, and nerve cords evolved after xenacoelomorphs separated from the stem lineage of Nephrozoa.
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Affiliation(s)
| | - Bruno Cossermelli Vellutini
- Sars International Centre for Marine Molecular Biology, University of Bergen, Thormøhlensgate 55, 5008 Bergen, Norway
| | - Julian Smith
- Department of Biology, Winthrop University, 701 Oakland Avenue, Rock Hill, South Carolina 29733, USA
| | - Fredrik Ronquist
- Naturhistoriska Riksmuseet, PO Box 50007, SE-104 05 Stockholm, Sweden
| | - Ulf Jondelius
- Naturhistoriska Riksmuseet, PO Box 50007, SE-104 05 Stockholm, Sweden
| | - Andreas Hejnol
- Sars International Centre for Marine Molecular Biology, University of Bergen, Thormøhlensgate 55, 5008 Bergen, Norway
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15
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Haszprunar G. Review of data for a morphological look on Xenacoelomorpha (Bilateria incertae sedis). ORG DIVERS EVOL 2015. [DOI: 10.1007/s13127-015-0249-z] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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16
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Raikova OI, Meyer-Wachsmuth I, Jondelius U. The plastic nervous system of Nemertodermatida. ORG DIVERS EVOL 2015. [DOI: 10.1007/s13127-015-0248-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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17
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18
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19
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New animal phylogeny: future challenges for animal phylogeny in the age of phylogenomics. ORG DIVERS EVOL 2015. [DOI: 10.1007/s13127-015-0236-4] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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20
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Kück P, Wägele JW. Plesiomorphic character states cause systematic errors in molecular phylogenetic analyses: a simulation study. Cladistics 2015; 32:461-478. [DOI: 10.1111/cla.12132] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/15/2015] [Indexed: 01/17/2023] Open
Affiliation(s)
- Patrick Kück
- The Natural History Museum Cromwell Road SW7 5BD London UK
| | - J. Wolfgang Wägele
- Zoologisches Forschungsmuseum Alexander Koenig Adenauerallee 160 53113 Bonn Germany
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21
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De Baets K, Dentzien-Dias P, Upeniece I, Verneau O, Donoghue PCJ. Constraining the Deep Origin of Parasitic Flatworms and Host-Interactions with Fossil Evidence. ADVANCES IN PARASITOLOGY 2015; 90:93-135. [PMID: 26597066 DOI: 10.1016/bs.apar.2015.06.002] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Novel fossil discoveries have contributed to our understanding of the evolutionary appearance of parasitism in flatworms. Furthermore, genetic analyses with greater coverage have shifted our views on the coevolution of parasitic flatworms and their hosts. The putative record of parasitic flatworms is consistent with extant host associations and so can be used to put constraints on the evolutionary origin of the parasites themselves. The future lies in new molecular clock analyses combined with additional discoveries of exceptionally preserved flatworms associated with hosts and coprolites. Besides direct evidence, the host fossil record and biogeography have the potential to constrain their evolutionary history, albeit with caution needed to avoid circularity, and a need for calibrations to be implemented in the most conservative way. This might result in imprecise, but accurate divergence estimates for the evolution of parasitic flatworms.
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Affiliation(s)
- Kenneth De Baets
- Fachgruppe PaläoUmwelt, GeoZentrum Nordbayern, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
| | - Paula Dentzien-Dias
- Núcleo de Oceanografia Geológica, Instituto de Oceanografia, Universidade Federal do Rio Grande, Rio Grande, Brazil
| | - Ieva Upeniece
- Department of Geology, University of Latvia, Riga, Latvia
| | - Olivier Verneau
- Centre de Formation et de Recherche sur les Environnements Méditerranéens, University of Perpignan Via Domitia, Perpignan, France; CNRS, Centre de Formation et de Recherche sur les Environnements Méditerranéens, Perpignan, France; Unit for Environmental Sciences and Management, North-West University, Potchefstroom, South Africa
| | - Philip C J Donoghue
- School of Earth Sciences, University of Bristol, Life Science Building, Bristol, UK
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22
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Dunn CW, Giribet G, Edgecombe GD, Hejnol A. Animal Phylogeny and Its Evolutionary Implications. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2014. [DOI: 10.1146/annurev-ecolsys-120213-091627] [Citation(s) in RCA: 261] [Impact Index Per Article: 26.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Casey W. Dunn
- Department of Ecology and Evolutionary Biology, Brown University, Providence, Rhode Island 02912;
| | - Gonzalo Giribet
- Museum of Comparative Zoology, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138;
| | - Gregory D. Edgecombe
- Department of Earth Sciences, The Natural History Museum, London SW7 5BD, United Kingdom;
| | - Andreas Hejnol
- Sars International Centre for Marine Molecular Biology, University of Bergen, 5008 Bergen, Norway;
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23
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Meyer-Wachsmuth I, Curini Galletti M, Jondelius U. Hyper-cryptic marine meiofauna: species complexes in Nemertodermatida. PLoS One 2014; 9:e107688. [PMID: 25225981 PMCID: PMC4166464 DOI: 10.1371/journal.pone.0107688] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2014] [Accepted: 08/08/2014] [Indexed: 01/30/2023] Open
Abstract
Nemertodermatida are microscopically small, benthic marine worms. Specimens of two nominal species, Sterreria psammicola and Nemertinoides elongatus from 33 locations worldwide were sequenced for three molecular markers. Species delimitation and validation was done using gene trees, haplotype networks and multilocus Bayesian analysis. We found 20 supported species of which nine: Nemertinoides glandulosum n.sp., N. wolfgangi n.sp., Sterreria boucheti n.sp., S. lundini n.sp., S. martindalei n.sp., S. monolithes n.sp., S. papuensis n.sp., S. variabilis n.sp. and S. ylvae n.sp., are described including nucleotide-based diagnoses. The distribution patterns indicate transoceanic dispersal in some of the species. Sympatric species were found in many cases. The high level of cryptic diversity in this meiofauna group implies that marine diversity may be higher than previously estimated.
