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Hikosaka-Katayama T, Watanuki N, Niiho S, Hikosaka A. Geographical Distribution and Genetic Diversity of Praesagittifera naikaiensis ( Acoelomorpha) in the Seto Inland Sea, Japan. Zoolog Sci 2021; 37:314-322. [PMID: 32729709 DOI: 10.2108/zs190119] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Accepted: 03/25/2020] [Indexed: 11/17/2022]
Abstract
Acoel flatworms are simple bilaterians that lack digestive lumens and coelomic cavities. Although they are a significant taxon for evaluating the evolution of metazoans, suitable species for biological experiments are not available in Japan. We recently focused on Praesagittifera naikaiensis, which inhabits the sandy shores of intertidal zones in the Seto Inland Sea in Japan, as a candidate for a representative acoel species to be used in experiments. However, reports on its distribution range remain limited. Here, we surveyed the habitats of P. naikaiensis on 108 beaches along the Seto Inland Sea. Praesagittifera naikaiensis is reported here from 37 sites (six previously known and 31 newly discovered sites) spread over a wide area of the Seto Inland Sea, from Awaji Island in Hyogo Prefecture to Fukuoka Prefecture (364 km direct distance). Based on the mitochondrial cytochrome oxidase subunit I (COI) gene haplotypes, we evaluated the genetic diversity of 145 individuals collected from 33 sites. Out of 42 COI haplotypes, 13 haplotypes were shared by multiple individuals. The most frequent haplotype was observed in 67 individuals collected from 31 sites. Eight other haplotypes were detected at geographically distant locations (maximum of 299 km direct distance). Multiple haplotypes were found at 32 sites. These results demonstrate that sufficient genetic flow exists among P. naikaiensis populations throughout the Seto Inland Sea. Molecular phylogenetic analysis of the COI haplotypes of P. naikaiensis revealed that all specimens were grouped into one clade. The genetic homogeneity of the animals in this area favors their use as an experimental animal.
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Affiliation(s)
- Tomoe Hikosaka-Katayama
- Center for Gene Science, Hiroshima University, 1-4-2 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8527, Japan
| | - Nanami Watanuki
- Faculty of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8521, Japan
| | - Saki Niiho
- Faculty of Integrated Arts and Sciences, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8521, Japan
| | - Akira Hikosaka
- Graduate School of Integrated Sciences for Life, Hiroshima University, 1-7-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8521, Japan,
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Philippe H, Poustka AJ, Chiodin M, Hoff KJ, Dessimoz C, Tomiczek B, Schiffer PH, Müller S, Domman D, Horn M, Kuhl H, Timmermann B, Satoh N, Hikosaka-Katayama T, Nakano H, Rowe ML, Elphick MR, Thomas-Chollier M, Hankeln T, Mertes F, Wallberg A, Rast JP, Copley RR, Martinez P, Telford MJ. Mitigating Anticipated Effects of Systematic Errors Supports Sister-Group Relationship between Xen acoelomorpha and Ambulacraria. Curr Biol 2019; 29:1818-1826.e6. [PMID: 31104936 DOI: 10.1016/j.cub.2019.04.009] [Citation(s) in RCA: 75] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Revised: 03/19/2019] [Accepted: 04/03/2019] [Indexed: 01/21/2023]
Abstract
Xenoturbella and the acoelomorph worms (Xenacoelomorpha) are simple marine animals with controversial affinities. They have been placed as the sister group of all other bilaterian animals (Nephrozoa hypothesis), implying their simplicity is an ancient characteristic [1, 2]; alternatively, they have been linked to the complex Ambulacraria (echinoderms and hemichordates) in a clade called the Xenambulacraria [3-5], suggesting their simplicity evolved by reduction from a complex ancestor. The difficulty resolving this problem implies the phylogenetic signal supporting the correct solution is weak and affected by inadequate modeling, creating a misleading non-phylogenetic signal. The idea that the Nephrozoa hypothesis might be an artifact is prompted by the faster molecular evolutionary rate observed within the Acoelomorpha. Unequal rates of evolution are known to result in the systematic artifact of long branch attraction, which would be predicted to result in an attraction between long-branch acoelomorphs and the outgroup, pulling them toward the root [6]. Other biases inadequately accommodated by the models used can also have strong effects, exacerbated in the context of short internal branches and long terminal branches [7]. We have assembled a large and informative dataset to address this problem. Analyses designed to reduce or to emphasize misleading signals show the Nephrozoa hypothesis is supported under conditions expected to exacerbate errors, and the Xenambulacraria hypothesis is preferred in conditions designed to reduce errors. Our reanalyses of two other recently published datasets [1, 2] produce the same result. We conclude that the Xenacoelomorpha are simplified relatives of the Ambulacraria.
