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Gainett G, Klementz BC, Setton EVW, Simian C, Iuri HA, Edgecombe GD, Peretti AV, Sharma PP. A plurality of morphological characters need not equate with phylogenetic accuracy: A rare genomic change refutes the placement of Solifugae and Pseudoscorpiones in Haplocnemata. Evol Dev 2024; 26:e12467. [PMID: 38124251 DOI: 10.1111/ede.12467] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Revised: 11/28/2023] [Accepted: 12/04/2023] [Indexed: 12/23/2023]
Abstract
Recent advances in higher-level invertebrate phylogeny have leveraged shared features of genomic architecture to resolve contentious nodes across the tree of life. Yet, the interordinal relationships within Chelicerata have remained recalcitrant given competing topologies in recent molecular analyses. As such, relationships between topologically unstable orders remain supported primarily by morphological cladistic analyses. Solifugae, one such unstable chelicerate order, has long been thought to be the sister group of Pseudoscorpiones, forming the clade Haplocnemata, on the basis of eight putative morphological synapomorphies. The discovery, however, of a shared whole genome duplication placing Pseudoscorpiones in Arachnopulmonata provides the opportunity for a simple litmus test evaluating the validity of Haplocnemata. Here, we present the first developmental transcriptome of a solifuge (Titanopuga salinarum) and survey copy numbers of the homeobox genes for evidence of systemic duplication. We find that over 70% of the identified homeobox genes in T. salinarum are retained in a single copy, while representatives of the arachnopulmonates retain orthologs of those genes as two or more copies. Our results refute the placement of Solifugae in Haplocnemata. Subsequent reevaluation of putative interordinal morphological synapomorphies among chelicerates reveals a high incidence of homoplasy, reversals, and inaccurate coding within Haplocnemata and other small clades, as well as Arachnida more broadly, suggesting existing morphological character matrices are insufficient to resolve chelicerate phylogeny.
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Affiliation(s)
- Guilherme Gainett
- Department of Integrative Biology, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Benjamin C Klementz
- Department of Integrative Biology, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Emily V W Setton
- Department of Integrative Biology, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Catalina Simian
- Departamento de Diversidad Biológica y Ecología, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Córdoba, Argentina
- Laboratorio de Biología Reproductiva y Evolución, Consejo Nacional de Investigaciones Científicas Técnicas (CONICET), Instituto de Diversidad y Ecología Animal (IDEA), Córdoba, Argentina
| | - Hernán A Iuri
- División de Aracnología, Museo Argentino de Ciencias Naturales "Bernardino Rivadavia", Buenos Aires, Argentina
| | - Gregory D Edgecombe
- Department of Earth Sciences, Division ES Invertebrates and Plants Palaeobiology, The Natural History Museum, London, UK
| | - Alfredo V Peretti
- Departamento de Diversidad Biológica y Ecología, Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, Córdoba, Argentina
- Laboratorio de Biología Reproductiva y Evolución, Consejo Nacional de Investigaciones Científicas Técnicas (CONICET), Instituto de Diversidad y Ecología Animal (IDEA), Córdoba, Argentina
| | - Prashant P Sharma
- Department of Integrative Biology, University of Wisconsin-Madison, Madison, Wisconsin, USA
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Klementz BC, Brenneis G, Hinne IA, Laumer EM, Neu SM, Hareid GM, Gainett G, Setton EVW, Simian C, Vrech DE, Joyce I, Barnett AA, Patel NH, Harvey MS, Peretti AV, Gulia-Nuss M, Sharma PP. A novel expression domain of extradenticle underlies the evolutionary developmental origin of the chelicerate patella. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.05.16.594547. [PMID: 38826321 PMCID: PMC11142128 DOI: 10.1101/2024.05.16.594547] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2024]
Abstract
Neofunctionalization of duplicated gene copies is thought to be an important process underlying the origin of evolutionary novelty and provides an elegant mechanism for the origin of new phenotypic traits. One putative case where a new gene copy has been linked to a novel morphological trait is the origin of the arachnid patella, a taxonomically restricted leg segment. In spiders, the origin of this segment has been linked to the origin of the paralog dachshund-2 , suggesting that a new gene facilitated the expression of a new trait. However, various arachnid groups that possess patellae do not have a copy of dachshund-2 , disfavoring the direct link between gene origin and trait origin. We investigated the developmental genetic basis for patellar patterning in the harvestman Phalangium opilio , which lacks dachshund-2 . Here, we show that the harvestman patella is established by a novel expression domain of the transcription factor extradenticle . Leveraging this definition of patellar identity, we surveyed targeted groups across chelicerate phylogeny to assess when this trait evolved. We show that a patellar homolog is present in Pycnogonida (sea spiders) and various arachnid orders, suggesting a single origin of the patella in the ancestor of Chelicerata. A potential loss of the patella is observed in Ixodida. Our results suggest that the modification of an ancient gene, rather than the neofunctionalization of a new gene copy, underlies the origin of the patella. Broadly, this work underscores the value of comparative data and broad taxonomic sampling when testing hypotheses in evolutionary developmental biology.
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Wanninger A. Hox, homology, and parsimony: An organismal perspective. Semin Cell Dev Biol 2024; 152-153:16-23. [PMID: 36670036 DOI: 10.1016/j.semcdb.2023.01.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2022] [Revised: 11/21/2022] [Accepted: 01/08/2023] [Indexed: 01/20/2023]
Abstract
Hox genes are important regulators in animal development. They often show a mosaic of conserved (e.g., longitudinal axis patterning) and lineage-specific novel functions (e.g., development of skeletal, sensory, or locomotory systems). Despite extensive research over the past decades, it remains controversial at which node in the animal tree of life the Hox cluster evolved. Its presence already in the last common metazoan ancestor has been proposed, although the genomes of both putative earliest extant metazoan offshoots, the ctenophores and the poriferans, are devoid of Hox sequences. The lack of Hox genes in the supposedly "simple"-built poriferans and their low number in cnidarians and the basally branching bilaterians, the xenacoelomorphs, seems to support the classical notion that the number of Hox genes is correlated with the degree of animal complexity. However, the 4-fold increase of the Hox cluster in xiphosurans, a basally branching chelicerate clade, as well as the situation in some teleost fishes that show a multitude of Hox genes compared to, e.g., human, demonstrates, that there is no per se direct correlation between organismal complexity and Hox number. Traditional approaches have tried to base homology on the morphological level on shared expression profiles of individual genes, but recent data have shown that, in particular with respect to Hox and other regulatory genes, complex gene-gene interactions rather than expression signatures of individual genes alone are responsible for shaping morphological traits during ontogeny. Accordingly, for sound homology assessments and reconstructions of character evolution on organ system level, additional independent datasets (e.g., morphological, developmental) need to be included in any such analyses. If supported by solid data, proposed structural homology should be regarded as valid and not be rejected solely on the grounds of non-parsimonious distribution of the character over a given phylogenetic topology.
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Affiliation(s)
- Andreas Wanninger
- University of Vienna, Department of Evolutionary Biology, Unit for Integrative Zoology, Djerassiplatz 1, 1030 Vienna, Austria.
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Sharma PP. The Impact of Whole Genome Duplication on the Evolution of the Arachnids. Integr Comp Biol 2023; 63:825-842. [PMID: 37263789 DOI: 10.1093/icb/icad050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Revised: 05/23/2023] [Accepted: 05/26/2023] [Indexed: 06/03/2023] Open
Abstract
The proliferation of genomic resources for Chelicerata in the past 10 years has revealed that the evolution of chelicerate genomes is more dynamic than previously thought, with multiple waves of ancient whole genome duplications affecting separate lineages. Such duplication events are fascinating from the perspective of evolutionary history because the burst of new gene copies associated with genome duplications facilitates the acquisition of new gene functions (neofunctionalization), which may in turn lead to morphological novelties and spur net diversification. While neofunctionalization has been invoked in several contexts with respect to the success and diversity of spiders, the overall impact of whole genome duplications on chelicerate evolution and development remains imperfectly understood. The purpose of this review is to examine critically the role of whole genome duplication on the diversification of the extant arachnid orders, as well as assess functional datasets for evidence of subfunctionalization or neofunctionalization in chelicerates. This examination focuses on functional data from two focal model taxa: the spider Parasteatoda tepidariorum, which exhibits evidence for an ancient duplication, and the harvestman Phalangium opilio, which exhibits an unduplicated genome. I show that there is no evidence that taxa with genome duplications are more successful than taxa with unduplicated genomes. I contend that evidence for sub- or neofunctionalization of duplicated developmental patterning genes in spiders is indirect or fragmentary at present, despite the appeal of this postulate for explaining the success of groups like spiders. Available expression data suggest that the condition of duplicated Hox modules may have played a role in promoting body plan disparity in the posterior tagma of some orders, such as spiders and scorpions, but functional data substantiating this postulate are critically missing. Spatiotemporal dynamics of duplicated transcription factors in spiders may represent cases of developmental system drift, rather than neofunctionalization. Developmental system drift may represent an important, but overlooked, null hypothesis for studies of paralogs in chelicerate developmental biology. To distinguish between subfunctionalization, neofunctionalization, and developmental system drift, concomitant establishment of comparative functional datasets from taxa exhibiting the genome duplication, as well as those that lack the paralogy, is sorely needed.