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Affiliation(s)
- Inga Meyer-Wachsmuth
- Department of Zoology, Swedish Museum of Natural History, Stockholm, Sweden
- Department of Zoology, Stockholm University, Stockholm, Sweden
| | - Marco Curini Galletti
- Dipartimento di Scienze della Natura e del Territorio, Università di Sassari, Sassari, Italy
| | - Ulf Jondelius
- Department of Zoology, Swedish Museum of Natural History, Stockholm, Sweden
- Department of Zoology, Stockholm University, Stockholm, Sweden
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24
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The molecular symplesiomorphies shared by the stem groups of metazoan evolution: can sites as few as 1% have a significant impact on recognizing the phylogenetic position of myzostomida? J Mol Evol 2014; 79:63-74. [PMID: 25128981 DOI: 10.1007/s00239-014-9635-y] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2013] [Accepted: 07/22/2014] [Indexed: 10/24/2022]
Abstract
Although it is clear that taxon sampling, alignments, gene sampling, tree reconstruction methods and the total length of the sequences used are critical to the reconstruction of evolutionary history, weakly supported or misleading nodes exist in phylogenetic studies with no obvious flaw in those aspects. The phylogenetic studies focusing on the basal part of bilaterian evolution are such a case. During the past decade, Myzostomida has appeared in the basal part of Bilateria in several phylogenetic studies of Metazoa. However, most researchers have entertained only two competing hypotheses about the position of Myzostomida-an affinity with Annelida and an affinity with Platyhelminthes. In this study, dozens of symplesiomorphies were discovered by means of ancestral state reconstruction in the complete 18S and 28S rDNAs shared by the stem groups of Metazoa. By contrastive analysis on the datasets with or without such symplesiomorphic sites, we discovered that Myzostomida and other basal groups are basal lineages of Bilateria due to the corresponding symplesiomorphies shared with earlier lineages. As such, symplesiomorphies account for approximately 1-2% of the whole dataset have an essential impact on phylogenetic inference, and this study reminds molecular systematists of the importance of carrying out ancestral state reconstruction at each site in sequence-based phylogenetic studies. In addition, reasons should be explored for the low support of the hypothesis that Myzostomida belongs to Annelida in the results of phylogenomic studies. Future phylogenetic studies concerning Myzostomida should include all of the basal lineages of Bilateria to avoid directly neglecting the stand-alone basal position of Myzostomida as a potential hypothesis.
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25
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Protonephridia in the larvae of the paleonemertean species Carinoma mutabilis (Carinomidae, Nemertea) and Cephalothrix (Procephalothrix) filiformis (Cephalothricidae, Nemertea). ZOOMORPHOLOGY 2013. [DOI: 10.1007/s00435-013-0206-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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26
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The muscular system of Nemertoderma westbladi and Meara stichopi (Nemertodermatida, Acoelomorpha). ZOOMORPHOLOGY 2013. [DOI: 10.1007/s00435-013-0191-6] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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27
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Sakai M, Sakaizumi M. The complete mitochondrial genome of Dugesia japonica (Platyhelminthes; order Tricladida). Zoolog Sci 2012; 29:672-80. [PMID: 23030340 DOI: 10.2108/zsj.29.672] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
We used two sequencing methods, namely long polymerase chain reaction (PCR) and primer walking, to determine the complete mitochondrial DNA (mtDNA) sequence of Dugesia japonica and most of the mtDNA sequence of Dugesia ryukyuensis. The genome of D. japonica contained 36 genes including 12 of the 13 protein-coding genes characteristic of metazoan mitochondrial genomes, two ribosomal RNA genes, and 22 transfer RNA genes. The genome of D. ryukyuensis contained 33 genes, including 12 protein-coding genes, two ribosomal RNA genes, and 19 transfer RNA genes. The gene order of the mitochondrial genome from the Dugesia species showed no clear homology with either the Neodermata or other free-living Rhabditophora. This indicates that the platyhelminths exhibit great variability in mitochondrial gene order. This is the first complete sequence analysis of the mitochondrial genome of a free-living member of Rhabditophora, which will facilitate further studies on the population genetics and genomic evolution of the Platyhelminthes.