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Nakano H, Miyazawa H, Maeno A, Shiroishi T, Kakui K, Koyanagi R, Kanda M, Satoh N, Omori A, Kohtsuka H. A new species of Xenoturbella from the western Pacific Ocean and the evolution of Xenoturbella. BMC Evol Biol 2017; 17:245. [PMID: 29249199 PMCID: PMC5733810 DOI: 10.1186/s12862-017-1080-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Accepted: 11/16/2017] [Indexed: 12/13/2022] Open
Abstract
BACKGROUND Xenoturbella is a group of marine benthic animals lacking an anus and a centralized nervous system. Molecular phylogenetic analyses group the animal together with the Acoelomorpha, forming the Xenacoelomorpha. This group has been suggested to be either a sister group to the Nephrozoa or a deuterostome, and therefore it may provide important insights into origins of bilaterian traits such as an anus, the nephron, feeding larvae and centralized nervous systems. However, only five Xenoturbella species have been reported and the evolutionary history of xenoturbellids and Xenacoelomorpha remains obscure. RESULTS Here we describe a new Xenoturbella species from the western Pacific Ocean, and report a new xenoturbellid structure - the frontal pore. Non-destructive microCT was used to investigate the internal morphology of this soft-bodied animal. This revealed the presence of a frontal pore that is continuous with the ventral glandular network and which exhibits similarities with the frontal organ in acoelomorphs. CONCLUSIONS Our results suggest that large size, oval mouth, frontal pore and ventral glandular network may be ancestral features for Xenoturbella. Further studies will clarify the evolutionary relationship of the frontal pore and ventral glandular network of xenoturbellids and the acoelomorph frontal organ. One of the habitats of the newly identified species is easily accessible from a marine station and so this species promises to be valuable for research on bilaterian and deuterostome evolution.
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Affiliation(s)
- Hiroaki Nakano
- Shimoda Marine Research Center, University of Tsukuba, 5-10-1, Shimoda, Shizuoka, 415-0025, Japan.
| | - Hideyuki Miyazawa
- Shimoda Marine Research Center, University of Tsukuba, 5-10-1, Shimoda, Shizuoka, 415-0025, Japan
| | - Akiteru Maeno
- Mammalian Genetics Laboratory, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka, 411-8540, Japan
| | - Toshihiko Shiroishi
- Mammalian Genetics Laboratory, National Institute of Genetics, 1111 Yata, Mishima, Shizuoka, 411-8540, Japan
| | - Keiichi Kakui
- Faculty of Science, Hokkaido University, N10 W8, Kita-ku, Sapporo, Hokkaido, 060-0810, Japan
| | - Ryo Koyanagi
- DNA Sequencing Section, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, 904-0495, Japan
| | - Miyuki Kanda
- DNA Sequencing Section, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, 904-0495, Japan
| | - Noriyuki Satoh
- Marine Genomics Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, 904-0495, Japan
| | - Akihito Omori
- Misaki Marine Biological Station, The University of Tokyo, 1024 Koajiro, Misaki, Miura, Kanagawa, 238-0225, Japan.,Present address: Sado Marine Biological Station, Faculty of Science, Niigata University, Sado, Niigata, 952-2135, Japan
| | - Hisanori Kohtsuka
- Misaki Marine Biological Station, The University of Tokyo, 1024 Koajiro, Misaki, Miura, Kanagawa, 238-0225, Japan
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Perea-Atienza E, Gavilán B, Chiodin M, Abril JF, Hoff KJ, Poustka AJ, Martinez P. The nervous system of Xen acoelomorpha: a genomic perspective. ACTA ACUST UNITED AC 2015; 218:618-28. [PMID: 25696825 DOI: 10.1242/jeb.110379] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Xenacoelomorpha is, most probably, a monophyletic group that includes three clades: Acoela, Nemertodermatida and Xenoturbellida. The group still has contentious phylogenetic affinities; though most authors place it as the sister group of the remaining bilaterians, some would include it as a fourth phylum within the Deuterostomia. Over the past few years, our group, along with others, has undertaken a systematic study of the microscopic anatomy of these worms; our main aim is to understand the structure and development of the nervous system. This research plan has been aided by the use of molecular/developmental tools, the most important of which has been the sequencing of the complete genomes and transcriptomes of different members of the three clades. The data obtained has been used to analyse the evolutionary history of gene families and to study their expression patterns during development, in both space and time. A major focus of our research is the origin of 'cephalized' (centralized) nervous systems. How complex brains are assembled from simpler neuronal arrays has been a matter of intense debate for at least 100 years. We are now tackling this issue using Xenacoelomorpha models. These represent an ideal system for this work because the members of the three clades have nervous systems with different degrees of cephalization; from the relatively simple sub-epithelial net of Xenoturbella to the compact brain of acoels. How this process of 'progressive' cephalization is reflected in the genomes or transcriptomes of these three groups of animals is the subject of this paper.
