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Herranz M, Leander BS, Pardos F, Boyle MJ. Neuroanatomy of mud dragons: a comprehensive view of the nervous system in Echinoderes (Kinorhyncha) by confocal laser scanning microscopy. BMC Evol Biol 2019; 19:86. [PMID: 30961520 PMCID: PMC6454755 DOI: 10.1186/s12862-019-1405-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2018] [Accepted: 02/26/2019] [Indexed: 12/17/2022] Open
Abstract
Background The Scalidophora (Kinorhyncha, Loricifera and Priapulida) have an important phylogenetic position as early branching ecdysozoans, yet the architecture of their nervous organ systems is notably underinvestigated. Without such information, and in the absence of a stable phylogenetic context, we are inhibited from producing adequate hypotheses about the evolution and diversification of ecdysozoan nervous systems. Here, we utilize confocal laser scanning microscopy to characterize serotonergic, tubulinergic and FMRFamidergic immunoreactivity patterns in a comparative neuroanatomical study with three species of Echinoderes, the most speciose, abundant and diverse genus within Kinorhyncha. Results Neuroanatomy in Echinoderes as revealed by acetylated α-tubulin immunoreactivity includes a circumpharyngeal brain and ten neurite bundles in the head region that converge into five longitudinal nerves within the trunk. The ventral nerve cord is ganglionated, emerging from the brain with two connectives that converge in trunk segments 2–3, and diverge again within segment 8. The longitudinal nerves and ventral nerve cord are connected by two transverse neurites in segments 2–9. Differences among species correlate with the number, position and innervation of cuticular structures along the body. Patterns of serotoninergic and FMRFamidergic immunoreactivity correlate with the position of the brain neuropil and the ventral nerve cord. Distinct serotonergic and FMRFamidergic somata are associated with the brain neuropil and specific trunk segments along the ventral nerve cord. Conclusions Neural architecture is highly conserved across all three species, suggesting that our results reveal a pattern that is common to more than 40% of the species within Kinorhyncha. The nervous system of Echinoderes is segmented along most of the trunk; however, posterior trunk segments exhibit modifications that are likely associated with sensorial, motor or reproductive functions. Although all kinorhynchs show some evidence of an externally segmented trunk, it is unclear whether external segmentation matches internal segmentation of nervous and muscular organ systems across Kinorhyncha, as we observed in Echinoderes. The neuroanatomical data provided in this study not only expand the limited knowledge on kinorhynch nervous systems but also establish a comparative morphological framework within Scalidophora that will support broader inferences about the evolution of neural architecture among the deepest branching lineages of the Ecdysozoa. Electronic supplementary material The online version of this article (10.1186/s12862-019-1405-4) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- María Herranz
- Departments of Zoology and Botany, University of British Columbia. Biodiversity Research Centre, 2212 Main Mall, Vancouver, BC, V6T 1Z4, Canada.
| | - Brian S Leander
- Departments of Zoology and Botany, University of British Columbia. Biodiversity Research Centre, 2212 Main Mall, Vancouver, BC, V6T 1Z4, Canada
| | - Fernando Pardos
- Departamento de Biodiversidad, Ecología y Evolución, Universidad Complutense de Madrid, C/José Antonio Novais, 22040, Madrid, Spain
| | - Michael J Boyle
- Smithsonian Institution, Smithsonian Marine Station at Fort Pierce, 701 Seaway Drive, Fort Pierce, Florida, 34949, USA
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Gross V, Treffkorn S, Reichelt J, Epple L, Lüter C, Mayer G. Miniaturization of tardigrades (water bears): Morphological and genomic perspectives. ARTHROPOD STRUCTURE & DEVELOPMENT 2019; 48:12-19. [PMID: 30447338 DOI: 10.1016/j.asd.2018.11.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2018] [Revised: 11/08/2018] [Accepted: 11/13/2018] [Indexed: 05/03/2023]
Abstract
Tardigrades form a monophyletic group of microscopic ecdysozoans best known for surviving extreme environmental conditions. Due to their key phylogenetic position as a subgroup of the Panarthropoda, understanding tardigrade biology is important for comparative studies with related groups like Arthropoda. Panarthropods - and Ecdysozoa as a whole - likely evolved from macroscopic ancestors, with several taxa becoming secondarily miniaturized. Morphological and genomic evidence likewise points to a miniaturized tardigrade ancestor. The five-segmented tardigrade body typically measures less than 1 mm in length and consists of only about 1000 cells. Most organs comprise a relatively small number of cells, with the highest proportion belonging to the central nervous system, while muscles are reduced to a single cell each. Similarly, fully sequenced genomes of three tardigrade species - together with Hox gene expression data - point to extensive modifications, rearrangements, and major losses of genes and even a large body region. Parallels are evident with related ecdysozoans that may have also undergone genomic reductions, such as the nematode Caenorhabditis elegans. We interpret these data together as evidence of miniaturization in the tardigrade lineage, while cautioning that the effects of miniaturization may manifest in different ways depending on the organ or organ system under examination.
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Affiliation(s)
- Vladimir Gross
- Department of Zoology, Institute of Biology, University of Kassel, Heinrich-Plett-Straße 40, Kassel, D-34132, Germany
| | - Sandra Treffkorn
- Department of Zoology, Institute of Biology, University of Kassel, Heinrich-Plett-Straße 40, Kassel, D-34132, Germany
| | - Julian Reichelt
- Department of Zoology, Institute of Biology, University of Kassel, Heinrich-Plett-Straße 40, Kassel, D-34132, Germany
| | - Lisa Epple
- Department of Zoology, Institute of Biology, University of Kassel, Heinrich-Plett-Straße 40, Kassel, D-34132, Germany
| | - Carsten Lüter
- Museum für Naturkunde, Leibniz-Institute for Evolution and Biodiversity Science, Invalidenstraße 43, Berlin, D-10115, Germany
| | - Georg Mayer
- Department of Zoology, Institute of Biology, University of Kassel, Heinrich-Plett-Straße 40, Kassel, D-34132, Germany.