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Affiliation(s)
- Masato Sakai
- Graduate School of Science and Technology, Niigata University, 8050, Ikarashi 2-no-cho, Niigata 950-2181, Japan.
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Achatz JG, Chiodin M, Salvenmoser W, Tyler S, Martinez P. The Acoela: on their kind and kinships, especially with nemertodermatids and xenoturbellids (Bilateria incertae sedis). ORG DIVERS EVOL 2012; 13:267-286. [PMID: 24098090 PMCID: PMC3789126 DOI: 10.1007/s13127-012-0112-4] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Acoels are among the simplest worms and therefore have often been pivotal in discussions of the origin of the Bilateria. Initially thought primitive because of their “planula-like” morphology, including their lumenless digestive system, they were subsequently dismissed by many morphologists as a specialized clade of the Platyhelminthes. However, since molecular phylogenies placed them outside the Platyhelminthes and outside all other phyla at the base of the Bilateria, they became the focus of renewed debate and research. We review what is currently known of acoels, including information regarding their morphology, development, systematics, and phylogenetic relationships, and put some of these topics in a historical perspective to show how the application of new methods contributed to the progress in understanding these animals. Taking all available data into consideration, clear-cut conclusions cannot be made; however, in our view it becomes successively clearer that acoelomorphs are a “basal” but “divergent” branch of the Bilateria.
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Affiliation(s)
- Johannes G. Achatz
- Department of Genetics, University of Barcelona, Av. Diagonal, edifici annex, planta 2a, 08028 Barcelona, Spain
- Department of Evolutionary Developmental Biology, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
| | - Marta Chiodin
- Department of Genetics, University of Barcelona, Av. Diagonal, edifici annex, planta 2a, 08028 Barcelona, Spain
| | - Willi Salvenmoser
- Department of Evolutionary Developmental Biology, University of Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria
| | - Seth Tyler
- School of Biology and Ecology, University of Maine, 5751 Murray Hall, Orono, ME 04469 USA
| | - Pedro Martinez
- Department of Genetics, University of Barcelona, Av. Diagonal, edifici annex, planta 2a, 08028 Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys, 23, 08010 Barcelona, Spain
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Woodcock MR. Nested Hierarchal Organization of Conservation for MicroRNAs and Their Putative Targets to Drosophila melanogaster. Chem Biodivers 2012; 9:945-64. [DOI: 10.1002/cbdv.201100358] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Curini-Galletti M, Artois T, Delogu V, De Smet WH, Fontaneto D, Jondelius U, Leasi F, Martínez A, Meyer-Wachsmuth I, Nilsson KS, Tongiorgi P, Worsaae K, Todaro MA. Patterns of diversity in soft-bodied meiofauna: dispersal ability and body size matter. PLoS One 2012; 7:e33801. [PMID: 22457790 PMCID: PMC3311549 DOI: 10.1371/journal.pone.0033801] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2011] [Accepted: 02/17/2012] [Indexed: 11/30/2022] Open
Abstract
Background Biogeographical and macroecological principles are derived from patterns of distribution in large organisms, whereas microscopic ones have often been considered uninteresting, because of their supposed wide distribution. Here, after reporting the results of an intensive faunistic survey of marine microscopic animals (meiofauna) in Northern Sardinia, we test for the effect of body size, dispersal ability, and habitat features on the patterns of distribution of several groups. Methodology/Principal Findings As a dataset we use the results of a workshop held at La Maddalena (Sardinia, Italy) in September 2010, aimed at studying selected taxa of soft-bodied meiofauna (Acoela, Annelida, Gastrotricha, Nemertodermatida, Platyhelminthes and Rotifera), in conjunction with data on the same taxa obtained during a previous workshop hosted at Tjärnö (Western Sweden) in September 2007. Using linear mixed effects models and model averaging while accounting for sampling bias and potential pseudoreplication, we found evidence that: (1) meiofaunal groups with more restricted distribution are the ones with low dispersal potential; (2) meiofaunal groups with higher probability of finding new species for science are the ones with low dispersal potential; (3) the proportion of the global species pool of each meiofaunal group present in each area at the regional scale is negatively related to body size, and positively related to their occurrence in the endobenthic habitat. Conclusion/Significance Our macroecological analysis of meiofauna, in the framework of the ubiquity hypothesis for microscopic organisms, indicates that not only body size but mostly dispersal ability and also occurrence in the endobenthic habitat are important correlates of diversity for these understudied animals, with different importance at different spatial scales. Furthermore, since the Western Mediterranean is one of the best-studied areas in the world, the large number of undescribed species (37%) highlights that the census of marine meiofauna is still very far from being complete.