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Affiliation(s)
- Prashant P Sharma
- Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI 53706, USA
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5
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Mitochondrial genomes provide insight into interfamilial relationships within Pycnogonida. Polar Biol 2022. [DOI: 10.1007/s00300-022-03085-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/14/2022]
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Brenneis G. The visual pathway in sea spiders (Pycnogonida) displays a simple serial layout with similarities to the median eye pathway in horseshoe crabs. BMC Biol 2022; 20:27. [PMID: 35086529 PMCID: PMC8796508 DOI: 10.1186/s12915-021-01212-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Accepted: 12/14/2021] [Indexed: 12/18/2022] Open
Abstract
BACKGROUND Phylogenomic studies over the past two decades have consolidated the major branches of the arthropod tree of life. However, especially within the Chelicerata (spiders, scorpions, and kin), interrelationships of the constituent taxa remain controversial. While sea spiders (Pycnogonida) are firmly established as sister group of all other extant representatives (Euchelicerata), euchelicerate phylogeny itself is still contested. One key issue concerns the marine horseshoe crabs (Xiphosura), which recent studies recover either as sister group of terrestrial Arachnida or nested within the latter, with significant impact on postulated terrestrialization scenarios and long-standing paradigms of ancestral chelicerate traits. In potential support of a nested placement, previous neuroanatomical studies highlighted similarities in the visual pathway of xiphosurans and some arachnopulmonates (scorpions, whip scorpions, whip spiders). However, contradictory descriptions of the pycnogonid visual system hamper outgroup comparison and thus character polarization. RESULTS To advance the understanding of the pycnogonid brain and its sense organs with the aim of elucidating chelicerate visual system evolution, a wide range of families were studied using a combination of micro-computed X-ray tomography, histology, dye tracing, and immunolabeling of tubulin, the neuropil marker synapsin, and several neuroactive substances (including histamine, serotonin, tyrosine hydroxylase, and orcokinin). Contrary to previous descriptions, the visual system displays a serial layout with only one first-order visual neuropil connected to a bilayered arcuate body by catecholaminergic interneurons. Fluorescent dye tracing reveals a previously reported second visual neuropil as the target of axons from the lateral sense organ instead of the eyes. CONCLUSIONS Ground pattern reconstruction reveals remarkable neuroanatomical stasis in the pycnogonid visual system since the Ordovician or even earlier. Its conserved layout exhibits similarities to the median eye pathway in euchelicerates, especially in xiphosurans, with which pycnogonids share two median eye pairs that differentiate consecutively during development and target one visual neuropil upstream of the arcuate body. Given multiple losses of median and/or lateral eyes in chelicerates, and the tightly linked reduction of visual processing centers, interconnections between median and lateral visual neuropils in xiphosurans and arachnopulmonates are critically discussed, representing a plausible ancestral condition of taxa that have retained both eye types.
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Affiliation(s)
- Georg Brenneis
- Universität Greifswald, Zoologisches Institut und Museum, AG Cytologie und Evolutionsbiologie, Soldmannstraße 23, 17489, Greifswald, Germany.
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Cotoras DD, Castanheira PDS, Sharma PP. Implications of a cheliceral axial duplication in Tetragnatha versicolor (Araneae: Tetragnathidae) for arachnid deuterocerebral appendage development. Dev Genes Evol 2021; 231:131-139. [PMID: 34125284 DOI: 10.1007/s00427-021-00678-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2021] [Accepted: 06/04/2021] [Indexed: 11/29/2022]
Abstract
The homology of the arachnid chelicera with respect to other head appendages in Panarthropoda has long been debated. Gene expression data and the re-interpretation of early transitional fossils have supported the homology of the deutocerebrum and its associated appendages, implying a homology between primary antennae (mandibulates), chelicerae (euchelicerates), and chelifores (sea spiders). Nevertheless, comparatively little is known about the mechanistic basis of proximo-distal (PD) axis induction in chelicerates, much less the basis for cheliceral fate specification. Here, we describe a new cheliceral teratology in the spider Tetragnatha versicolor Walckenaer, 1841, which consists on a duplication of the PD axis of the left chelicera associated with a terminal secondary schistomely on the fang of the lower axis. This duplication offers clues as to potential shared mechanisms of PD axis formation in the chelicera. We review the state of knowledge on PD axis induction mechanisms in arthropods and identify elements of gene regulatory networks that are key for future functional experiments of appendage development in non-insect model systems. Such investigations would allow a better understanding of PD axis induction of modified and poorly studied arthropod limbs (e.g., chelicerae, chelifores, and ovigers).
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Affiliation(s)
- Darko D Cotoras
- Entomology Department, California Academy of Sciences, 55 Music Concourse Dr., Golden Gate Park, San Francisco, CA, 94118, USA.
| | - Pedro de S Castanheira
- Laboratório de Diversidade de Aracnídeos, Universidade do Brasil/Universidade Federal do Rio de Janeiro, Av. Carlos Chagas Filho 373, 21941-902, Ilha do Fundão, Rio de Janeiro, Brazil.,Harry Butler Institute, Murdoch University, 90 South St, Murdoch, Western Australia, 6150, Australia
| | - Prashant P Sharma
- Department of Integrative Biology, University of Wisconsin-Madison, 441 Birge Hall, 430 Lincoln Drive, Madison, WI, 53706, USA
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Ontano AZ, Gainett G, Aharon S, Ballesteros JA, Benavides LR, Corbett KF, Gavish-Regev E, Harvey MS, Monsma S, Santibáñez-López CE, Setton EVW, Zehms JT, Zeh JA, Zeh DW, Sharma PP. Taxonomic Sampling and Rare Genomic Changes Overcome Long-Branch Attraction in the Phylogenetic Placement of Pseudoscorpions. Mol Biol Evol 2021; 38:2446-2467. [PMID: 33565584 PMCID: PMC8136511 DOI: 10.1093/molbev/msab038] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Long-branch attraction is a systematic artifact that results in erroneous groupings of fast-evolving taxa. The combination of short, deep internodes in tandem with long-branch attraction artifacts has produced empirically intractable parts of the Tree of Life. One such group is the arthropod subphylum Chelicerata, whose backbone phylogeny has remained unstable despite improvements in phylogenetic methods and genome-scale data sets. Pseudoscorpion placement is particularly variable across data sets and analytical frameworks, with this group either clustering with other long-branch orders or with Arachnopulmonata (scorpions and tetrapulmonates). To surmount long-branch attraction, we investigated the effect of taxonomic sampling via sequential deletion of basally branching pseudoscorpion superfamilies, as well as varying gene occupancy thresholds in supermatrices. We show that concatenated supermatrices and coalescent-based summary species tree approaches support a sister group relationship of pseudoscorpions and scorpions, when more of the basally branching taxa are sampled. Matrix completeness had demonstrably less influence on tree topology. As an external arbiter of phylogenetic placement, we leveraged the recent discovery of an ancient genome duplication in the common ancestor of Arachnopulmonata as a litmus test for competing hypotheses of pseudoscorpion relationships. We generated a high-quality developmental transcriptome and the first genome for pseudoscorpions to assess the incidence of arachnopulmonate-specific duplications (e.g., homeobox genes and miRNAs). Our results support the inclusion of pseudoscorpions in Arachnopulmonata (new definition), as the sister group of scorpions. Panscorpiones (new name) is proposed for the clade uniting Scorpiones and Pseudoscorpiones.
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Affiliation(s)
- Andrew Z Ontano
- Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI, USA
| | - Guilherme Gainett
- Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI, USA
| | - Shlomi Aharon
- National Natural History Collections, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Jesús A Ballesteros
- Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI, USA
| | - Ligia R Benavides
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA
| | - Kevin F Corbett
- Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI, USA
| | - Efrat Gavish-Regev
- National Natural History Collections, The Hebrew University of Jerusalem, Jerusalem, Israel
| | - Mark S Harvey
- Collections & Research, Western Australian Museum, Welshpool, WA, Australia
| | | | | | - Emily V W Setton
- Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI, USA
| | - Jakob T Zehms
- Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI, USA
| | - Jeanne A Zeh
- Department of Biology and Program in Ecology, Evolution & Conservation Biology, University of Nevada, Reno, NV, USA
| | - David W Zeh
- Department of Biology and Program in Ecology, Evolution & Conservation Biology, University of Nevada, Reno, NV, USA
| | - Prashant P Sharma
- Department of Integrative Biology, University of Wisconsin-Madison, Madison, WI, USA
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Budd GE. The origin and evolution of the euarthropod labrum. ARTHROPOD STRUCTURE & DEVELOPMENT 2021; 62:101048. [PMID: 33862532 DOI: 10.1016/j.asd.2021.101048] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Revised: 02/24/2021] [Accepted: 02/25/2021] [Indexed: 05/16/2023]
Abstract
A widely (although not universally) accepted model of arthropod head evolution postulates that the labrum, a structure seen in almost all living euarthropods, evolved from an anterior pair of appendages homologous to the frontal appendages of onychophorans. However, the implications of this model for the interpretation of fossil arthropods have not been fully integrated into reconstructions of the euarthropod stem group, which remains in a state of some disorder. Here I review the evidence for the nature and evolution of the labrum from living taxa, and reconsider how fossils should be interpreted in the light of this. Identification of the segmental identity of head appendage in fossil arthropods remains problematic, and often rests ultimately on unproven assertions. New evidence from the Cambrian stem-group euarthropod Parapeytoia is presented to suggest that an originally protocerebral appendage persisted well up into the upper stem-group of the euarthropods, which prompts a re-evaluation of widely-accepted segmental homologies and the interpretation of fossil central nervous systems. Only a protocerebral brain was implicitly present in a large part of the euarthropod stem group, and the deutocerebrum must have been a relatively late addition.
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Affiliation(s)
- Graham E Budd
- Department of Earth Sciences, Palaeobiology Programme, Uppsala University, Villavägen 16, Uppsala, SE 752 36, Sweden.
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Ballesteros JA, Setton EVW, Santibáñez-López CE, Arango CP, Brenneis G, Brix S, Corbett KF, Cano-Sánchez E, Dandouch M, Dilly GF, Eleaume MP, Gainett G, Gallut C, McAtee S, McIntyre L, Moran AL, Moran R, López-González PJ, Scholtz G, Williamson C, Woods HA, Zehms JT, Wheeler WC, Sharma PP. Phylogenomic Resolution of Sea Spider Diversification through Integration of Multiple Data Classes. Mol Biol Evol 2021; 38:686-701. [PMID: 32915961 PMCID: PMC7826184 DOI: 10.1093/molbev/msaa228] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Despite significant advances in invertebrate phylogenomics over the past decade, the higher-level phylogeny of Pycnogonida (sea spiders) remains elusive. Due to the inaccessibility of some small-bodied lineages, few phylogenetic studies have sampled all sea spider families. Previous efforts based on a handful of genes have yielded unstable tree topologies. Here, we inferred the relationships of 89 sea spider species using targeted capture of the mitochondrial genome, 56 conserved exons, 101 ultraconserved elements, and 3 nuclear ribosomal genes. We inferred molecular divergence times by integrating morphological data for fossil species to calibrate 15 nodes in the arthropod tree of life. This integration of data classes resolved the basal topology of sea spiders with high support. The enigmatic family Austrodecidae was resolved as the sister group to the remaining Pycnogonida and the small-bodied family Rhynchothoracidae as the sister group of the robust-bodied family Pycnogonidae. Molecular divergence time estimation recovered a basal divergence of crown group sea spiders in the Ordovician. Comparison of diversification dynamics with other marine invertebrate taxa that originated in the Paleozoic suggests that sea spiders and some crustacean groups exhibit resilience to mass extinction episodes, relative to mollusk and echinoderm lineages.