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Bartels PJ, Apodaca J, Mora C, Nelson DR. A global biodiversity estimate of a poorly known taxon: phylum Tardigrada. Zool J Linn Soc 2016. [DOI: 10.1111/zoj.12441] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- Paul J. Bartels
- Department of Biology; Warren Wilson College; Asheville NC 28815 USA
| | - J.J. Apodaca
- Department of Biology; Warren Wilson College; Asheville NC 28815 USA
| | - Camilo Mora
- Department of Geography; University of Hawaii; Honolulu HI 96822 USA
| | - Diane R. Nelson
- Department of Biological Sciences; East Tennessee State University; Johnson City TN 37614 USA
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4
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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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Borner J, Rehm P, Schill RO, Ebersberger I, Burmester T. A transcriptome approach to ecdysozoan phylogeny. Mol Phylogenet Evol 2014; 80:79-87. [PMID: 25124096 DOI: 10.1016/j.ympev.2014.08.001] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2014] [Revised: 07/15/2014] [Accepted: 08/01/2014] [Indexed: 11/20/2022]
Abstract
The monophyly of Ecdysozoa, which comprise molting phyla, has received strong support from several lines of evidence. However, the internal relationships of Ecdysozoa are still contended. We generated expressed sequence tags from a priapulid (penis worm), a kinorhynch (mud dragon), a tardigrade (water bear) and five chelicerate taxa by 454 transcriptome sequencing. A multigene alignment was assembled from 63 taxa, which comprised after matrix optimization 24,249 amino acid positions with high data density (2.6% gaps, 19.1% missing data). Phylogenetic analyses employing various models support the monophyly of Ecdysozoa. A clade combining Priapulida and Kinorhyncha (i.e. Scalidophora) was recovered as the earliest branch among Ecdysozoa. We conclude that Cycloneuralia, a taxon erected to combine Priapulida, Kinorhyncha and Nematoda (and others), are paraphyletic. Rather Arthropoda (including Onychophora) are allied with Nematoda and Tardigrada. Within Arthropoda, we found strong support for most clades, including monophyletic Mandibulata and Pancrustacea. The phylogeny within the Euchelicerata remained largely unresolved. There is conflicting evidence on the position of tardigrades: While Bayesian and maximum likelihood analyses of only slowly evolving genes recovered Tardigrada as a sister group to Arthropoda, analyses of the full data set, and of subsets containing genes evolving at fast and intermediate rates identified a clade of Tardigrada and Nematoda. Notably, the latter topology is also supported by the analyses of indel patterns.
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Affiliation(s)
- Janus Borner
- Institute of Zoology and Zoological Museum, University of Hamburg, D-20146 Hamburg, Germany
| | - Peter Rehm
- Institute of Zoology and Zoological Museum, University of Hamburg, D-20146 Hamburg, Germany
| | - Ralph O Schill
- Zoology, Biological Institute, University of Stuttgart, Germany
| | - Ingo Ebersberger
- Department for Applied Bioinformatics, University of Frankfurt, Institute for Cell Biology and Neuroscience, Germany
| | - Thorsten Burmester
- Institute of Zoology and Zoological Museum, University of Hamburg, D-20146 Hamburg, Germany.
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Liu Y, Xiao S, Shao T, Broce J, Zhang H. The oldest known priapulid-like scalidophoran animal and its implications for the early evolution of cycloneuralians and ecdysozoans. Evol Dev 2014; 16:155-65. [PMID: 24754444 DOI: 10.1111/ede.12076] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Morphological phylogenetic analyses suggest that scalidophorans (priapulids, loriciferans, and kinorhynchs) and nematoids (nematodes and nematomorphs) form the ecdysozoan clade Cycloneuralia, which is a sister group to panarthropods. It has been proposed that extant priapulids and Cambrian priapulid-like scalidophorans, because of their conserved evolution, have the potential to illuminate the ancestral morphology, ecology, and developmental biology of highly derived ecdysozoans such as nematods and arthropods. As such, Cambrian fossils, particularly Markuelia and possibly olivooids, can inform the early evolution of scalidophorans, cycloneuralians, and ecdysozoans. However, the scalidophoran Markuelia is known exclusively as embryo fossils, and the olivooids have been alternatively interpreted as cnidarians or cycloneuralians. Here, we describe a post-embryonic scalidophoran fossil Eopriapulites sphinx new genus and species, which represents the oldest known scalidophoran, from the early Cambrian Period (∼535 Ma) in South China. E. sphinx is similar to modern scalidophorans in having an introvert armed with hollow scalids, a collar with coronal scalids, and a pharynx with pharyngeal teeth, but its scalids and pharyngeal teeth are arranged in a hexaradial pattern. Phylogenetically resolved as a stem-group scalidophoran, E. sphinx shares a hexaradial pattern with the hexaradial arrangement of certain anatomical structures in kinorhynchs, loriciferans, nematoids, and Cambrian fossils such as Eolympia pediculata, which could also be a scalidophoran. Thus, the bodyplan of ancestral cycloneuralians may have had a component of hexaradial symmetry (i.e., some but not necessarily all anatomical parts are hexaradially arranged). If panarthropods are nested within paraphyletic cycloneuralians, as several molecular phylogenetic analyses suggest, the ancestral ecdysozoans may have been a legless worm possibly with a component of hexaradial symmetry.