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Affiliation(s)
- Marco Curini-Galletti
- Dipartimento di Zoologia e Genetica Evoluzionistica, Università di Sassari, Sassari, Italy
| | - Tom Artois
- Centre for Environmental Sciences, Hasselt University, Diepenbeek, Belgium
| | - Valentina Delogu
- Dipartimento di Zoologia e Genetica Evoluzionistica, Università di Sassari, Sassari, Italy
| | | | - Diego Fontaneto
- Department of Invertebrate Zoology, Swedish Museum of Natural History, Stockholm, Sweden
- Division of Biology, Imperial College London, Ascot, United Kingdom
| | - Ulf Jondelius
- Department of Invertebrate Zoology, Swedish Museum of Natural History, Stockholm, Sweden
| | - Francesca Leasi
- Division of Biology, Imperial College London, Ascot, United Kingdom
- Dipartimento di Biologia, Universtità di Modena e Reggio Emilia, Modena, Italy
| | | | - Inga Meyer-Wachsmuth
- Department of Invertebrate Zoology, Swedish Museum of Natural History, Stockholm, Sweden
| | - Karin Sara Nilsson
- Department of Invertebrate Zoology, Swedish Museum of Natural History, Stockholm, Sweden
| | - Paolo Tongiorgi
- Dipartimento di Biologia, Universtità di Modena e Reggio Emilia, Modena, Italy
| | - Katrine Worsaae
- Marine Biological Section, University of Copenhagen, Helsingør, Denmark
| | - M. Antonio Todaro
- Dipartimento di Biologia, Universtità di Modena e Reggio Emilia, Modena, Italy
- * E-mail:
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Edgecombe GD, Giribet G, Dunn CW, Hejnol A, Kristensen RM, Neves RC, Rouse GW, Worsaae K, Sørensen MV. Higher-level metazoan relationships: recent progress and remaining questions. ORG DIVERS EVOL 2011. [DOI: 10.1007/s13127-011-0044-4] [Citation(s) in RCA: 206] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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33
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Kotikova EA, Raikova OI. Architectonics of the central nervous system of Acoela, Platyhelminthes, and Rotifera. J EVOL BIOCHEM PHYS+ 2011. [DOI: 10.1134/s002209300801012x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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34
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Damborenea C, Brusa F, Almagro I, Noreña C. A phylogenetic analysis of Stenostomum and its neotropical congeners, with a description of a new species from the Peruvian Amazon Basin. INVERTEBR SYST 2011. [DOI: 10.1071/is10026] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
This study reports Peruvian freshwater species of Stenostomum (Catenulida) from the upper Yurúa River of the Amazon Basin. A total of 11 species were found. One of them, Stenostomum ashanika, sp. nov., is described. It can be distinguished by: a pre-pharyngeal constriction; a small cauda; a small, rounded, mobile and ventrally directed pharynx; and a tri-radiate mouth. The remaining 10 species are reviewed and illustrated; eight are first records for Peru. A preliminary phylogenetic analysis of neotropical stenostomid species based on morphological data is undertaken, including all Rhynchoscolex, Stenostomum and Myostenostomum species described for the area. The Rhynchoscolex species are basal and paraphyletic; the species of Myostenostomum are monophyletic, within the Stenostomum clade, supported by the presence of a muscular gizzard in the anterior region of the intestine. Ciliated pits and rhabdoids are synapomorphies of the Stenostomum + Myostenostomum clade. This is the first morphological study of the relationships between stenostomid species. The most relevant characters in the phylogenetic analysis are those related to cerebral brain lobes. The results also show that many of the morphological characteristics of the species under study are poorly known and should be studied in more depth.
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Boone M, Willems M, Claeys M, Artois T. Spermatogenesis and the structure of the testes in Isodiametra pulchra (Isodiametridae, Acoela). ACTA ZOOL-STOCKHOLM 2010. [DOI: 10.1111/j.1463-6395.2010.00481.x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Mwinyi A, Bailly X, Bourlat SJ, Jondelius U, Littlewood DTJ, Podsiadlowski L. The phylogenetic position of Acoela as revealed by the complete mitochondrial genome of Symsagittifera roscoffensis. BMC Evol Biol 2010; 10:309. [PMID: 20942955 PMCID: PMC2973942 DOI: 10.1186/1471-2148-10-309] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2010] [Accepted: 10/13/2010] [Indexed: 11/10/2022] Open
Abstract
Background Acoels are simply organized unsegmented worms, lacking hindgut and anus. Several publications over recent years challenge the long-held view that acoels are early offshoots of the flatworms. Instead a basal position as sister group to all other bilaterian animals was suggested, mainly based on molecular evidence. This led to the view that features of acoels might reflect those of the last common ancestor of Bilateria, and resulted in several evo-devo studies trying to interpret bilaterian evolution using acoels as a proxy model for the "Urbilateria". Results We describe the first complete mitochondrial genome sequence of a member of the Acoela, Symsagittifera roscoffensis. Gene content and circular organization of the mitochondrial genome does not significantly differ from other bilaterian animals. However, gene order shows no similarity to any other mitochondrial genome within the Metazoa. Phylogenetic analyses of concatenated alignments of amino acid sequences from protein coding genes support a position of Acoela and Nemertodermatida as the sister group to all other Bilateria. Our data provided no support for a sister group relationship between Xenoturbellida and Acoela or Acoelomorpha. The phylogenetic position of Xenoturbella bocki as sister group to or part of the deuterostomes was also unstable. Conclusions Our phylogenetic analysis supports the view that acoels and nemertodermatids are the earliest divergent extant lineage of Bilateria. As such they remain a valid source for seeking primitive characters present in the last common ancestor of Bilateria. Gene order of mitochondrial genomes seems to be very variable among Acoela and Nemertodermatida and the groundplan for the metazoan mitochondrial genome remains elusive. More data are needed to interpret mitochondrial genome evolution at the base of Bilateria.