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Affiliation(s)
- Jesús A Ballesteros
- Department of Integrative Biology, University of Wisconsin–Madison, Madison, WI
| | - Emily V W Setton
- Department of Integrative Biology, University of Wisconsin–Madison, Madison, WI
| | | | - Claudia P Arango
- Queensland Museum, Biodiversity Program, Brisbane, QLD, Australia
| | - Georg Brenneis
- Zoologisches Institut und Museum, Cytologie und Evolutionsbiologie, Universität Greifswald, Greifswald, Germany
| | - Saskia Brix
- Senckenberg am Meer, German Centre for Marine Biodiversity Research (DZMB), c/o Biocenter Grindel (CeNak), Martin-Luther-King-Platz 3, Hamburg, Germany
| | - Kevin F Corbett
- Department of Integrative Biology, University of Wisconsin–Madison, Madison, WI
| | - Esperanza Cano-Sánchez
- Biodiversidad y Ecología Acuática, Departamento de Zoología, Facultad de Biología, Universidad de Sevilla, Sevilla, Spain
| | - Merai Dandouch
- Department of Biology, California State University-Channel Islands, Camarillo, CA
| | - Geoffrey F Dilly
- Department of Biology, California State University-Channel Islands, Camarillo, CA
| | - Marc P Eleaume
- Départment Milieux et Peuplements Aquatiques, Muséum National d’Histoire Naturelle, Paris, France
| | - Guilherme Gainett
- Department of Integrative Biology, University of Wisconsin–Madison, Madison, WI
| | - Cyril Gallut
- Institut de Systématique, Évolution, Biodiversité (ISYEB), Sorbonne Université, CNRS, Concarneau, France
| | - Sean McAtee
- Department of Biology, California State University-Channel Islands, Camarillo, CA
| | - Lauren McIntyre
- Department of Biology, California State University-Channel Islands, Camarillo, CA
| | - Amy L Moran
- Department of Biology, University of Hawai’I at Mānoa, Honolulu, HI
| | - Randy Moran
- Department of Biology, California State University-Channel Islands, Camarillo, CA
| | - Pablo J López-González
- Biodiversidad y Ecología Acuática, Departamento de Zoología, Facultad de Biología, Universidad de Sevilla, Sevilla, Spain
| | - Gerhard Scholtz
- Institut für Biologie, Vergleichende Zoologie, Humboldt-Universität zu Berlin, Berlin, Germany
| | - Clay Williamson
- Department of Biology, California State University-Channel Islands, Camarillo, CA
| | - H Arthur Woods
- Division of Biological Sciences, University of Montana, Missoula, MT
| | - Jakob T Zehms
- Department of Integrative Biology, University of Wisconsin–Madison, Madison, WI
| | - Ward C Wheeler
- Division of Invertebrate Zoology, American Museum of Natural History, New York City, NY
| | - Prashant P Sharma
- Department of Integrative Biology, University of Wisconsin–Madison, Madison, WI
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11
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Smith FW, Cumming M, Goldstein B. Analyses of nervous system patterning genes in the tardigrade Hypsibius exemplaris illuminate the evolution of panarthropod brains. EvoDevo 2018; 9:19. [PMID: 30069303 PMCID: PMC6065069 DOI: 10.1186/s13227-018-0106-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2018] [Accepted: 07/16/2018] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND Both euarthropods and vertebrates have tripartite brains. Several orthologous genes are expressed in similar regionalized patterns during brain development in both vertebrates and euarthropods. These similarities have been used to support direct homology of the tripartite brains of vertebrates and euarthropods. If the tripartite brains of vertebrates and euarthropods are homologous, then one would expect other taxa to share this structure. More generally, examination of other taxa can help in tracing the evolutionary history of brain structures. Tardigrades are an interesting lineage on which to test this hypothesis because they are closely related to euarthropods, and whether they have a tripartite brain or unipartite brain has recently been a focus of debate. RESULTS We tested this hypothesis by analyzing the expression patterns of six3, orthodenticle, pax6, unplugged, and pax2/5/8 during brain development in the tardigrade Hypsibius exemplaris-formerly misidentified as Hypsibius dujardini. These genes were expressed in a staggered anteroposterior order in H. exemplaris, similar to what has been reported for mice and flies. However, only six3, orthodenticle, and pax6 were expressed in the developing brain. Unplugged was expressed broadly throughout the trunk and posterior head, before the appearance of the nervous system. Pax2/5/8 was expressed in the developing central and peripheral nervous system in the trunk. CONCLUSION Our results buttress the conclusion of our previous study of Hox genes-that the brain of tardigrades is only homologous to the protocerebrum of euarthropods. They support a model based on fossil evidence that the last common ancestor of tardigrades and euarthropods possessed a unipartite brain. Our results are inconsistent with the hypothesis that the tripartite brain of euarthropods is directly homologous to the tripartite brain of vertebrates.
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Affiliation(s)
- Frank W. Smith
- Biology Department, University of North Florida, Jacksonville, FL USA
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC USA
| | - Mandy Cumming
- Biology Department, University of North Florida, Jacksonville, FL USA
| | - Bob Goldstein
- Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC USA
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Alexeeva N, Tamberg Y, Shunatova N. Postembryonic development of pycnogonids: A deeper look inside. ARTHROPOD STRUCTURE & DEVELOPMENT 2018. [PMID: 29524544 DOI: 10.1016/j.asd.2018.03.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Sea spiders form a small, enigmatic group of recent chelicerates, with an unusual bodyplan, oligosegmented larvae and a postembryonic development that is punctuated by many moults. To date, only a few papers examined the anatomical and ultrastructural modifications of the larvae and various instars. Here we traced both internal and external events of the whole postembryonic development in Nymphon brevirostre HODGE 1863 using histology, SEM, TEM and confocal microscopy. During postembryonic development, larvae of this species undergo massive reorganization: spinning apparatus and chelar glands disappear; larval legs redifferentiate; three new segments and the abdomen are formed with their corresponding internal organs and appendages; circulatory and reproductive systems develop anew and the digestive and the nervous systems change dramatically. The body cavity remains schizocoelic throughout development, and no traces of even transitory coeloms were found in any instar. In Nymphon brevirostre, just like in Artemia salina LINNAEUS 1758 the heart arises through differentiation of the already existing schizocoel, and thus the circulatory systems of arthropods and annelids are not homologous. We found that classical chelicerate tagmata, prosoma and opisthosoma, are inapplicable to adult pycnogonids, with the most striking difference being the fate and structure of the seventh appendage-bearing segment.
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Affiliation(s)
- Nina Alexeeva
- Department of Invertebrate Zoology, St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 199034, Russian Federation.
| | - Yuta Tamberg
- Department of Marine Science, University of Otago, 310 Castle Street, Dunedin, 9016, New Zealand
| | - Natalia Shunatova
- Department of Invertebrate Zoology, St. Petersburg State University, Universitetskaya nab. 7/9, St. Petersburg, 199034, Russian Federation
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13
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Abstract
The discovery of fossilized brains and ventral nerve cords in lower and mid-Cambrian arthropods has led to crucial insights about the evolution of their central nervous system, the segmental identity of head appendages and the early evolution of eyes and their underlying visual systems. Fundamental ground patterns of lower Cambrian arthropod brains and nervous systems correspond to the ground patterns of brains and nervous systems belonging to three of four major extant panarthropod lineages. These findings demonstrate the evolutionary stability of early neural arrangements over an immense time span. Here, we put these fossil discoveries in the context of evidence from cladistics, as well as developmental and comparative neuroanatomy, which together suggest that despite many evolved modifications of neuropil centers within arthropod brains and ganglia, highly conserved arrangements have been retained. Recent phylogenies of the arthropods, based on fossil and molecular evidence, and estimates of divergence dates, suggest that neural ground patterns characterizing onychophorans, chelicerates and mandibulates are likely to have diverged between the terminal Ediacaran and earliest Cambrian, heralding the exuberant diversification of body forms that account for the Cambrian Explosion.
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Affiliation(s)
- Nicholas J Strausfeld
- Department of Neuroscience and Center for Insect Science, University of Arizona, Tucson, AZ 85721, USA.
| | - Xiaoya Ma
- Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK; Yunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming 650091, People's Republic of China
| | - Gregory D Edgecombe
- Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK.