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Affiliation(s)
- Yunhuan Liu
- College of Earth Science and Resources, Chang'an University, Xi'an, 710054, China; Department of Geosciences, Virginia Tech, Blacksburg, VA, 24061, USA
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Herranz M, Boyle MJ, Pardos F, Neves RC. Comparative myoanatomy of Echinoderes (Kinorhyncha): a comprehensive investigation by CLSM and 3D reconstruction. Front Zool 2014; 11:31. [PMID: 24708877 PMCID: PMC4021568 DOI: 10.1186/1742-9994-11-31] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2014] [Accepted: 03/28/2014] [Indexed: 11/10/2022] Open
Abstract
INTRODUCTION Kinorhyncha is a clade of marine invertebrate meiofauna. Their body plan includes a retractable introvert bearing rings of cuticular spines, and a limbless trunk with distinct segmentation of nervous, muscular and epidermal organ systems. As derived members within the basal branch of Ecdysozoa, kinorhynchs may provide an important example of convergence on the evolution of segmentation within one of three bilaterian superclades. We describe the myoanatomy of Echinoderes, the most specious kinorhynch genus, and build upon historical studies of kinorhynch ultrastructure and gross morphology. This is the first multi-species comparison of a complete organ system by confocal microscopy and three-dimensional reconstruction within Kinorhyncha. RESULTS Myoanatomy of adult Echinoderes is composed of the following: Head with two mouth cone circular muscles, nine pairs of oral style muscles, ten introvert retractors, one introvert circular muscle, and fourteen introvert circular muscle retractors; Neck with one circular muscle; Trunk showing distinct pairs of ventral and dorsal muscles within segments 1-10, dorsoventral muscles within segments 3-10, diagonal muscles within segments 1-8, longitudinal fibers spanning segments 1-9, three pairs of terminal spine muscles, and one pair of male penile spine muscles; Gut showing a pharynx with ten alternating rings of radial and circular muscle fibers enclosed in a complex sheath of protractors and retractors, an orthogonal grid of longitudinal and circular fibers surrounding the intestine, and paired hindgut dilators. CONCLUSIONS Myoanatomy is highly conserved between species of Echinoderes. Interspecific variation is observed in the arrangement and number of introvert fibers and the composition of pharyngeal muscles. Segmented trunk musculature facilitates the movements of articulated cuticular plates along the anterior-posterior axis. Intersegmental muscle fibers assist with dorsoventral and lateral trunk movements. Protractors, retractors and circular muscles coordinate eversion and retraction of the introvert and mouth cone, and relocation of the pharynx during locomotion and feeding behaviors. Pairs of posterior fibers suggest independent movements of terminal spines, and male penile spines. Within Scalidophora, myoanatomy is more similar between Kinorhyncha and Loricifera, than either group is to Priapulida. Kinorhynch myoanatomy may reflect a convergent transition from vermiform to segmented body plans during the early radiation of Ecdysozoa.
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Affiliation(s)
- María Herranz
- Dpto. Zoología y Antropología Física (Zoología de Invertebrados), Facultad de Biología, Universidad Complutense de Madrid, C/José Antonio Novais, 2, Madrid 28040, Spain
| | - Michael J Boyle
- Smithsonian Tropical Research Institute (STRI), Naos Marine Laboratories, Panama 0843/03092, Republic of Panama
| | - Fernando Pardos
- Dpto. Zoología y Antropología Física (Zoología de Invertebrados), Facultad de Biología, Universidad Complutense de Madrid, C/José Antonio Novais, 2, Madrid 28040, Spain
| | - Ricardo C Neves
- Biozentrum, University of Basel, Klingelbergstrasse 50, CH-4056 Basel, Switzerland
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8
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Persson DK, Halberg KA, Jørgensen A, Møbjerg N, Kristensen RM. Brain anatomy of the marine tardigradeactinarctus doryphorus(arthrotardigrada). J Morphol 2013; 275:173-90. [DOI: 10.1002/jmor.20207] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2013] [Revised: 07/01/2013] [Accepted: 08/19/2013] [Indexed: 11/08/2022]
Affiliation(s)
- Dennis K. Persson
- Department of Invertebrate Zoology, Natural History Museum of Denmark; University of Copenhagen, Universitetsparken 15; DK-2100 Copenhagen Ø Denmark
- Department of Biology, August Krogh Centre; University of Copenhagen, Universitetsparken 13; DK-2100 Copenhagen Ø Denmark
| | - Kenneth A. Halberg
- Department of Biology, August Krogh Centre; University of Copenhagen, Universitetsparken 13; DK-2100 Copenhagen Ø Denmark
| | - Aslak Jørgensen
- Laboratory of Molecular Systematics, Natural History Museum of Denmark; University of Copenhagen; Sølvgade 83 DK-1307 Copenhagen K Denmark
| | - Nadja Møbjerg
- Department of Biology, August Krogh Centre; University of Copenhagen, Universitetsparken 13; DK-2100 Copenhagen Ø Denmark
| | - Reinhardt M. Kristensen
- Department of Invertebrate Zoology, Natural History Museum of Denmark; University of Copenhagen, Universitetsparken 15; DK-2100 Copenhagen Ø Denmark
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9
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Herranz M, Pardos F, Boyle MJ. Comparative morphology of serotonergic-like immunoreactive elements in the central nervous system of kinorhynchs (Kinorhyncha, Cyclorhagida). J Morphol 2012; 274:258-74. [PMID: 23109054 DOI: 10.1002/jmor.20089] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2012] [Revised: 09/01/2012] [Accepted: 09/15/2012] [Indexed: 11/06/2022]
Abstract
Cycloneuralian taxa exhibit similar organ system architectures, providing informative characters of metazoan evolution, yet very few modern comparative descriptions of cellular and molecular homologies within and among those taxa are available. We immunolabeled and characterized elements of the serotonergic nervous system in the kinorhynchs Echinoderes spinifurca, Antygomonas paulae, and Zelinkaderes brightae using confocal laser scanning microscopy. Fluorescent markers targeting DNA were combined with observations of auto-fluorescent structures to guide interpretations of the internal and external anatomy in each species. Results show a common pattern of the central nervous system with a circumenteric brain divided into ring-shaped anterior and posterior neuronal somata and a central neuropil connected to a multi-stringed, longitudinal ventral nerve cord. Structural similarities and differences in the nervous systems of these species were observed and described, stressing the incomplete ring nature of the anterior region of the kinorhynch brain, the functional relationship between the brain and the movable introvert, and the number and arrangement of nerve strings and somata of the ventral nerve cord. The ventral cord ends in two ventrolateral cell bodies in E. spinifurca, and forms a terminal loop associated with a midterminal spine in A. paulae and Z. brightae. The possible functional and phylogenetic significance of these features and arrangements are discussed.
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Affiliation(s)
- María Herranz
- Departamento de Zoología y Antropología Física, Facultad de Biología, Universidad Complutense de Madrid, C/José Antonio Novais, 2, 28040 Madrid, Spain.