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Affiliation(s)
- Adina Mwinyi
- Department of Evolutionary Biology and Ecology, University of Bonn, An der Immenburg 1, 53121 Bonn, Germany.
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37
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Semmler H, Wanninger A. Myogenesis in two polyclad platyhelminths with indirect development, Pseudoceros canadensis and Stylostomum sanjuania. Evol Dev 2010; 12:210-21. [PMID: 20433460 DOI: 10.1111/j.1525-142x.2010.00405.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Myogenesis of two representatives of Platyhelminthes, Stylostomum sanjuania and Pseudoceros canadensis, was followed from egg deposition until well-differentiated free-swimming larval stages, using F-actin staining and confocal laserscanning microscopy. Zonulae adhaerentes are the only structures to stain before 50% of development between egg deposition and hatching in S. sanjuania, and before 67% of development in P. canadenis. Subsequently, irregular fibers appear in the embryo, followed by a helicoid muscle close to the apical pole. Three longitudinal muscle pairs form, of which the dorsal pair remains more pronounced than the others. Gradually, new muscles form by branching or from double-stranded muscle zones adjacent to existing muscles. This results in an elaborate muscular bodywall that consists of a single helicoid muscle as well as multiple circular and longitudinal muscles. Diverse retractor muscles insert at the sphincter muscles around the stomodeum. The overall arrangement and formation mode of the larval musculature appears very similar in both species, although only P. canadensis has a primary circular muscle posterior to the helicoid muscle. Muscle formation in the apical region of the embryo precedes that at the abapical pole and the primary longitudinal muscles form slightly later than the primary circular muscles. Myogenesis and larval myoanatomy appears highly conserved among polyclad flatworms, but differs significantly from that of other trochozoan clades. Our data suggest that the larval muscular ground pattern of polyclad larvae comprises a bodywall consisting of a helicoid muscle, circular and longitudinal muscles, several retractor muscles, and sphincter muscles around the stomodeum.
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Affiliation(s)
- Henrike Semmler
- Department of Biology, University of Copenhagen, Copenhagen Ø, Denmark
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38
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Mallatt J, Craig CW, Yoder MJ. Nearly complete rRNA genes assembled from across the metazoan animals: Effects of more taxa, a structure-based alignment, and paired-sites evolutionary models on phylogeny reconstruction. Mol Phylogenet Evol 2010; 55:1-17. [DOI: 10.1016/j.ympev.2009.09.028] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2008] [Revised: 08/28/2009] [Accepted: 09/22/2009] [Indexed: 10/20/2022]
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39
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Giribet G. A new dimension in combining data? The use of morphology and phylogenomic data in metazoan systematics. ACTA ZOOL-STOCKHOLM 2010. [DOI: 10.1111/j.1463-6395.2009.00420.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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40
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Moreno E, Nadal M, Baguñà J, Martínez P. Tracking the origins of the bilaterian Hox patterning system: insights from the acoel flatworm Symsagittifera roscoffensis. Evol Dev 2009; 11:574-81. [PMID: 19754713 DOI: 10.1111/j.1525-142x.2009.00363.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Genes of the Hox cluster encode for transcriptional regulators that show collinear expression along the anteroposterior (AP) body axis in all bilateral animals. However, it is still unclear when in the evolutionary history of bilaterians the Hox system first conferred positional identity along the AP-axis. Recent molecular phylogenies have convincingly shown that the acoel flatworms, traditionally classified within the Platyhelminthes, are the sister group of the remaining Bilateria, branching out before the common ancestor of protostomes, and deuterostomes (the so-called PDA). This key phylogenetic position offers the opportunity to search for the presence and early role of Hox cluster genes to pattern the AP axis in acoels. Here, we report on the cloning, genomic arrangement, and expression domains of Hox genes in Symsagittifera roscoffensis. Three Hox genes were detected: one from each of the major groups of Hox genes, which are anterior, central, and posterior. In bacterial artificial chromosome cloning, sequencing, and chromosomal fluorescence in situ hybridization, Hox genes were not observed as being clustered in a unique genomic region. Nevertheless, despite its dispersion within the genome, Hox genes are expressed in nested domains along the AP axis in the juvenile worm. The basic set of Hox genes in acoels and their coarse nested spatial deployment might be the first indicators of the role of Hox genes in the evolution of bilateral symmetry and AP positional identity from a hypothetical radial ancestor.