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Affiliation(s)
- Elena Perea-Atienza
- Departament de Genètica, Universitat de Barcelona, Av. Diagonal, 643, 08028-Barcelona, Catalonia, Spain
| | - Brenda Gavilán
- Departament de Genètica, Universitat de Barcelona, Av. Diagonal, 643, 08028-Barcelona, Catalonia, Spain
| | - Marta Chiodin
- Departament de Genètica, Universitat de Barcelona, Av. Diagonal, 643, 08028-Barcelona, Catalonia, Spain
| | - Josep F Abril
- Departament de Genètica, Universitat de Barcelona, Av. Diagonal, 643, 08028-Barcelona, Catalonia, Spain Institut de Biomedicina de la Universitat de Barcelona (IBUB), Av. Diagonal, 643, 08028 Barcelona, Catalonia, Spain
| | - Katharina J Hoff
- Ernst Morith Arndt University of Greifswald, Institute for Mathematics and Computer Science, Walther-Rathenau-Str. 47, 17487 Greifswald, Germany
| | - Albert J Poustka
- Dahlem Centre for Genome Research and Medical Systems Biology, Evolutionary and Environmental Genomics Group, Fabeckstraße 60-62, 14195 Berlin, Germany
| | - Pedro Martinez
- Departament de Genètica, Universitat de Barcelona, Av. Diagonal, 643, 08028-Barcelona, Catalonia, Spain Institució Catalana de Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys, 23 08010 Barcelona, Catalonia, Spain
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Abstract
Xenoturbella is a strange marine worm that can be collected regularly only off the west coast of Sweden. Due to its simple morphology, which lacks a centralized nervous system, coelom, anus, or reproductive organs, its phylogenetic position has long remained obscure. Recent phylogenomic analyses suggest it forms a new phylum, Xenacoelomorpha, together with the Acoelomorpha, but the position of the phylum remains undecided, either as a deuterostome or an early branching bilaterian. Developmental stages exhibit many phylogenetically decisive characters in various animal species, but have remained a mystery for Xenoturbella until recently. Observations of its development showed it has direct development with a very short and simple swimming stage, and that it lacks a feeding larva. Asexual reproduction has never been reported. It has been suggested that Xenoturbella feeds specifically on bivalves, but it still remains unknown whether it feeds on sperm, eggs, larvae, juveniles, carcass, mucus, or feces of bivalves, and direct observations of Xenoturbella feeding on bivalves have not been reported. Endosymbiont bacteria have been found, and their functions are being investigated. The evolutionary scenario of this taxon remains the subject of debate, and our understanding will depend largely on determining its phylogeny. Thus, although recent studies have uncovered many new and crucial facts regarding Xenoturbella, some fundamental biological information, such as phylogeny, complete life cycle, and genome, remain unsolved. Further research on the well-studied Swedish Xenoturbella bocki, as well as the discovery of new species elsewhere, are necessary if we are to more fully understand the nature of Xenoturbella.
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Affiliation(s)
- Hiroaki Nakano
- Shimoda Marine Research Center, University of Tsukuba, 5-10-1, Shimoda, Shizuoka, 415-0025 Japan
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Børve A, Hejnol A. Development and juvenile anatomy of the nemertodermatid Meara stichopi (Bock) Westblad 1949 ( Acoelomorpha). Front Zool 2014; 11:50. [PMID: 25024737 PMCID: PMC4094782 DOI: 10.1186/1742-9994-11-50] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2014] [Accepted: 07/03/2014] [Indexed: 11/17/2022] Open
Abstract
Introduction Nemertodermatida is the sister group of the Acoela, which together form the Acoelomorpha, a taxon that comprises bilaterally symmetric, small aquatic worms. While there are several descriptions of the embryology of acoel species, descriptions of nemertodermatid development are scarce. To be able to reconstruct the ground pattern of the Acoelomorpha it is crucial to gain more information about the development of several nemertodermatid species. Here we describe the development of the nemertodermatid Meara stichopi using light and fluorescent microscopic methods. Results We have collected Meara stichopi during several seasons and reconstruct the complex annual reproductive cycle dependent on the sea cucumber Parastichopus tremulus. Using common fluorescent markers for musculature (BODIPY FL-phallacidin) and neurons (antibodies against FMRFamide, serotonin, tyrosinated-tubulin) and live imaging techniques, we followed embryogenesis which takes approximately 9–10 weeks. The cleavage pattern is stereotypic up to the 16-cell stage. Ring- and longitudinal musculature start to develop during week 6, followed by the formation of the basiepidermal nervous system. The juvenile is hatching without mouth opening and has a basiepidermal nerve net with two dorsal neurite bundles and an anterior condensation. Conclusions The development of Meara stichopi differs from the development of Acoela in that it is less stereotypic and does not follow the typical acoel duet cleavage program. During late development Meara stichopi does not show a temporal anterior to posterior gradient during muscle and nervous system formation.
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Affiliation(s)
- Aina Børve
- Sars International Centre for Marine Molecular Biology, University of Bergen, Thormøhlensgate 55, 5008 Bergen, Norway
| | - Andreas Hejnol
- Sars International Centre for Marine Molecular Biology, University of Bergen, Thormøhlensgate 55, 5008 Bergen, Norway
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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: 47] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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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