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Persson DK, Halberg KA, Jørgensen A, Møbjerg N, Kristensen RM. Neuroanatomy ofHalobiotus crispae(Eutardigrada: Hypsibiidae): Tardigrade brain structure supports the clade panarthropoda. J Morphol 2012; 273:1227-45. [DOI: 10.1002/jmor.20054] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2011] [Revised: 04/26/2012] [Accepted: 05/27/2012] [Indexed: 12/18/2022]
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Obinata T, Ono K, Ono S. Detection of a troponin I-like protein in non-striated muscle of the tardigrades (water bears). BIOARCHITECTURE 2011; 1:96-102. [PMID: 21866271 DOI: 10.4161/bioa.1.2.16251] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2011] [Accepted: 04/29/2011] [Indexed: 12/29/2022]
Abstract
Tardigrades, also known as water bears, have somatic muscle fibers that are responsible for movement of their body and legs. These muscle fibers contain thin and thick filaments in a non-striated pattern. However, the regulatory mechanism of muscle contraction in tardigrades is unknown. In the absence of extensive molecular and genomic information, we detected a protein of 31 kDa in whole lysates of tardigrades that cross-reacted with the antibody raised against nematode troponin I (TnI). TnI is a component of the troponin complex that regulates actin-myosin interaction in a Ca(2+)-dependent and actin-linked manner. This TnI-like protein was co-extracted with actin in a buffer containing ATP and EGTA, which is known to induce relaxation of a troponin-regulated contractile system. The TnI-like protein was specifically expressed in the somatic muscle fibers in adult animals and partially co-localized with actin filaments in a non-striated manner. Interestingly, the pharyngeal muscle did not express this protein. These observations suggest that the non-striated somatic muscle of tardigrades has an actin-linked and troponin-regulated system for muscle contraction.
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Affiliation(s)
- Takashi Obinata
- Department of Biology; Faculty of Science; Chiba University; Chiba, Japan
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D′Haese J, Traore‐Freitag A, Kiehl E, Prasath T, Greven H. The actin gene of
Hypsibius klebelsbergi
(Eutardigrada) – complete sequence and comparison with actin from related and non‐related taxa. J ZOOL SYST EVOL RES 2011. [DOI: 10.1111/j.1439-0469.2010.00604.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jochen D′Haese
- Institut für Zoomorphologie und Zellbiologie der Heinrich‐Heine‐Universität Düsseldorf, Düsseldorf, Germany
| | - Assita Traore‐Freitag
- Institut für Zoomorphologie und Zellbiologie der Heinrich‐Heine‐Universität Düsseldorf, Düsseldorf, Germany
| | - Ernst Kiehl
- Institut für Zoomorphologie und Zellbiologie der Heinrich‐Heine‐Universität Düsseldorf, Düsseldorf, Germany
| | - Thiruketheeswaran Prasath
- Institut für Zoomorphologie und Zellbiologie der Heinrich‐Heine‐Universität Düsseldorf, Düsseldorf, Germany
| | - Hartmut Greven
- Institut für Zoomorphologie und Zellbiologie der Heinrich‐Heine‐Universität Düsseldorf, Düsseldorf, Germany
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Rota-Stabelli O, Campbell L, Brinkmann H, Edgecombe GD, Longhorn SJ, Peterson KJ, Pisani D, Philippe H, Telford MJ. A congruent solution to arthropod phylogeny: phylogenomics, microRNAs and morphology support monophyletic Mandibulata. Proc Biol Sci 2010; 278:298-306. [PMID: 20702459 DOI: 10.1098/rspb.2010.0590] [Citation(s) in RCA: 200] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
While a unique origin of the euarthropods is well established, relationships between the four euarthropod classes-chelicerates, myriapods, crustaceans and hexapods-are less clear. Unsolved questions include the position of myriapods, the monophyletic origin of chelicerates, and the validity of the close relationship of euarthropods to tardigrades and onychophorans. Morphology predicts that myriapods, insects and crustaceans form a monophyletic group, the Mandibulata, which has been contradicted by many molecular studies that support an alternative Myriochelata hypothesis (Myriapoda plus Chelicerata). Because of the conflicting insights from published molecular datasets, evidence from nuclear-coding genes needs corroboration from independent data to define the relationships among major nodes in the euarthropod tree. Here, we address this issue by analysing two independent molecular datasets: a phylogenomic dataset of 198 protein-coding genes including new sequences for myriapods, and novel microRNA complements sampled from all major arthropod lineages. Our phylogenomic analyses strongly support Mandibulata, and show that Myriochelata is a tree-reconstruction artefact caused by saturation and long-branch attraction. The analysis of the microRNA dataset corroborates the Mandibulata, showing that the microRNAs miR-965 and miR-282 are present and expressed in all mandibulate species sampled, but not in the chelicerates. Mandibulata is further supported by the phylogenetic analysis of a comprehensive morphological dataset covering living and fossil arthropods, and including recently proposed, putative apomorphies of Myriochelata. Our phylogenomic analyses also provide strong support for the inclusion of pycnogonids in a monophyletic Chelicerata, a paraphyletic Cycloneuralia, and a common origin of Arthropoda (tardigrades, onychophorans and arthropods), suggesting that previous phylogenies grouping tardigrades and nematodes may also have been subject to tree-reconstruction artefacts.
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Affiliation(s)
- Omar Rota-Stabelli
- Department of Genetics, Evolution and Environment, University College London, , Darwin Building, Gower Street, London WC1E 6BT, UK
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Halberg KA, Persson D, Møbjerg N, Wanninger A, Kristensen RM. Myoanatomy of the marine tardigrade Halobiotus crispae (Eutardigrada: Hypsibiidae). J Morphol 2009; 270:996-1013. [PMID: 19274743 DOI: 10.1002/jmor.10734] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The muscular architecture of Halobiotus crispae (Eutardigrada: Hypsibiidae) was examined by means of fluorescent-coupled phalloidin in combination with confocal laser scanning microscopy and computer-aided three-dimensional reconstruction, in addition to light microscopy (Nomarski), scanning electron microscopy, and transmission electron microscopy (TEM). The somatic musculature of H. crispae is composed of structurally independent muscle fibers, which can be divided into a dorsal, ventral, dorsoventral, and a lateral musculature. Moreover, a distinct leg musculature is found. The number and arrangement of muscles differ in each leg. Noticeably, the fourth leg contains much fewer muscles when compared with the other legs. Buccopharyngeal musculature (myoepithelial muscles), intestinal musculature, and cloacal musculature comprise the animal's visceral musculature. TEM of stylet and leg musculature revealed ultrastructural similarities between these two muscle groups. Furthermore, microtubules are found in the epidermal cells of both leg and stylet muscle attachments. This would indicate that the stylet and stylet glands are homologues to the claw and claw glands, respectively. When comparing with previously published data on both heterotardigrade and eutardigrade species, it becomes obvious that eutardigrades possess very similar numbers and arrangement of muscles, yet differ in a number of significant details of their myoanatomy. This study establishes a morphological framework for the use of muscular architecture in elucidating tardigrade phylogeny.