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Affiliation(s)
- Eduardo Moreno
- Department de Genètica, Universitat de Barcelona, 08028 Barcelona, Spain
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41
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Hejnol A, Obst M, Stamatakis A, Ott M, Rouse GW, Edgecombe GD, Martinez P, Baguñà J, Bailly X, Jondelius U, Wiens M, Müller WEG, Seaver E, Wheeler WC, Martindale MQ, Giribet G, Dunn CW. Assessing the root of bilaterian animals with scalable phylogenomic methods. Proc Biol Sci 2009; 276:4261-70. [PMID: 19759036 DOI: 10.1098/rspb.2009.0896] [Citation(s) in RCA: 488] [Impact Index Per Article: 32.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
A clear picture of animal relationships is a prerequisite to understand how the morphological and ecological diversity of animals evolved over time. Among others, the placement of the acoelomorph flatworms, Acoela and Nemertodermatida, has fundamental implications for the origin and evolution of various animal organ systems. Their position, however, has been inconsistent in phylogenetic studies using one or several genes. Furthermore, Acoela has been among the least stable taxa in recent animal phylogenomic analyses, which simultaneously examine many genes from many species, while Nemertodermatida has not been sampled in any phylogenomic study. New sequence data are presented here from organisms targeted for their instability or lack of representation in prior analyses, and are analysed in combination with other publicly available data. We also designed new automated explicit methods for identifying and selecting common genes across different species, and developed highly optimized supercomputing tools to reconstruct relationships from gene sequences. The results of the work corroborate several recently established findings about animal relationships and provide new support for the placement of other groups. These new data and methods strongly uphold previous suggestions that Acoelomorpha is sister clade to all other bilaterian animals, find diminishing evidence for the placement of the enigmatic Xenoturbella within Deuterostomia, and place Cycliophora with Entoprocta and Ectoprocta. The work highlights the implications that these arrangements have for metazoan evolution and permits a clearer picture of ancestral morphologies and life histories in the deep past.
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Affiliation(s)
- Andreas Hejnol
- Kewalo Marine Laboratory, University of Hawaii, 41 Ahui Street, Honolulu, HI 96813, USA.
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Todt C. Structure and evolution of the pharynx simplex in acoel flatworms (Acoela). J Morphol 2009; 270:271-90. [PMID: 18942704 DOI: 10.1002/jmor.10682] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The homology of pharynges within the mostly pharynx-less Acoela has been a matter of discussion for decades and even the basic question of whether a pharynx is a primitive trait within the Acoela and homologous to the pharynx of platyhelminth turbellarians is open. By using fluorescence staining of musculature, as well as conventional histological techniques and transmission electron microscopy, the present study sets focus on the mouth and pharynx (where present) of seven species of Acoela within Paratomellidae, Solenofilomorphidae, Hofsteniidae, Proporidae, and Convolutidae, as well as one species of Nemertodermatida and Catenulida, respectively. It is shown that among the investigated families of acoels there is a great variability in muscle systems associated with the mouth and pharynx and that pharynx histology and ultrastructural characters are widely diverse. There are no close similarities between the acoel pharynges and the catenulid pharynx but there is a general resemblance of the musculature associated with the mouth in the representatives of Paratomellidae and Nemertodermatida. On the basis of the profound differences in pharynx morphology, three major conclusions are drawn: 1) the pharynges as present in Recent acoels are not homologous to the pharynx simplex characteristic for Catenulida and Macrostomida within the Platyhelminthes; 2) the different muscular pharynx types of acoels are not homologous between higher taxa and thus a single acoel-type pharynx simplex cannot be defined; 3) the presence of a muscular pharynx most likely does not represent the ancestral state.
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Affiliation(s)
- Christiane Todt
- Department of Biology, University of Bergen, 5020 Bergen, Norway.
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Abstract
Since the discovery of the marine worm Xenoturbella bocki in 1915 by Sixten Bock and its first published description by Einar Westblad (Westblad,1949, Arkiv Zoologi 1:3-29), Xenoturbella was generally allied to the turbellarian flatworms, perhaps most closely to acoelomorphs. In 1997, however, analyses of ribosomal DNA (Norén and Jondelius, 1997, Nature 390:31-32) and developing oocytes (Israelsson, 1997, Nature 390:32) [and, subsequently, embryos (Israelsson, 1999, Proc R Soc Lond B 266:835-841)] recovered from Xenoturbella specimens led to the surprising conclusion that it was in fact a highly degenerate bivalve mollusc. Bourlat et al. showed in 2003 that this result was due to contamination from bivalves in its diet (Bourlat et al.,2003, Nature 424:925-928). Our analyses showed Xenoturbella is a deuterostome, related to the Ambulacraria (echinoderms and hemichordates). Subsequent work has shown that Xenoturbellida is a separate lineage from the Ambulacraria and therefore constitutes the fourth deuterostome phylum (Bourlat et al.,2006, Nature 444:85-88). I consider this phylogenetic position in the light of what is known of its genetics, morphology, and ontogeny. I examine what this phylogenetic position for Xenoturbella can tell us about its own evolution and what light this might shine on the common ancestor of the deuterostomes and hence on the origins of the chordates.