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14
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Setton EVW, March LE, Nolan ED, Jones TE, Cho H, Wheeler WC, Extavour CG, Sharma PP. Expression and function of spineless orthologs correlate with distal deutocerebral appendage morphology across Arthropoda. Dev Biol 2017; 430:224-236. [PMID: 28764892 DOI: 10.1016/j.ydbio.2017.07.016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Revised: 07/03/2017] [Accepted: 07/24/2017] [Indexed: 10/19/2022]
Abstract
The deutocerebral (second) head segment is putatively homologous across Arthropoda, in spite of remarkable disparity of form and function of deutocerebral appendages. In Mandibulata this segment bears a pair of sensory antennae, whereas in Chelicerata the same segment bears a pair of feeding appendages called chelicerae. Part of the evidence for the homology of deutocerebral appendages is the conserved function of homothorax (hth), which has been shown to specify antennal or cheliceral fate in the absence of Hox signaling, in both mandibulate and chelicerate exemplars. However, the genetic basis for the morphological disparity of antenna and chelicera is not understood. To test whether downstream targets of hth have diverged in a lineage-specific manner, we examined the evolution of the function and expression of spineless (ss), which in two holometabolous insects is known to act as a hth target and distal antennal determinant. Toward expanding phylogenetic representation of gene expression data, here we show that strong expression of ss is observed in developing antennae of a hemimetabolous insect, a centipede, and an amphipod crustacean. By contrast, ss orthologs are not expressed throughout the cheliceral limb buds of spiders or harvestmen during developmental stages when appendage fate is specified. RNA interference-mediated knockdown of ss in Oncopeltus fasciatus, which bears a simple plesiomorphic antenna, resulted in homeotic distal antenna-to-leg transformation, comparable to data from holometabolous insect counterparts. Knockdown of hth in Oncopeltus fasciatus abrogated ss expression, suggesting conservation of upstream regulation. These data suggest that ss may be a flagellar (distal antennal) determinant more broadly, and that this function was acquired at the base of Mandibulata.
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Affiliation(s)
- Emily V W Setton
- Department of Integrative Biology, University of Wisconsin-Madison, 430 Lincoln Drive, Madison, WI 53706, USA
| | - Logan E March
- Department of Integrative Biology, University of Wisconsin-Madison, 430 Lincoln Drive, Madison, WI 53706, USA
| | - Erik D Nolan
- Department of Integrative Biology, University of Wisconsin-Madison, 430 Lincoln Drive, Madison, WI 53706, USA
| | - Tamsin E Jones
- Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA
| | - Holly Cho
- Department of Integrative Biology, University of Wisconsin-Madison, 430 Lincoln Drive, Madison, WI 53706, USA
| | - Ward C Wheeler
- Division of Invertebrate Zoology, American Museum of Natural History, Central Park West at 79th Street, New York, NY, USA
| | - Cassandra G Extavour
- Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA; Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA
| | - Prashant P Sharma
- Department of Integrative Biology, University of Wisconsin-Madison, 430 Lincoln Drive, Madison, WI 53706, USA.
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15
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Ortega-Hernández J, Janssen R, Budd GE. Origin and evolution of the panarthropod head - A palaeobiological and developmental perspective. ARTHROPOD STRUCTURE & DEVELOPMENT 2017; 46:354-379. [PMID: 27989966 DOI: 10.1016/j.asd.2016.10.011] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2016] [Revised: 09/15/2016] [Accepted: 10/25/2016] [Indexed: 05/14/2023]
Abstract
The panarthropod head represents a complex body region that has evolved through the integration and functional specialization of the anterior appendage-bearing segments. Advances in the developmental biology of diverse extant organisms have led to a substantial clarity regarding the relationships of segmental homology between Onychophora (velvet worms), Tardigrada (water bears), and Euarthropoda (e.g. arachnids, myriapods, crustaceans, hexapods). The improved understanding of the segmental organization in panarthropods offers a novel perspective for interpreting the ubiquitous Cambrian fossil record of these successful animals. A combined palaeobiological and developmental approach to the study of the panarthropod head through deep time leads us to propose a consensus hypothesis for the intricate evolutionary history of this important tagma. The contribution of exceptionally preserved brains in Cambrian fossils - together with the recognition of segmentally informative morphological characters - illuminate the polarity for major anatomical features. The euarthropod stem-lineage provides a detailed view of the step-wise acquisition of critical characters, including the origin of a multiappendicular head formed by the fusion of several segments, and the transformation of the ancestral protocerebral limb pair into the labrum, following the postero-ventral migration of the mouth opening. Stem-group onychophorans demonstrate an independent ventral migration of the mouth and development of a multisegmented head, as well as the differentiation of the deutocerebral limbs as expressed in extant representatives. The anterior organization of crown-group Tardigrada retains several ancestral features, such as an anterior-facing mouth and one-segmented head. The proposed model aims to clarify contentious issues on the evolution of the panarthropod head, and lays the foundation from which to further address this complex subject in the future.
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Affiliation(s)
| | - Ralf Janssen
- Department of Earth Sciences, Palaeobiology, Uppsala University, Villavägen 16, Uppsala SE-752 36, Sweden
| | - Graham E Budd
- Department of Earth Sciences, Palaeobiology, Uppsala University, Villavägen 16, Uppsala SE-752 36, Sweden
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16
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Smith FW, Goldstein B. Segmentation in Tardigrada and diversification of segmental patterns in Panarthropoda. ARTHROPOD STRUCTURE & DEVELOPMENT 2017; 46:328-340. [PMID: 27725256 DOI: 10.1016/j.asd.2016.10.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Revised: 08/11/2016] [Accepted: 10/03/2016] [Indexed: 05/03/2023]
Abstract
The origin and diversification of segmented metazoan body plans has fascinated biologists for over a century. The superphylum Panarthropoda includes three phyla of segmented animals-Euarthropoda, Onychophora, and Tardigrada. This superphylum includes representatives with relatively simple and representatives with relatively complex segmented body plans. At one extreme of this continuum, euarthropods exhibit an incredible diversity of serially homologous segments. Furthermore, distinct tagmosis patterns are exhibited by different classes of euarthropods. At the other extreme, all tardigrades share a simple segmented body plan that consists of a head and four leg-bearing segments. The modular body plans of panarthropods make them a tractable model for understanding diversification of animal body plans more generally. Here we review results of recent morphological and developmental studies of tardigrade segmentation. These results complement investigations of segmentation processes in other panarthropods and paleontological studies to illuminate the earliest steps in the evolution of panarthropod body plans.
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Affiliation(s)
- Frank W Smith
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
| | - Bob Goldstein
- Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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17
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Brenneis G, Bogomolova EV, Arango CP, Krapp F. From egg to "no-body": an overview and revision of developmental pathways in the ancient arthropod lineage Pycnogonida. Front Zool 2017; 14:6. [PMID: 28191025 PMCID: PMC5297176 DOI: 10.1186/s12983-017-0192-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2016] [Accepted: 01/23/2017] [Indexed: 12/28/2022] Open
Abstract
BACKGROUND Arthropod diversity is unparalleled in the animal kingdom. The study of ontogeny is pivotal to understand which developmental processes underlie the incredible morphological disparity of arthropods and thus to eventually unravel evolutionary transformations leading to their success. Work on laboratory model organisms has yielded in-depth data on numerous developmental mechanisms in arthropods. Yet, although the range of studied taxa has increased noticeably since the advent of comparative evolutionary developmental biology (evo-devo), several smaller groups remain understudied. This includes the bizarre Pycnogonida (sea spiders) or "no-bodies", a taxon occupying a crucial phylogenetic position for the interpretation of arthropod development and evolution. RESULTS Pycnogonid development is variable at familial and generic levels and sometimes even congeneric species exhibit different developmental modes. Here, we summarize the available data since the late 19th century. We clarify and resolve terminological issues persisting in the pycnogonid literature and distinguish five developmental pathways, based on (1) type of the hatching stage, (2) developmental-morphological features during postembryonic development and (3) selected life history characteristics. Based on phylogenetic analyses and the fossil record, we discuss plausible plesiomorphic features of pycnogonid development that allow comparison to other arthropods. These features include (1) a holoblastic, irregular cleavage with equal-sized blastomeres, (2) initiation of gastrulation by a single bottle-shaped cell, (3) the lack of a morphologically distinct germ band during embryogenesis, (4) a parasitic free-living protonymphon larva as hatching stage and (5) a hemianamorphic development during the postlarval and juvenile phases. Further, we propose evolutionary developmental trajectories within crown-group Pycnogonida. CONCLUSIONS A resurgence of studies on pycnogonid postembryonic development has provided various new insights in the last decades. However, the scarcity of modern-day embryonic data - including the virtual lack of gene expression and functional studies - needs to be addressed in future investigations to strengthen comparisons to other arthropods and arthropod outgroups in the framework of evo-devo. Our review may serve as a basis for an informed choice of target species for such studies, which will not only shed light on chelicerate development and evolution but furthermore hold the potential to contribute important insights into the anamorphic development of the arthropod ancestor.
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Affiliation(s)
- Georg Brenneis
- Wellesley College, Neuroscience Program, 106 Central Street, Wellesley, MA 02481 USA
| | | | - Claudia P. Arango
- Queensland Museum, Biodiversity Program, PO Box 3300, South Brisbane, QLD 4101 Australia
| | - Franz Krapp
- Zoologisches Forschungsmuseum A. Koenig, Adenauerallee 160, D-53113 Bonn, Germany
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18
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Sharma PP, Tarazona OA, Lopez DH, Schwager EE, Cohn MJ, Wheeler WC, Extavour CG. A conserved genetic mechanism specifies deutocerebral appendage identity in insects and arachnids. Proc Biol Sci 2016; 282:20150698. [PMID: 25948691 DOI: 10.1098/rspb.2015.0698] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The segmental architecture of the arthropod head is one of the most controversial topics in the evolutionary developmental biology of arthropods. The deutocerebral (second) segment of the head is putatively homologous across Arthropoda, as inferred from the segmental distribution of the tripartite brain and the absence of Hox gene expression of this anterior-most, appendage-bearing segment. While this homology statement implies a putative common mechanism for differentiation of deutocerebral appendages across arthropods, experimental data for deutocerebral appendage fate specification are limited to winged insects. Mandibulates (hexapods, crustaceans and myriapods) bear a characteristic pair of antennae on the deutocerebral segment, whereas chelicerates (e.g. spiders, scorpions, harvestmen) bear the eponymous chelicerae. In such hexapods as the fruit fly, Drosophila melanogaster, and the cricket, Gryllus bimaculatus, cephalic appendages are differentiated from the thoracic appendages (legs) by the activity of the appendage patterning gene homothorax (hth). Here we show that embryonic RNA interference against hth in the harvestman Phalangium opilio results in homeonotic chelicera-to-leg transformations, and also in some cases pedipalp-to-leg transformations. In more strongly affected embryos, adjacent appendages undergo fusion and/or truncation, and legs display proximal defects, suggesting conservation of additional functions of hth in patterning the antero-posterior and proximo-distal appendage axes. Expression signal of anterior Hox genes labial, proboscipedia and Deformed is diminished, but not absent, in hth RNAi embryos, consistent with results previously obtained with the insect G. bimaculatus. Our results substantiate a deep homology across arthropods of the mechanism whereby cephalic appendages are differentiated from locomotory appendages.