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Affiliation(s)
- Kenneth Agerlin Halberg
- Department of Biology, The August Krogh Building, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark.
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Paps J, Baguñà J, Riutort M. Lophotrochozoa internal phylogeny: new insights from an up-to-date analysis of nuclear ribosomal genes. Proc Biol Sci 2009; 276:1245-54. [PMID: 19129141 PMCID: PMC2660960 DOI: 10.1098/rspb.2008.1574] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Resolving the relationships among animal phyla is a key biological problem that remains to be solved. Morphology is unable to determine the relationships among most phyla and although molecular data have unveiled a new evolutionary scenario, they have their own limitations. Nuclear ribosomal genes (18S and 28S rDNA) have been used effectively for many years. However, they are considered of limited use for resolving deep divergences such as the origin of the bilaterians, due to certain drawbacks such as the long-branch attraction (LBA) problem. Here, we attempt to overcome these pitfalls by combining several methods suggested in previous studies and routinely used in contemporary standard phylogenetic analyses but that have not yet been applied to any bilaterian phylogeny based on these genes. The methods used include maximum likelihood and Bayesian inference, the application of models with rate heterogeneity across sites, wide taxon sampling and compartmentalized analyses for each problematic clade. The results obtained show that the combination of the above-mentioned methodologies minimizes the LBA effect, and a new Lophotrochozoa phylogeny emerges. Also, the Acoela and Nemertodermatida are confirmed with maximum support as the first branching bilaterians. Ribosomal RNA genes are thus a reliable source for the study of deep divergences in the metazoan tree, provided that the data are treated carefully.
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Affiliation(s)
- Jordi Paps
- Departament de Genetica, Universitat de Barcelona, Avenida Diagonal, 645, 08028 Barcelona, Spain
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Greven H. Comments on the eyes of tardigrades. ARTHROPOD STRUCTURE & DEVELOPMENT 2007; 36:401-7. [PMID: 18089118 DOI: 10.1016/j.asd.2007.06.003] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2007] [Accepted: 06/25/2007] [Indexed: 05/19/2023]
Abstract
A survey is given on the scarce information on the visual organs (eyes or ocelli) of Tardigrada. Many Eutardigrada and some Arthrotardigrada, namely the Echiniscidae, possess inverse pigment-cup ocelli, which are located in the outer lobe of the brain, and probably are of cerebral origin. Occurrence of such organs in tardigrades, suggested as being eyeless, has never been checked. Depending on the species, response to light (photokinesis) is negative, positive or indifferent, and may change during the ontogeny. The tardigrade eyes of the two eutardigrades examined up to now comprise a single pigment cup cell, one or two microvillous (rhabdomeric) sensory cells and ciliary sensory cell(s). In the eyes of the eutardigrade Milnesium tardigradum the cilia are differentiated in an outer branching segment and an inner (dendritic) segment. Because of the scarcity of information on the tardigrade eyes, their homology with the visual organs of other bilaterians is currently difficult to establish and further comparative studies are needed. Thus, the significance of these eyes for the evolution of arthropod visual systems is unclear yet.
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Affiliation(s)
- Hartmut Greven
- Institut für Zoomorphologie und Zellbiologie der Heinrich-Heine-Universität Düsseldorf, Universitätsstr. 1, D-40225 Düsseldorf, Germany.
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Three-dimensional reconstruction of the central nervous system of Macrobiotus hufelandi (Eutardigrada, Parachela): implications for the phylogenetic position of Tardigrada. ZOOMORPHOLOGY 2007. [DOI: 10.1007/s00435-007-0045-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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18
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Hochberg R. Comparative immunohistochemistry of the cerebral ganglion in Gastrotricha: an analysis of FMRFamide-like immunoreactivity in Neodasys cirritus (Chaetonotida), Xenodasys riedli and Turbanella cf. hyalina (Macrodasyida). ZOOMORPHOLOGY 2007. [DOI: 10.1007/s00435-007-0044-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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19
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The tardigrade Hypsibius dujardini, a new model for studying the evolution of development. Dev Biol 2007; 312:545-59. [PMID: 17996863 DOI: 10.1016/j.ydbio.2007.09.055] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2007] [Revised: 09/12/2007] [Accepted: 09/28/2007] [Indexed: 01/01/2023]
Abstract
Studying development in diverse taxa can address a central issue in evolutionary biology: how morphological diversity arises through the evolution of developmental mechanisms. Two of the best-studied developmental model organisms, the arthropod Drosophila and the nematode Caenorhabditis elegans, have been found to belong to a single protostome superclade, the Ecdysozoa. This finding suggests that a closely related ecdysozoan phylum could serve as a valuable model for studying how developmental mechanisms evolve in ways that can produce diverse body plans. Tardigrades, also called water bears, make up a phylum of microscopic ecdysozoan animals. Tardigrades share many characteristics with C. elegans and Drosophila that could make them useful laboratory models, but long-term culturing of tardigrades historically has been a challenge, and there have been few studies of tardigrade development. Here, we show that the tardigrade Hypsibius dujardini can be cultured continuously for decades and can be cryopreserved. We report that H. dujardini has a compact genome, a little smaller than that of C. elegans or Drosophila, and that sequence evolution has occurred at a typical rate. H. dujardini has a short generation time, 13-14 days at room temperature. We have found that the embryos of H. dujardini have a stereotyped cleavage pattern with asymmetric cell divisions, nuclear migrations, and cell migrations occurring in reproducible patterns. We present a cell lineage of the early embryo and an embryonic staging series. We expect that these data can serve as a platform for using H. dujardini as a model for studying the evolution of developmental mechanisms.