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Affiliation(s)
- Maximilian J Telford
- Department of Genetics, Evolution and Environment, University College London, London WC1E 6BT, UK.
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Fritzsch G, Böhme MU, Thorndyke M, Nakano H, Israelsson O, Stach T, Schlegel M, Hankeln T, Stadler PF. PCR survey of Xenoturbella bocki Hox genes. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2008; 310:278-84. [PMID: 18161857 DOI: 10.1002/jez.b.21208] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Xenoturbella bocki has recently been identified as one of the most basal deuterostomes, although an even more basal phylogenetic position cannot be ruled out. Here we report on a polymerase chain reaction survey of partial Hox homeobox sequences of X. bocki. Surprisingly, we did not find evidence for more than five Hox genes, one clear labial/PG1 ortholog, one posterior gene most similar to the PG9/10 genes of Ambulacraria, and three central group genes whose precise assignment to a specific paralog group remains open. We furthermore report on a re-evaluation of the available published evidence of Hox genes in other basal deuterostomes.
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Affiliation(s)
- Guido Fritzsch
- Interdisciplinary Center for Bioinformatics, University of Leipzig, Härtelstrasse Leipzig, Germany
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45
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Abstract
The advent of numerical methods for analysing phylogenetic relationships, along with the study of morphology and molecular data, has driven our understanding of animal relationships for the past three decades. Within the protostome branch of the animal tree of life, these data have sufficed to establish its two main side branches, the moulting Ecdysozoa and the non-moulting Lophotrochozoa. In this review, I explore our current knowledge of protostome relationships and discuss progress and future perspectives and strategies to increase resolution within the main lophotrochozoan clades. Novel approaches to coding morphological characters are needed by scoring real observations on species selected as terminals. Still, methodological issues, for example, how to deal with inapplicable characters or the coding of absences, may require novel algorithmic developments. Taxon sampling is another key issue, as phyla should include enough species so as to represent their span of anatomical disparity. On the molecular side, phylogenomics is playing an increasingly important role in elucidating animal relationships, but genomic sampling is still fairly limited within the lophotrochozoan protostomes, for which only three phyla are represented in currently available phylogenies. Future work should therefore concentrate on generating novel morphological observations and on producing genomic data for the lophotrochozoan side of the animal tree of life.
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Affiliation(s)
- Gonzalo Giribet
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
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Hejnol A, Martindale MQ. Acoel development supports a simple planula-like urbilaterian. Philos Trans R Soc Lond B Biol Sci 2008; 363:1493-501. [PMID: 18192185 PMCID: PMC2614228 DOI: 10.1098/rstb.2007.2239] [Citation(s) in RCA: 130] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Molecular approaches to the study of development and evolution have had profound effects on our understanding of the nature of the evolutionary process. Developmental biologists became intoxicated with fanciful notions of reconstructing genetic pathways of morphogenesis while evolutionary biologists were sobered by the fallacy of reconstructing organismal relationships along increasing grades of morphological complexity. Increased taxon sampling and improvements in analytical techniques are providing a new approach and are forcing biologists to move past historical biases to allow more accurate mapping of morphological and developmental characters through evolutionary time. Here, we discuss the possible developmental and morphological features of the 'urbilaterian', the triploblastic animal with anterior-posterior and dorsoventral axes and predecessor of the protostome-deuterostome ancestor. We argue that this animal, with features resembling acoelomorph flatworms, was far simpler morphologically than the protostome-deuterostome ancestor despite possessing a nearly complete eubilaterian genome. We show that the deployment of some genes expected to pattern the protostome-deuterostome ancestor is not deployed in acoels in the predicted manner and thus might have been co-opted after the evolution of the urbilaterian. We also identify the developmental changes related to gastrulation that gave rise to the urbilaterian from a simpler cnidarian-like ancestor.
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Affiliation(s)
| | - Mark Q Martindale
- Kewalo Marine Laboratory, Pacific Bioscience Research Center, University of Hawaii41 Ahui Street, Honolulu, HI 96813, USA
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Baguñà J, Martinez P, Paps J, Riutort M. Back in time: a new systematic proposal for the Bilateria. Philos Trans R Soc Lond B Biol Sci 2008; 363:1481-91. [PMID: 18192186 PMCID: PMC2615819 DOI: 10.1098/rstb.2007.2238] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Conventional wisdom suggests that bilateral organisms arose from ancestors that were radially, rather than bilaterally, symmetrical and, therefore, had a single body axis and no mesoderm. The two main hypotheses on how this transformation took place consider either a simple organism akin to the planula larva of extant cnidarians or the acoel Platyhelminthes (planuloid-acoeloid theory), or a rather complex organism bearing several or most features of advanced coelomate bilaterians (archicoelomate theory). We report phylogenetic analyses of bilaterian metazoans using quantitative (ribosomal, nuclear and expressed sequence tag sequences) and qualitative (HOX cluster genes and microRNA sets) markers. The phylogenetic trees obtained corroborate the position of acoel and nemertodermatid flatworms as the earliest branching extant members of the Bilateria. Moreover, some acoelomate and pseudocoelomate clades appear as early branching lophotrochozoans and deuterostomes. These results strengthen the view that stem bilaterians were small, acoelomate/pseudocoelomate, benthic organisms derived from planuloid-like organisms. Because morphological and recent gene expression data suggest that cnidarians are actually bilateral, the origin of the last common bilaterian ancestor has to be put back in time earlier than the cnidarian-bilaterian split in the form of a planuloid animal. A new systematic scheme for the Bilateria that includes the Cnidaria is suggested and its main implications discussed.