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Affiliation(s)
- Prashant P Sharma
- Division of Invertebrate Zoology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA
| | - Oscar A Tarazona
- Department of Biology, University of Florida, Gainesville, FL 32611, USA
| | - Davys H Lopez
- Department of Biology, University of Florida, Gainesville, FL 32611, USA Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Evelyn E Schwager
- Department of Biological and Medical Sciences, Oxford Brookes University, Oxford OX3 0BP, UK
| | - Martin J Cohn
- Department of Biology, University of Florida, Gainesville, FL 32611, USA
| | - Ward C Wheeler
- Division of Invertebrate Zoology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024, USA
| | - Cassandra G Extavour
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
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19
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Ortega-Hernández J, Budd GE. The nature of non-appendicular anterior paired projections in Palaeozoic total-group Euarthropoda. ARTHROPOD STRUCTURE & DEVELOPMENT 2016; 45:185-199. [PMID: 26802876 DOI: 10.1016/j.asd.2016.01.006] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2016] [Accepted: 01/12/2016] [Indexed: 05/14/2023]
Abstract
Recent studies have clarified the segmental organization of appendicular and exoskeletal structures in the anterior region of Cambrian stem-group Euarthropoda, and thus led to better understanding of the deep evolutionary origins of the head region in this successful animal group. However, there are aspects of the anterior organization of Palaeozoic euarthropods that remain problematic, such as the morphological identity and significance of minute limb-like projections on the anterior region in stem and crown-group representatives. Here, we draw attention to topological and morphological similarities between the frontal filaments of extant Crustacea and the embryonic frontal processes of Onychophora, and distinctive anterior paired projections observed in several extinct total-group Euarthropoda. Anterior paired projections are redescribed in temporally and phylogenetically distant fossil taxa, including the gilled lobopodians Kerygmachela kierkegaardi and Pambdelurion whittingtoni, the bivalved stem-euarthropod Canadaspis perfecta, the larval pycnogonid Cambropycnogon klausmuelleri, and the mandibulate Tanazios dokeron. Developmental data supporting the homology of the 'primary antennae' of Onychophora, the 'frontal appendages' of lower-stem Euarthropoda, and the hypostome/labrum complex of Deuteropoda, argue against the morphological identity of the anterior paired projections of extant and extinct panarthropods as a pair of pre-ocular appendages. Instead, we regard the paired projections of fossil total-group euarthropods as non-appendicular evaginations with a likely protocerebral segmental association, and a possible sensorial function. The widespread occurrence of pre-ocular paired projections among extant and extinct taxa suggests their potential homology as fundamentally ancestral features of the anterior body organization in Panarthropoda. Non-appendicular paired projections with a sensorial function may reflect a critical--yet previously overlooked--component of the panarthropod ground pattern.
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Affiliation(s)
- Javier Ortega-Hernández
- Department of Earth Sciences, Downing Street, University of Cambridge, Cambridge CB2 3EQ, UK.
| | - Graham E Budd
- Department of Earth Sciences, Palaeobiology, Uppsala University, Norbyvägen 22, Uppsala SE 752 36, Sweden
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20
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The Compact Body Plan of Tardigrades Evolved by the Loss of a Large Body Region. Curr Biol 2016; 26:224-229. [DOI: 10.1016/j.cub.2015.11.059] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Revised: 11/12/2015] [Accepted: 11/12/2015] [Indexed: 01/17/2023]
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21
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Saadaoui M, Litim-Mecheri I, Macchi M, Graba Y, Maurel-Zaffran C. A survey of conservation of sea spider and Drosophila Hox protein activities. Mech Dev 2015; 138 Pt 2:73-86. [PMID: 26238019 DOI: 10.1016/j.mod.2015.07.010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Revised: 07/24/2015] [Accepted: 07/25/2015] [Indexed: 01/29/2023]
Abstract
Hox proteins have well-established functions in development and evolution, controlling the final morphology of bilaterian animals. The common phylogenetic origin of Hox proteins and the associated evolutionary diversification of protein sequences provide a unique framework to explore the relationship between changes in protein sequence and function. In this study, we aimed at questioning how sequence variation within arthropod Hox proteins influences function. This was achieved by exploring the functional impact of sequence conservation/divergence of the Hox genes, labial, Sex comb reduced, Deformed, Ultrabithorax and abdominalA from two distant arthropods, the sea spider and the well-studied Drosophila. Results highlight a correlation between sequence conservation within the homeodomain and the degree of functional conservation, and identify a novel functional domain in the Labial protein.
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Affiliation(s)
- Mehdi Saadaoui
- Aix Marseille Université, CNRS, IBDM, UMR 7288, Campus de Luminy, Marseille, cedex 09 13288, France; Institut de Biologie de l'ENS, 46, rue d'Ulm, 75005 Paris, France
| | - Isma Litim-Mecheri
- Aix Marseille Université, CNRS, IBDM, UMR 7288, Campus de Luminy, Marseille, cedex 09 13288, France; IGBMC, INSERM U964, CNRS UMR 7104, Université de Strasbourg, 67404 Illkirch, France
| | - Meiggie Macchi
- Aix Marseille Université, CNRS, IBDM, UMR 7288, Campus de Luminy, Marseille, cedex 09 13288, France
| | - Yacine Graba
- Aix Marseille Université, CNRS, IBDM, UMR 7288, Campus de Luminy, Marseille, cedex 09 13288, France
| | - Corinne Maurel-Zaffran
- Aix Marseille Université, CNRS, IBDM, UMR 7288, Campus de Luminy, Marseille, cedex 09 13288, France
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22
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Di Z, Yu Y, Wu Y, Hao P, He Y, Zhao H, Li Y, Zhao G, Li X, Li W, Cao Z. Genome-wide analysis of homeobox genes from Mesobuthus martensii reveals Hox gene duplication in scorpions. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2015; 61:25-33. [PMID: 25910680 DOI: 10.1016/j.ibmb.2015.04.002] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Revised: 04/10/2015] [Accepted: 04/12/2015] [Indexed: 06/04/2023]
Abstract
Homeobox genes belong to a large gene group, which encodes the famous DNA-binding homeodomain that plays a key role in development and cellular differentiation during embryogenesis in animals. Here, one hundred forty-nine homeobox genes were identified from the Asian scorpion, Mesobuthus martensii (Chelicerata: Arachnida: Scorpiones: Buthidae) based on our newly assembled genome sequence with approximately 248 × coverage. The identified homeobox genes were categorized into eight classes including 82 families: 67 ANTP class genes, 33 PRD genes, 11 LIM genes, five POU genes, six SINE genes, 14 TALE genes, five CUT genes, two ZF genes and six unclassified genes. Transcriptome data confirmed that more than half of the genes were expressed in adults. The homeobox gene diversity of the eight classes is similar to the previously analyzed Mandibulata arthropods. Interestingly, it is hypothesized that the scorpion M. martensii may have two Hox clusters. The first complete genome-wide analysis of homeobox genes in Chelicerata not only reveals the repertoire of scorpion, arachnid and chelicerate homeobox genes, but also shows some insights into the evolution of arthropod homeobox genes.
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Affiliation(s)
- Zhiyong Di
- College of Life Sciences, Wuhan University, Wuhan, China; College of Life Sciences, University of Science and Technology of China, Hefei, China
| | - Yao Yu
- Key Laboratory of Synthetic Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Yingliang Wu
- College of Life Sciences, Wuhan University, Wuhan, China
| | - Pei Hao
- Key Lab of Systems Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Yawen He
- College of Life Sciences, Wuhan University, Wuhan, China
| | - Huabin Zhao
- College of Life Sciences, Wuhan University, Wuhan, China
| | - Yixue Li
- Key Lab of Systems Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
| | - Guoping Zhao
- Key Laboratory of Synthetic Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Xuan Li
- Key Lab of Systems Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China.
| | - Wenxin Li
- College of Life Sciences, Wuhan University, Wuhan, China.
| | - Zhijian Cao
- College of Life Sciences, Wuhan University, Wuhan, China.