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Gabriel WN, Goldstein B. Segmental expression of Pax3/7 and engrailed homologs in tardigrade development. Dev Genes Evol 2007; 217:421-33. [PMID: 17516081 DOI: 10.1007/s00427-007-0152-5] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2006] [Accepted: 03/28/2007] [Indexed: 10/23/2022]
Abstract
How morphological diversity arises through evolution of gene sequence is a major question in biology. In Drosophila, the genetic basis for body patterning and morphological segmentation has been studied intensively. It is clear that some of the genes in the Drosophila segmentation program are functioning similarly in certain other taxa, although many questions remain about when these gene functions arose and which taxa use these genes similarly to establish diverse body plans. Tardigrades are an outgroup to arthropods in the Ecdysozoa and, as such, can provide insight into how gene functions have evolved among the arthropods and their close relatives. We developed immunostaining methods for tardigrade embryos, and we used cross-reactive antibodies to investigate the expression of homologs of the pair-rule gene paired (Pax3/7) and the segment polarity gene engrailed in the tardigrade Hypsibius dujardini. We find that in H. dujardini embryos, Pax3/7 protein localizes not in a pair-rule pattern but in a segmentally iterated pattern, after the segments are established, in regions of the embryo where neurons later arise. Engrailed protein localizes in the posterior ectoderm of each segment before ectodermal segmentation is apparent. Together with previous results from others, our data support the conclusions that the pair-rule function of Pax3/7 is specific to the arthropods, that some of the ancient functions of Pax3/7 and Engrailed in ancestral bilaterians may have been in neurogenesis, and that Engrailed may have a function in establishing morphological boundaries between segments that is conserved at least among the Panarthropoda.
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Affiliation(s)
- Willow N Gabriel
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3280, USA
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Massey SE, Garey JR. A comparative genomics analysis of codon reassignments reveals a link with mitochondrial proteome size and a mechanism of genetic code change via suppressor tRNAs. J Mol Evol 2007; 64:399-410. [PMID: 17390094 DOI: 10.1007/s00239-005-0260-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2005] [Accepted: 12/12/2006] [Indexed: 10/23/2022]
Abstract
Using a comparative genomics approach we demonstrate a negative correlation between the number of codon reassignments undergone by 222 mitochondrial genomes and the mitochondrial genome size, the number of mitochondrial ORFs, and the sizes of the large and small subunit mitochondrial rRNAs. In addition, we show that the TGA-to-tryptophan codon reassignment, which has occurred 11 times in mitochondrial genomes, is found in mitochondrial genomes smaller than those which have not undergone the reassignment. We therefore propose that mitochondrial codon reassignments occur in a wide range of phyla, particularly in Metazoa, due to a reduced "proteomic constraint" on the mitochondrial genetic code, compared to the nuclear genetic code. The reduced proteomic constraint reflects the small size of the mitochondrial-encoded proteome and allows codon reassignments to occur with less likelihood of lethality. In addition, we demonstrate a striking link between nonsense codon reassignments and the decoding properties of naturally occurring nonsense suppressor tRNAs. This suggests that natural preexisting nonsense suppression facilitated nonsense codon reassignments and constitutes a novel mechanism of genetic code change. These findings explain for the first time the identity of the stop codons and amino acids reassigned in mitochondrial and nuclear genomes. Nonsense suppressor tRNAs provided the raw material for nonsense codon reassignments, implying that the properties of the tRNA anticodon have dictated the identity of nonsense codon reassignments.
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Affiliation(s)
- Steven E Massey
- Department of Biology, University of South Florida, 4202 East Fowler Avenue, Tampa, FL 33620, USA.
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Mallatt J, Giribet G. Further use of nearly complete 28S and 18S rRNA genes to classify Ecdysozoa: 37 more arthropods and a kinorhynch. Mol Phylogenet Evol 2006; 40:772-94. [PMID: 16781168 DOI: 10.1016/j.ympev.2006.04.021] [Citation(s) in RCA: 176] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2005] [Revised: 02/28/2006] [Accepted: 04/03/2006] [Indexed: 10/24/2022]
Abstract
This work expands on a study from 2004 by Mallatt, Garey, and Shultz [Mallatt, J.M., Garey, J.R., Shultz, J.W., 2004. Ecdysozoan phylogeny and Bayesian inference: first use of nearly complete 28S and 18S rRNA gene sequences to classify the arthropods and their kin. Mol. Phylogenet. Evol. 31, 178-191] that evaluated the phylogenetic relationships in Ecdysozoa (molting animals), especially arthropods. Here, the number of rRNA gene-sequences was effectively doubled for each major group of arthropods, and sequences from the phylum Kinorhyncha (mud dragons) were also included, bringing the number of ecdysozoan taxa to over 80. The methods emphasized maximum likelihood, Bayesian inference and statistical testing with parametric bootstrapping, but also included parsimony and minimum evolution. Prominent findings from our combined analysis of both genes are as follows. The fundamental subdivisions of Hexapoda (insects and relatives) are Insecta and Entognatha, with the latter consisting of collembolans (springtails) and a clade of proturans plus diplurans. Our rRNA-gene data provide the strongest evidence to date that the sister group of Hexapoda is Branchiopoda (fairy shrimps, tadpole shrimps, etc.), not Malacostraca. The large, Pancrustacea clade (hexapods within a paraphyletic Crustacea) divided into a few basic subclades: hexapods plus branchiopods; cirripedes (barnacles) plus malacostracans (lobsters, crabs, true shrimps, isopods, etc.); and the basally located clades of (a) ostracods (seed shrimps) and (b) branchiurans (fish lice) plus the bizarre pentastomids (tongue worms). These findings about Pancrustacea agree with a recent study by Regier, Shultz, and Kambic that used entirely different genes [Regier, J.C., Shultz, J.W., Kambic, R.E., 2005a. Pancrustacean phylogeny: hexapods are terrestrial crustaceans and maxillopods are not monophyletic. Proc. R. Soc. B 272, 395-401]. In Malacostraca, the stomatopod (mantis shrimp) was not at the base of the eumalacostracans, as is widely claimed, but grouped instead with an euphausiacean (krill). Within centipedes, Craterostigmus was the sister to all other pleurostigmophorans, contrary to the consensus view. Our trees also united myriapods (millipedes and centipedes) with chelicerates (horseshoe crabs, spiders, scorpions, and relatives) and united pycnogonids (sea spiders) with chelicerates, but with much less support than in the previous rRNA-gene study. Finally, kinorhynchs joined priapulans (penis worms) at the base of Ecdysozoa.