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Affiliation(s)
- Jaume Baguñà
- Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain.
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48
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Abstract
A review of the old and new literature on animal morphology/embryology and molecular studies has led me to the following scenario for the early evolution of the metazoans. The metazoan ancestor, "choanoblastaea," was a pelagic sphere consisting of choanocytes. The evolution of multicellularity enabled division of labor between cells, and an "advanced choanoblastaea" consisted of choanocytes and nonfeeding cells. Polarity became established, and an adult, sessile stage developed. Choanocytes of the upper side became arranged in a groove with the cilia pumping water along the groove. Cells overarched the groove so that a choanocyte chamber was formed, establishing the body plan of an adult sponge; the pelagic larval stage was retained but became lecithotrophic. The sponges radiated into monophyletic Silicea, Calcarea, and Homoscleromorpha. Homoscleromorph larvae show cell layers resembling true, sealed epithelia. A homoscleromorph-like larva developed an archenteron, and the sealed epithelium made extracellular digestion possible in this isolated space. This larva became sexually mature, and the adult sponge-stage was abandoned in an extreme progenesis. This eumetazoan ancestor, "gastraea," corresponds to Haeckel's gastraea. Trichoplax represents this stage, but with the blastopore spread out so that the endoderm has become the underside of the creeping animal. Another lineage developed a nervous system; this "neurogastraea" is the ancestor of the Neuralia. Cnidarians have retained this organization, whereas the Triploblastica (Ctenophora+Bilateria), have developed the mesoderm. The bilaterians developed bilaterality in a primitive form in the Acoelomorpha and in an advanced form with tubular gut and long Hox cluster in the Eubilateria (Protostomia+Deuterostomia). It is indicated that the major evolutionary steps are the result of suites of existing genes becoming co-opted into new networks that specify new structures. The evolution of the eumetazoan ancestor from a progenetic homoscleromorph larva implies that we, as well as all the other eumetazoans, are derived sponge larvae.
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Affiliation(s)
- Claus Nielsen
- Zoological Museum (The Natural History Museum of Denmark, University of Copenhagen), Universitetsparken 15, DK-2100 Copenhagen, Denmark
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49
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Hox genes and the parasitic flatworms: New opportunities, challenges and lessons from the free-living. Parasitol Int 2008; 57:8-17. [DOI: 10.1016/j.parint.2007.09.007] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2007] [Revised: 09/18/2007] [Accepted: 09/24/2007] [Indexed: 11/20/2022]
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50
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Sempere LF, Martinez P, Cole C, Baguñà J, Peterson KJ. Phylogenetic distribution of microRNAs supports the basal position of acoel flatworms and the polyphyly of Platyhelminthes. Evol Dev 2007; 9:409-15. [PMID: 17845513 DOI: 10.1111/j.1525-142x.2007.00180.x] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Phylogenetic analyses based on gene sequences suggest that acoel flatworms are not members of the phylum Platyhelminthes, but instead are the most basal branch of triploblastic bilaterians. Nonetheless, this result has been called into question. An alternative test is to use qualitative molecular markers that should, in principle, exclude the possibility of convergent (homoplastic) evolution in unrelated groups. microRNAs (miRNAs), noncoding regulatory RNA molecules that are under intense stabilizing selection, are a newly discovered set of phylogenetic markers that can resolve such taxonomic disputes. The acoel Childia sp. has recently been shown to possess a subset of the conserved core of miRNAs found across deuterostomes and protostomes, whereas a polyclad flatworm-in addition to this core subset-possesses miRNAs restricted to just protostomes. Here, we examine another acoel, Symsagittifera roscoffensis, and three other platyhelminths. Our results show that the distribution of miRNAs in S. roscoffensis parallels that of Childia. In addition, two of 13 new miRNAs cloned from a triclad flatworm are also found in other lophotrochozoan protostomes, but not in ecdysozoans, deuterostomes, or in basal metazoans including acoels. The limited set of miRNAs found in acoels, intermediate between the even more reduced set in cnidarians and the larger and expanding set in the rest of bilaterians, is compelling evidence for the basal position of acoel flatworms and the polyphyly of Platyhelminthes.
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Affiliation(s)
- Lorenzo F Sempere
- Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755, USA
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