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23
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Gross V, Mayer G. Neural development in the tardigrade Hypsibius dujardini based on anti-acetylated α-tubulin immunolabeling. EvoDevo 2015; 6:12. [PMID: 26052416 PMCID: PMC4458024 DOI: 10.1186/s13227-015-0008-4] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Accepted: 04/02/2015] [Indexed: 12/15/2022] Open
Abstract
Background The tardigrades (water bears) are a cosmopolitan group of microscopic ecdysozoans found in a variety of aquatic and temporarily wet environments. They are members of the Panarthropoda (Tardigrada + Onychophora + Arthropoda), although their exact position within this group remains contested. Studies of embryonic development in tardigrades have been scarce and have yielded contradictory data. Therefore, we investigated the development of the nervous system in embryos of the tardigrade Hypsibius dujardini using immunohistochemical techniques in conjunction with confocal laser scanning microscopy in an effort to gain insight into the evolution of the nervous system in panarthropods. Results An antiserum against acetylated α-tubulin was used to visualize the axonal processes and general neuroanatomy in whole-mount embryos of the eutardigrade H. dujardini. Our data reveal that the tardigrade nervous system develops in an anterior-to-posterior gradient, beginning with the neural structures of the head. The brain develops as a dorsal, bilaterally symmetric structure and contains a single developing central neuropil. The stomodeal nervous system develops separately and includes at least four separate, ring-like commissures. A circumbuccal nerve ring arises late in development and innervates the circumoral sensory field. The segmental trunk ganglia likewise arise from anterior to posterior and establish links with each other via individual pioneering axons. Each hemiganglion is associated with a number of peripheral nerves, including a pair of leg nerves and a branched, dorsolateral nerve. Conclusions The revealed pattern of brain development supports a single-segmented brain in tardigrades and challenges previous assignments of homology between tardigrade brain lobes and arthropod brain segments. Likewise, the tardigrade circumbuccal nerve ring cannot be homologized with the arthropod ‘circumoral’ nerve ring, suggesting that this structure is unique to tardigrades. Finally, we propose that the segmental ganglia of tardigrades and arthropods are homologous and, based on these data, favor a hypothesis that supports tardigrades as the sister group of arthropods. Electronic supplementary material The online version of this article (doi:10.1186/s13227-015-0008-4) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Vladimir Gross
- Animal Evolution and Development, Institute of Biology, University of Leipzig, Talstraße 33, 04103 Leipzig, Germany ; Department of Zoology, Institute of Biology, University of Kassel, Heinrich-Plett-Str. 40, D-34132 Kassel, Germany
| | - Georg Mayer
- Department of Zoology, Institute of Biology, University of Kassel, Heinrich-Plett-Str. 40, D-34132 Kassel, Germany
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24
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Smith FW, Jockusch EL. The metameric pattern of Hypsibius dujardini(Eutardigrada) and its relationship to that of other panarthropods. Front Zool 2014. [DOI: 10.1186/s12983-014-0066-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
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Lehmann T, Heß M, Wanner G, Melzer RR. Dissecting a neuron network: FIB-SEM-based 3D-reconstruction of the visual neuropils in the sea spider Achelia langi (Dohrn, 1881) (Pycnogonida). BMC Biol 2014; 12:59. [PMID: 25285383 PMCID: PMC4159573 DOI: 10.1186/s12915-014-0059-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2014] [Accepted: 07/21/2014] [Indexed: 03/22/2024] Open
Abstract
BACKGROUND The research field of connectomics arose just recently with the development of new three-dimensional-electron microscopy (EM) techniques and increasing computing power. So far, only a few model species (for example, mouse, the nematode Caenorhabditis elegans, and the fruit fly Drosophila melanogaster) have been studied using this approach. Here, we present a first attempt to expand this circle to include pycnogonids, which hold a key position for the understanding of arthropod evolution. The visual neuropils in Achelia langi are studied using a focused ion beam-scanning electron microscope (FIB-SEM) crossbeam-workstation, and a three-dimensional serial reconstruction of the connectome is presented. RESULTS The two eyes of each hemisphere of the sea spider's eye tubercle are connected to a first and a second visual neuropil. The first visual neuropil is subdivided in two hemineuropils, each responsible for one eye and stratified into three layers. Six different neuron types postsynaptic to the retinula (R-cells) axons are characterized by their morphology: five types of descending unipolar neurons and one type of ascending neurons. These cell types are also identified by Golgi impregnations. Mapping of all identifiable chemical synapses indicates that the descending unipolar neurons are postsynaptic to the R-cells and, hence, are second-order neurons. The ascending neurons are predominantly presynaptic and sometimes postsynaptic to the R-cells and may play a feedback role. CONCLUSIONS Comparing these results with the compound eye visual system of crustaceans and insects - the only arthropod visual system studied so far in such detail - we found striking similarities in the morphology and synaptic organization of the different neuron types. Hence, the visual system of pycnogonids shows features of both chelicerate median and mandibulate lateral eyes.
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Affiliation(s)
- Tobias Lehmann
- />Bavarian State Collection of Zoology – SNSB, Münchhausenstraße 21, 81247 Munich, Germany
- />Department Biology II, Ludwig-Maximilians-Universität München, Großhaderner Straße 2, 82152 Planegg-Martinsried, Germany
| | - Martin Heß
- />Department Biology II, Ludwig-Maximilians-Universität München, Großhaderner Straße 2, 82152 Planegg-Martinsried, Germany
- />GeoBio-Center LMU, Richard-Wagner-Straße 10, 80333 Munich, Germany
| | - Gerhard Wanner
- />Department Biology I, Ludwig-Maximilians-Universität München, Großhaderner Straße 2-4, 82152 Planegg-Martinsried, Germany
| | - Roland R Melzer
- />Bavarian State Collection of Zoology – SNSB, Münchhausenstraße 21, 81247 Munich, Germany
- />Department Biology II, Ludwig-Maximilians-Universität München, Großhaderner Straße 2, 82152 Planegg-Martinsried, Germany
- />GeoBio-Center LMU, Richard-Wagner-Straße 10, 80333 Munich, Germany
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Smith FW, Angelini DR, Jockusch EL. A functional genetic analysis in flour beetles (Tenebrionidae) reveals an antennal identity specification mechanism active during metamorphosis in Holometabola. Mech Dev 2014; 132:13-27. [PMID: 24534744 DOI: 10.1016/j.mod.2014.02.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2013] [Revised: 01/13/2014] [Accepted: 02/06/2014] [Indexed: 11/27/2022]
Abstract
The antenna was the first arthropod ventral appendage to evolve non-leg identity. Models of antennal evolution have been based on comparisons of antennal and leg identity specification mechanisms in Drosophila melanogaster, a species in which appendages develop from highly derived imaginal discs during the larval period. We test for conservation of the Drosophila antennal identity specification mechanism at metamorphosis in Tribolium castaneum and three other flour beetle species (Tribolium confusum, Tribolium brevicornis and Latheticus oryzae) in the family Tenebrionidae. In Drosophila, loss of function of four transcription factors-homothorax, extradenticle, Distal-less, and spineless-causes large-scale transformations of the antenna to leg identity. Distal-less and spineless function similarly during metamorphosis in T. castaneum. RNA interference (RNAi) targeting homothorax (hth) or extradenticle (exd) caused transformation of the proximal antenna to distal leg identity in flour beetles, but did not affect the identity of the distal antenna. This differs from the functional domain of these genes in early instar Drosophila, where they are required for identity specification throughout the antenna, but matches their functional domain in late instar Drosophila. The similarities between antennal identity specification at metamorphosis in flour beetles and in late larval Drosophila likely reflect the conservation of an ancestral metamorphic developmental mechanism. There were two notable differences in hth/exd loss of function phenotypes between flies and beetles. Flour beetles retained all of their primary segments in both the antenna and legs, whereas flies undergo reduction and fusion of primary segments. This difference in ground state appendage morphology casts doubt on interpretations of developmental ground states as evolutionary atavisms. Additionally, adult Tribolium eyes were transformed to elytron-like structures; we provide a developmental hypothesis for this evolutionarily surprising transformation.
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Affiliation(s)
- Frank W Smith
- Department of Ecology & Evolutionary Biology, University of Connecticut, 75 N. Eagleville Rd., U-3043, Storrs, CT 06269-3043, USA.
| | - David R Angelini
- Department of Ecology & Evolutionary Biology, University of Connecticut, 75 N. Eagleville Rd., U-3043, Storrs, CT 06269-3043, USA; Department of Biology, Colby College, 5734 Mayflower Hill, Waterville, ME 04901, USA
| | - Elizabeth L Jockusch
- Department of Ecology & Evolutionary Biology, University of Connecticut, 75 N. Eagleville Rd., U-3043, Storrs, CT 06269-3043, USA
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Ou Q, Shu D, Mayer G. Cambrian lobopodians and extant onychophorans provide new insights into early cephalization in Panarthropoda. Nat Commun 2013; 3:1261. [PMID: 23232391 PMCID: PMC3535342 DOI: 10.1038/ncomms2272] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2012] [Accepted: 11/08/2012] [Indexed: 01/11/2023] Open
Abstract
Cambrian lobopodians are important for understanding the evolution of arthropods, but despite their soft-bodied preservation, the organization of the cephalic region remains obscure. Here we describe new material of the early Cambrian lobopodian Onychodictyon ferox from southern China, which reveals hitherto unknown head structures. These include a proboscis with a terminal mouth, an anterior arcuate sclerite, a pair of ocellus-like eyes and branched, antenniform appendages associated with this ocular segment. These findings, combined with a comparison with other lobopodians, suggest that the head of the last common ancestor of fossil lobopodians and extant panarthropods comprized a single ocular segment with a proboscis and terminal mouth. The lack of specialized mouthparts in O. ferox and the involvement of non-homologous mouthparts in onychophorans, tardigrades and arthropods argue against a common origin of definitive mouth openings among panarthropods, whereas the embryonic stomodaeum might well be homologous at least in Onychophora and Arthropoda. Lobopodians include stem-group arthropods and panarthropods, and date back to the early Cambrian. Ou et al. describe specimens of the early Cambrian lobopodian Onychodictyon ferox, revealing new head structures such as modified appendages, eyes, a terminal mouth and a sucking pharynx.
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Affiliation(s)
- Qiang Ou
- Early Life Evolution Laboratory, School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China.