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Affiliation(s)
- Jon Mallatt
- School of Biological Sciences, Washington State University, Pullman, 99164-4236, USA.
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Todaro MA, Telford MJ, Lockyer AE, Littlewood DTJ. Interrelationships of the Gastrotricha and their place among the Metazoa inferred from 18S rRNA genes. ZOOL SCR 2006. [DOI: 10.1111/j.1463-6409.2006.00228.x] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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24
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Dong XP, Donoghue PCJ, Cunningham JA, Liu JB, Cheng H. The anatomy, affinity, and phylogenetic significance of Markuelia. Evol Dev 2005; 7:468-82. [PMID: 16174039 DOI: 10.1111/j.1525-142x.2005.05050.x] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The fossil record provides a paucity of data on the development of extinct organisms, particularly for their embryology. The recovery of fossilized embryos heralds new insight into the evolution of development but advances are limited by an almost complete absence of phylogenetic constraint. Markuelia is an exception to this, known from cleavage and pre-hatchling stages as a vermiform and profusely annulated direct-developing bilaterian with terminal circumoral and posterior radial arrays of spines. Phylogenetic analyses have hitherto suggested assignment to stem-Scalidophora (phyla Kinorhyncha, Loricifera, Priapulida). We test this assumption with additional data and through the inclusion of additional taxa. The available evidence supports stem-Scalidophora affinity, leading to the conclusion that scalidophorans, cyclonerualians, and ecdysozoans are primitive direct developers, and the likelihood that scalidophorans are primitively metameric.
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Affiliation(s)
- Xi-Ping Dong
- Department of Earth and Space Sciences, Peking University, Beijing 100871, China
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Hejnol A, Schnabel R. The eutardigrade Thulinia stephaniae has an indeterminate development and the potential to regulate early blastomere ablations. Development 2005; 132:1349-61. [PMID: 15716338 DOI: 10.1242/dev.01701] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
We present a detailed analysis of the cell lineage of the tardigrade Thulinia stephaniae with a 4D-microscopy system (3D time-lapse recording). The recording, of the entire development from embryogenesis until hatching, allowed us to analyze the fate of single descendants from early blastomeres up to germ layer formation and tissue development. The embryo undergoes an irregular indeterminate cleavage pattern without early fate restriction. During gastrulation, mesodermal and endodermal precursors, and a pair of primordial germ cells migrate through a blastopore at the prospective position of the mouth. Our results are not consistent with earlier descriptions of mesoderm formation by enterocoely in tardigrades. The mesoderm in Thulinia stephaniae originates from a variable number of blastomeres, which form mesodermal bands that later produce the serial somites. The nervous system is formed by neural progenitor cells, which delaminate from the neurogenic ectoderm. Early embryogenesis of Thulinia stephaniae is highly regulative, even after laser ablations of blastomeres at the two- and four-cell stages 'normal' juveniles are formed. This has never been observed before for a protostome. Germ cell specification occurs late during development between the sixth and seventh cell generation. Comparing the development of other protostomes with that of the Tardigrada, which occupy a basal position within the Arthropoda, suggests that an indeterminate cleavage and regulatory development is not only part of the ground pattern of the Arthropoda, but probably of the entire Ecdysozoa.
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Affiliation(s)
- Andreas Hejnol
- Technische Universität Braunschweig, Institut für Genetik, Spielmannstrasse 7, D-38106 Braunschweig, Germany
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Affiliation(s)
- Kenneth M. Halanych
- Department of Biological Sciences, Auburn University, Auburn, Alabama 36849;
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Mallatt JM, Garey JR, Shultz JW. Ecdysozoan phylogeny and Bayesian inference: first use of nearly complete 28S and 18S rRNA gene sequences to classify the arthropods and their kin. Mol Phylogenet Evol 2004; 31:178-91. [PMID: 15019618 DOI: 10.1016/j.ympev.2003.07.013] [Citation(s) in RCA: 197] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2003] [Revised: 07/18/2003] [Indexed: 10/27/2022]
Abstract
Relationships among the ecdysozoans, or molting animals, have been difficult to resolve. Here, we use nearly complete 28S+18S ribosomal RNA gene sequences to estimate the relations of 35 ecdysozoan taxa, including newly obtained 28S sequences from 25 of these. The tree-building algorithms were likelihood-based Bayesian inference and minimum-evolution analysis of LogDet-transformed distances, and hypotheses were tested wth parametric bootstrapping. Better taxonomic resolution and recovery of established taxa were obtained here, especially with Bayesian inference, than in previous parsimony-based studies that used 18S rRNA sequences (or 18S plus small parts of 28S). In our gene trees, priapulan worms represent the basal ecdysozoans, followed by nematomorphs, or nematomorphs plus nematodes, followed by Panarthropoda. Panarthropoda was monophyletic with high support, although the relationships among its three phyla (arthropods, onychophorans, tardigrades) remain uncertain. The four groups of arthropods-hexapods (insects and related forms), crustaceans, chelicerates (spiders, scorpions, horseshoe crabs), and myriapods (centipedes, millipedes, and relatives)-formed two well-supported clades: Hexapoda in a paraphyletic crustacea (Pancrustacea), and 'Chelicerata+Myriapoda' (a clade that we name 'Paradoxopoda'). Pycnogonids (sea spiders) were either chelicerates or part of the 'chelicerate+myriapod' clade, but not basal arthropods. Certain clades derived from morphological taxonomy, such as Mandibulata, Atelocerata, Schizoramia, Maxillopoda and Cycloneuralia, are inconsistent with these rRNA data. The 28S gene contained more signal than the 18S gene, and contributed to the improved phylogenetic resolution. Our findings are similar to those obtained from mitochondrial and nuclear (e.g., elongation factor, RNA polymerase, Hox) protein-encoding genes, and should revive interest in using rRNA genes to study arthropod and ecdysozoan relationships.