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Sharma PP, Schwager EE, Giribet G, Jockusch EL, Extavour CG. Distal-lessanddachshundpattern both plesiomorphic and apomorphic structures in chelicerates: RNA interference in the harvestmanPhalangium opilio(Opiliones). Evol Dev 2013; 15:228-42. [DOI: 10.1111/ede.12029] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
| | - Evelyn E. Schwager
- Department of Organismic and Evolutionary Biology; Harvard University; 26 Oxford Street, Cambridge, MA 02138; USA
| | | | - Elizabeth L. Jockusch
- Department of Ecology and Evolutionary Biology; University of Connecticut; 75 N. Eagleville Road, Storrs, CT 06269; USA
| | - Cassandra G. Extavour
- Department of Organismic and Evolutionary Biology; Harvard University; 26 Oxford Street, Cambridge, MA 02138; USA
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29
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Mayer G, Kauschke S, Rüdiger J, Stevenson PA. Neural markers reveal a one-segmented head in tardigrades (water bears). PLoS One 2013; 8:e59090. [PMID: 23516602 PMCID: PMC3596308 DOI: 10.1371/journal.pone.0059090] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2012] [Accepted: 02/11/2013] [Indexed: 12/31/2022] Open
Abstract
BACKGROUND While recent neuroanatomical and gene expression studies have clarified the alignment of cephalic segments in arthropods and onychophorans, the identity of head segments in tardigrades remains controversial. In particular, it is unclear whether the tardigrade head and its enclosed brain comprises one, or several segments, or a non-segmental structure. To clarify this, we applied a variety of histochemical and immunocytochemical markers to specimens of the tardigrade Macrobiotus cf. harmsworthi and the onychophoran Euperipatoides rowelli. METHODOLOGY/PRINCIPAL FINDINGS Our immunolabelling against serotonin, FMRFamide and α-tubulin reveals that the tardigrade brain is a dorsal, bilaterally symmetric structure that resembles the brain of onychophorans and arthropods rather than a circumoesophageal ring typical of cycloneuralians (nematodes and allies). A suboesophageal ganglion is clearly lacking. Our data further reveal a hitherto unknown, unpaired stomatogastric ganglion in Macrobiotus cf. harmsworthi, which innervates the ectodermal oesophagus and the endodermal midgut and is associated with the second leg-bearing segment. In contrast, the oesophagus of the onychophoran E. rowelli possesses no immunoreactive neurons, whereas scattered bipolar, serotonin-like immunoreactive cell bodies are found in the midgut wall. Furthermore, our results show that the onychophoran pharynx is innervated by a medullary loop nerve accompanied by monopolar, serotonin-like immunoreactive cell bodies. CONCLUSIONS/SIGNIFICANCE A comparison of the nervous system innervating the foregut and midgut structures in tardigrades and onychophorans to that of arthropods indicates that the stomatogastric ganglion is a potential synapomorphy of Tardigrada and Arthropoda. Its association with the second leg-bearing segment in tardigrades suggests that the second trunk ganglion is a homologue of the arthropod tritocerebrum, whereas the first ganglion corresponds to the deutocerebrum. We therefore conclude that the tardigrade brain consists of a single segmental region corresponding to the arthropod protocerebrum and, accordingly, that the tardigrade head is a non-composite, one-segmented structure.
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Affiliation(s)
- Georg Mayer
- Animal Evolution and Development, Institute of Biology, University of Leipzig, Leipzig, Germany.
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Briggs DEG, Siveter DJ, Siveter DJ, Sutton MD, Garwood RJ, Legg D. Silurian horseshoe crab illuminates the evolution of arthropod limbs. Proc Natl Acad Sci U S A 2012; 109:15702-5. [PMID: 22967511 PMCID: PMC3465403 DOI: 10.1073/pnas.1205875109] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The basic arrangement of limbs in euarthropods consists of a uniramous head appendage followed by a series of biramous appendages. The body is divided into functional units or tagmata which are usually distinguished by further differentiation of the limbs. The living horseshoe crabs are remnants of a much larger diversity of aquatic chelicerates. The limbs of the anterior and posterior divisions of the body of living horseshoe crabs differ in the loss of the outer and inner ramus, respectively, of an ancestral biramous limb. Here we report a new fossil horseshoe crab from the mid-Silurian Lagerstätte in Herefordshire, United Kingdom (approximately 425 Myr B.P.), a site that has yielded a remarkably preserved assemblage of soft-bodied fossils. The limbs of the new form can be homologized with those of living Limulus, but retain an ancestral biramous morphology. Remarkably, however, the two limb branches originate separately, providing fossil evidence to suggest that repression or loss of gene expression might have given rise to the appendage morphology of Limulus. Both branches of the prosomal limbs of this new fossil are robust and segmented in contrast to their morphology in Cambrian arthropods, revealing that a true biramous limb was once present in chelicerates as well as in the mandibulates.
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Affiliation(s)
- Derek E G Briggs
- Department of Geology and Geophysics, and Yale Peabody Museum of Natural History, Yale University, New Haven, CT 06520-8109, USA.
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31
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Sharma PP, Schwager EE, Extavour CG, Giribet G. Hox gene expression in the harvestman Phalangium opilio reveals divergent patterning of the chelicerate opisthosoma. Evol Dev 2012; 14:450-63. [DOI: 10.1111/j.1525-142x.2012.00565.x] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Affiliation(s)
| | - Evelyn E. Schwager
- Department of Organismic and Evolutionary Biology; Harvard University; 26 Oxford Street; Cambridge; MA; 02138; USA
| | - Cassandra G. Extavour
- Department of Organismic and Evolutionary Biology; Harvard University; 26 Oxford Street; Cambridge; MA; 02138; USA
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32
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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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Lehmann T, Hess M, Melzer RR. Wiring a periscope--ocelli, retinula axons, visual neuropils and the ancestrality of sea spiders. PLoS One 2012; 7:e30474. [PMID: 22279594 PMCID: PMC3261207 DOI: 10.1371/journal.pone.0030474] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2011] [Accepted: 12/19/2011] [Indexed: 11/19/2022] Open
Abstract
The Pycnogonida or sea spiders are cryptic, eight-legged arthropods with four median ocelli in a 'periscope' or eye tubercle. In older attempts at reconstructing phylogeny they were Arthropoda incertae sedis, but recent molecular trees placed them as the sister group either to all other euchelicerates or even to all euarthropods. Thus, pycnogonids are among the oldest extant arthropods and hold a key position for the understanding of arthropod evolution. This has stimulated studies of new sets of characters conductive to cladistic analyses, e.g. of the chelifores and of the hox gene expression pattern. In contrast knowledge of the architecture of the visual system is cursory. A few studies have analysed the ocelli and the uncommon "pseudoinverted" retinula cells. Moreover, analyses of visual neuropils are still at the stage of Hanström's early comprehensive works. We have therefore used various techniques to analyse the visual fibre pathways and the structure of their interrelated neuropils in several species. We found that pycnogonid ocelli are innervated to first and second visual neuropils in close vicinity to an unpaired midline neuropil, i.e. possibly the arcuate body, in a way very similar to ancestral euarthropods like Euperipatoides rowelli (Onychophora) and Limulus polyphemus (Xiphosura). This supports the ancestrality of pycnogonids and sheds light on what eyes in the pycnogonid ground plan might have 'looked' like. Recently it was suggested that arthropod eyes originated from simple ocelli similar to larval eyes. Hence, pycnogonid eyes would be one of the early offshoots among the wealth of more sophisticated arthropod eyes.
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34
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Morphogenesis of Pseudopallene sp. (Pycnogonida, Callipallenidae) I: embryonic development. Dev Genes Evol 2011; 221:309-28. [DOI: 10.1007/s00427-011-0382-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2011] [Accepted: 11/08/2011] [Indexed: 12/20/2022]
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Abstract
Arthropods are the most diverse group of animals and have been so since the Cambrian radiation. They belong to the protostome clade Ecdysozoa, with Onychophora (velvet worms) as their most likely sister group and tardigrades (water bears) the next closest relative. The arthropod tree of life can be interpreted as a five-taxon network, containing Pycnogonida, Euchelicerata, Myriapoda, Crustacea, and Hexapoda, the last two forming the clade Tetraconata or Pancrustacea. The unrooted relationship of Tetraconata to the three other lineages is well established, but of three possible rooting positions the Mandibulata hypothesis receives the most support. Novel approaches to studying anatomy with noninvasive three-dimensional reconstruction techniques, the application of these techniques to new and old fossils, and the so-called next-generation sequencing techniques are at the forefront of understanding arthropod relationships. Cambrian fossils assigned to the arthropod stem group inform on the origin of arthropod characters from a lobopodian ancestry. Monophyly of Pycnogonida, Euchelicerata, Myriapoda, Tetraconata, and Hexapoda is well supported, but the interrelationships of arachnid orders and the details of crustacean paraphyly with respect to Hexapoda remain the major unsolved phylogenetic problems.
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Affiliation(s)
- Gonzalo Giribet
- Museum of Comparative Zoology, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
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36
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37
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Steinmetz PRH, Kostyuchenko RP, Fischer A, Arendt D. The segmental pattern of otx, gbx, and Hox genes in the annelid Platynereis dumerilii. Evol Dev 2011; 13:72-9. [PMID: 21210944 DOI: 10.1111/j.1525-142x.2010.00457.x] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
SUMMARY Annelids and arthropods, despite their distinct classification as Lophotrochozoa and Ecdysozoa, present a morphologically similar, segmented body plan. To elucidate the evolution of segmentation and, ultimately, to align segments across remote phyla, we undertook a refined expression analysis to precisely register the expression of conserved regionalization genes with morphological boundaries and segmental units in the marine annelid Platynereis dumerilii. We find that Pdu-otx defines a brain region anterior to the first discernable segmental entity that is delineated by a stripe of engrailed-expressing cells. The first segment is a "cryptic" segment that lacks chaetae and parapodia. This and the subsequent three chaetigerous larval segments harbor the anterior expression boundary of gbx, hox1, hox4, and lox5 genes, respectively. This molecular segmental topography matches the segmental pattern of otx, gbx, and Hox gene expression in arthropods. Our data thus support the view that an ancestral ground pattern of segmental identities existed in the trunk of the last common protostome ancestor that was lost or modified in protostomes lacking overt segmentation.
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Affiliation(s)
- Patrick R H Steinmetz
- Developmental Biology Unit, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69012 Heidelberg, Germany.
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38
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Posnien N, Schinko JB, Kittelmann S, Bucher G. Genetics, development and composition of the insect head--a beetle's view. ARTHROPOD STRUCTURE & DEVELOPMENT 2010; 39:399-410. [PMID: 20800703 DOI: 10.1016/j.asd.2010.08.002] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/19/2010] [Revised: 08/08/2010] [Accepted: 08/15/2010] [Indexed: 05/29/2023]
Abstract
Many questions regarding evolution and ontogeny of the insect head remain open. Likewise, the genetic basis of insect head development is poorly understood. Recently, the investigation of gene expression data and the analysis of patterning gene function have revived interest in insect head development. Here, we argue that the red flour beetle Tribolium castaneum is a well suited model organism to spearhead research with respect to the genetic control of insect head development. We review recent molecular data and discuss its bearing on early development and morphogenesis of the head. We present a novel hypothesis on the ontogenetic origin of insect head sutures and review recent insights into the question on the origin of the labrum. Further, we argue that the study of developmental genes may identify the elusive anterior non-segmental region and present some evidence in favor of its existence. With respect to the question of evolution of patterning we show that the head Anlagen of the fruit fly Drosophila melanogaster and Tribolium differ considerably and we review profound differences of their genetic regulation. Finally, we discuss which insect model species might help us to answer the open questions concerning the genetic regulation of head development and its evolution.