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Affiliation(s)
- Jon M Mallatt
- School of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA.
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Glenner H, Hansen AJ, Sørensen MV, Ronquist F, Huelsenbeck JP, Willerslev E. Bayesian Inference of the Metazoan Phylogeny. Curr Biol 2004; 14:1644-9. [PMID: 15380066 DOI: 10.1016/j.cub.2004.09.027] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2004] [Revised: 07/28/2004] [Accepted: 07/29/2004] [Indexed: 10/26/2022]
Abstract
Metazoan phylogeny remains one of evolutionary biology's major unsolved problems. Molecular and morphological data, as well as different analytical approaches, have produced highly conflicting results due to homoplasy resulting from more than 570 million years of evolution. To date, parsimony has been the only feasible combined approach but is highly sensitive to long-branch attraction. Recent development of stochastic models for discrete morphological characters and computationally efficient methods for Bayesian inference has enabled combined molecular and morphological data analysis with rigorous statistical approaches less prone to such inconsistencies. We present the first statistically founded analysis of a metazoan data set based on a combination of morphological and molecular data and compare the results with a traditional parsimony analysis. Interestingly, the Bayesian analyses demonstrate a high degree of congruence between morphological and molecular data, and both data sets contribute to the result of the combined analysis. Additionally, they resolve several irregularities obtained in previous studies and show high credibility values for controversial groups such as the ecdysozoans and lophotrochozoans. Parsimony, on the contrary, shows conflicting results, with morphology being congruent to the Bayesian results and the molecular data set producing peculiarities that are largely reflected in the combined analysis.
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Affiliation(s)
- Henrik Glenner
- Department of Evolutionary Biology, Biological Institute, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen, Denmark
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Todaro MA, Rocha CEF. Diversity and distribution of marine Gastrotricha along the northern beaches of the state of São Paulo (Brazil), with description of a new species ofMacrodasys(Macrodasyida, Macrodasyidae). J NAT HIST 2004. [DOI: 10.1080/0022293031000156169] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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30
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Simonetta AM. Are the traditional classes of arthropods natural ones? Recent advances in palaeontology and some considerations on morphology. ACTA ACUST UNITED AC 2004. [DOI: 10.1080/11250000409356579] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Giribet G. Molecules, development and fossils in the study of metazoan evolution; Articulata versus Ecdysozoa revisited. ZOOLOGY 2003; 106:303-26. [PMID: 16351916 DOI: 10.1078/0944-2006-00131] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Two conflicting hypotheses of protostome relationships, Articulata and Ecdysozoa, are reviewed by evaluating the evidence in favor and against each one of them. Understanding early embryonic development and segmentation in non-arthropod non-annelid protostomes seems crucial to the debate. New ways of coding metazoan matrices, avoiding ground-patterns and higher taxa, and incorporating fossil evidence seems the best way to avoid circular debates. Molecular data served as the catalyzer for the Ecdysozoa hypothesis, although morphological support had been implicitly suggested. Most molecular analyses published so far have shown some support for Ecdysozoa, whereas none has ever supported Articulata. Here, new analyses of up to four nuclear loci, including 18S rRNA, myosin heavy chain II, histone H3 and elongation factor 1-alpha are conducted to test the molecular support for Ecdysozoa, and, at least under some parameter sets, most data sets show a clade formed by the molting animals. In contrast, support for Articulata is not found under any analytical conditions.
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Affiliation(s)
- Gonzalo Giribet
- Museum of Comparative Zoology, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
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Mallatt J, Winchell CJ. Testing the new animal phylogeny: first use of combined large-subunit and small-subunit rRNA gene sequences to classify the protostomes. Mol Biol Evol 2002; 19:289-301. [PMID: 11861888 DOI: 10.1093/oxfordjournals.molbev.a004082] [Citation(s) in RCA: 188] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Although the small-subunit ribosomal RNA (SSU rRNA) gene is widely used in the molecular systematics, few large-subunit (LSU) rRNA gene sequences are known from protostome animals, and the value of the LSU gene for invertebrate systematics has not been explored. The goal of this study is to test whether combined LSU and SSU rRNA gene sequences support the division of protostomes into Ecdysozoa (molting forms) and Lophotrochozoa, as was proposed by Aguinaldo et al. (1997) (Nature 387:489) based on SSU rRNA sequences alone. Nearly complete LSU gene sequences were obtained, and combined LSU + SSU sequences were assembled, for 15 distantly related protostome taxa plus five deuterostome outgroups. When the aligned LSU + SSU sequences were analyzed by tree-building methods (minimum evolution analysis of LogDet-transformed distances, maximum likelihood, and maximum parsimony) and by spectral analysis of LogDet distances, both Ecdysozoa and Lophotrochozoa were indeed strongly supported (e.g., bootstrap values >90%), with higher support than from the SSU sequences alone. Furthermore, with the LogDet-based methods, the LSU + SSU sequences resolved some accepted subgroups within Ecdysozoa and Lophotrochozoa (e.g., the polychaete sequence grouped with the echiuran, and the annelid sequences grouped with the mollusc and lophophorates)-subgroups that SSU-based studies do not reveal. Also, the mollusc sequence grouped with the sequences from lophophorates (brachiopod and phoronid). Like SSU sequences, our LSU + SSU sequences contradict older hypotheses that grouped annelids with arthropods as Articulata, that said flatworms and nematodes were basal bilateralians, and considered lophophorates, nemerteans, and chaetognaths to be deuterostomes. The position of chaetognaths within protostomes remains uncertain: our chaetognath sequence associated with that of an onychophoran, but this was unstable and probably artifactual. Finally, the benefits of combining LSU with SSU sequences for phylogenetic analyses are discussed: LSU adds signal, it can be used at lower taxonomic levels, and its core region is easy to align across distant taxa-but its base frequencies tend to be nonstationary across such taxa. We conclude that molecular systematists should use combined LSU + SSU rRNA genes rather than SSU alone.
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Affiliation(s)
- Jon Mallatt
- School of Biological Sciences, Washington State University, Pullman, WA 99164-4236, USA.
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