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Affiliation(s)
- Nico Posnien
- Institute for Population Genetics, University of Veterinary Medicine Vienna, Veterinärplatz 1, Vienna, Austria
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39
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Masta SE, McCall A, Longhorn SJ. Rare genomic changes and mitochondrial sequences provide independent support for congruent relationships among the sea spiders (Arthropoda, Pycnogonida). Mol Phylogenet Evol 2010; 57:59-70. [DOI: 10.1016/j.ympev.2010.06.020] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2009] [Revised: 06/15/2010] [Accepted: 06/25/2010] [Indexed: 01/07/2023]
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40
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Mayer G, Whitington PM, Sunnucks P, Pflüger HJ. A revision of brain composition in Onychophora (velvet worms) suggests that the tritocerebrum evolved in arthropods. BMC Evol Biol 2010; 10:255. [PMID: 20727203 PMCID: PMC2933641 DOI: 10.1186/1471-2148-10-255] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2010] [Accepted: 08/21/2010] [Indexed: 01/15/2023] Open
Abstract
Background The composition of the arthropod head is one of the most contentious issues in animal evolution. In particular, controversy surrounds the homology and innervation of segmental cephalic appendages by the brain. Onychophora (velvet worms) play a crucial role in understanding the evolution of the arthropod brain, because they are close relatives of arthropods and have apparently changed little since the Early Cambrian. However, the segmental origins of their brain neuropils and the number of cephalic appendages innervated by the brain - key issues in clarifying brain composition in the last common ancestor of Onychophora and Arthropoda - remain unclear. Results Using immunolabelling and neuronal tracing techniques in the developing and adult onychophoran brain, we found that the major brain neuropils arise from only the anterior-most body segment, and that two pairs of segmental appendages are innervated by the brain. The region of the central nervous system corresponding to the arthropod tritocerebrum is not differentiated as part of the onychophoran brain but instead belongs to the ventral nerve cords. Conclusions Our results contradict the assumptions of a tripartite (three-segmented) brain in Onychophora and instead confirm the hypothesis of bipartite (two-segmented) brain composition. They suggest that the last common ancestor of Onychophora and Arthropoda possessed a brain consisting of protocerebrum and deutocerebrum whereas the tritocerebrum evolved in arthropods.
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Affiliation(s)
- Georg Mayer
- Institute of Biology II, Animal Evolution & Development, University of Leipzig, Talstrasse 33, D-04103 Leipzig, Germany.
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41
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Machner J, Scholtz G. A scanning electron microscopy study of the embryonic development of Pycnogonum litorale (Arthropoda, Pycnogonida). J Morphol 2010; 271:1306-18. [DOI: 10.1002/jmor.10871] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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42
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Meusemann K, von Reumont BM, Simon S, Roeding F, Strauss S, Kück P, Ebersberger I, Walzl M, Pass G, Breuers S, Achter V, von Haeseler A, Burmester T, Hadrys H, Wägele JW, Misof B. A phylogenomic approach to resolve the arthropod tree of life. Mol Biol Evol 2010; 27:2451-64. [PMID: 20534705 DOI: 10.1093/molbev/msq130] [Citation(s) in RCA: 264] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Arthropods were the first animals to conquer land and air. They encompass more than three quarters of all described living species. This extraordinary evolutionary success is based on an astoundingly wide array of highly adaptive body organizations. A lack of robustly resolved phylogenetic relationships, however, currently impedes the reliable reconstruction of the underlying evolutionary processes. Here, we show that phylogenomic data can substantially advance our understanding of arthropod evolution and resolve several conflicts among existing hypotheses. We assembled a data set of 233 taxa and 775 genes from which an optimally informative data set of 117 taxa and 129 genes was finally selected using new heuristics and compared with the unreduced data set. We included novel expressed sequence tag (EST) data for 11 species and all published phylogenomic data augmented by recently published EST data on taxonomically important arthropod taxa. This thorough sampling reduces the chance of obtaining spurious results due to stochastic effects of undersampling taxa and genes. Orthology prediction of genes, alignment masking tools, and selection of most informative genes due to a balanced taxa-gene ratio using new heuristics were established. Our optimized data set robustly resolves major arthropod relationships. We received strong support for a sister group relationship of onychophorans and euarthropods and strong support for a close association of tardigrades and cycloneuralia. Within pancrustaceans, our analyses yielded paraphyletic crustaceans and monophyletic hexapods and robustly resolved monophyletic endopterygote insects. However, our analyses also showed for few deep splits that were recently thought to be resolved, for example, the position of myriapods, a remarkable sensitivity to methods of analyses.
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Affiliation(s)
- Karen Meusemann
- Zoologisches Forschungsmuseum Alexander Koenig, Molecular Biology Unit, Bonn, Germany
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Studying sources of incongruence in arthropod molecular phylogenies: Sea spiders (Pycnogonida) as a case study. C R Biol 2010; 333:438-53. [DOI: 10.1016/j.crvi.2010.01.018] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2009] [Revised: 01/14/2010] [Accepted: 01/15/2010] [Indexed: 11/18/2022]
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Edgecombe GD. Arthropod phylogeny: an overview from the perspectives of morphology, molecular data and the fossil record. ARTHROPOD STRUCTURE & DEVELOPMENT 2010; 39:74-87. [PMID: 19854297 DOI: 10.1016/j.asd.2009.10.002] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2009] [Revised: 10/12/2009] [Accepted: 10/14/2009] [Indexed: 05/03/2023]
Abstract
Monophyly of Arthropoda is emphatically supported from both morphological and molecular perspectives. Recent work finds Onychophora rather than Tardigrada to be the closest relatives of arthropods. The status of tardigrades as panarthropods (rather than cycloneuralians) is contentious from the perspective of phylogenomic data. A grade of Cambrian taxa in the arthropod stem group includes gilled lobopodians, dinocaridids (e.g., anomalocaridids), fuxianhuiids and canadaspidids that inform on character acquisition between Onychophora and the arthropod crown group. A sister group relationship between Crustacea (itself likely paraphyletic) and Hexapoda is retrieved by diverse kinds of molecular data and is well supported by neuroanatomy. This clade, Tetraconata, can be dated to the early Cambrian by crown group-type mandibles. The rival Atelocerata hypothesis (Myriapoda+Hexapoda) has no molecular support. The basal node in the arthropod crown group is embroiled in a controversy over whether myriapods unite with chelicerates (Paradoxopoda or Myriochelata) or with crustaceans and hexapods (Mandibulata). Both groups find some molecular and morphological support, though Mandibulata is presently the stronger morphological hypothesis. Either hypothesis forces an unsampled ghost lineage for Myriapoda from the Cambrian to the mid Silurian.
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Affiliation(s)
- Gregory D Edgecombe
- Department of Palaeontology, Natural History Museum, Cromwell Road, London, UK.
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Hox Genes and the Body Plans of Chelicerates and Pycnogonids. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 689:125-32. [DOI: 10.1007/978-1-4419-6673-5_9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/11/2023]
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Liu Y, Maas A, Waloszek D. Early development of the anterior body region of the grey widow spider Latrodectus geometricus Koch, 1841 (Theridiidae, Araneae). ARTHROPOD STRUCTURE & DEVELOPMENT 2009; 38:401-16. [PMID: 19374954 DOI: 10.1016/j.asd.2009.04.001] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2008] [Revised: 03/26/2009] [Accepted: 04/01/2009] [Indexed: 05/14/2023]
Abstract
We document the early morphogenesis of Latrodectus geometricus, particularly of the anterior body region. Significant changes in the development of the external prosomal structures revealed with scanning electron microscopy (SEM) images include: (1) reorganisation of each pre-cheliceral lobe by subdivision and internalisation of its central area; (2) shortening of the ventro-median bridge connecting the pre-cheliceral lobes and its eventual disappearance; (3) appearance and expansion of a prospective mouth region between the pre-cheliceral lobes with a recessed median area surrounded by lip-like borders, the anterior lip-part developing into the hypostome; (4) reduction of the mouth region to an area around the hypostome and the lip-like latero-posterior border of the mouth opening; (5) change of the position of the mouth region from anterior to the insertions of the chelicerae to posterior to them; (6) eventual shortening of the mouth opening to a slit overhung by the hypostome; (7) origination of the prosomal shield from the anterior margin of the pre-cheliceral lobes and the tergal portions of the four posterior-most prosomal segments; and (8) expansion of a 'ventral sulcus' from the cheliceral to the fifth opisthosomal segment separating the sides of these segments. Embryonic features are compared across the Chelicerata and discussed briefly in a phylogenetic context.
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Affiliation(s)
- Yu Liu
- University of Ulm, Germany.
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Woods HA, Moran AL, Arango CP, Mullen L, Shields C. Oxygen hypothesis of polar gigantism not supported by performance of Antarctic pycnogonids in hypoxia. Proc Biol Sci 2009; 276:1069-75. [PMID: 19129117 PMCID: PMC2679066 DOI: 10.1098/rspb.2008.1489] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2008] [Accepted: 11/18/2008] [Indexed: 11/12/2022] Open
Abstract
Compared to temperate and tropical relatives, some high-latitude marine species are large-bodied, a phenomenon known as polar gigantism. A leading hypothesis on the physiological basis of gigantism posits that, in polar water, high oxygen availability coupled to low metabolic rates relieves constraints on oxygen transport and allows the evolution of large body size. Here, we test the oxygen hypothesis using Antarctic pycnogonids, which have been evolving in very cold conditions (-1.8-0 degrees C) for several million years and contain spectacular examples of gigantism. Pycnogonids from 12 species, spanning three orders of magnitude in body mass, were collected from McMurdo Sound, Antarctica. Individual sea spiders were forced into activity and their performance was measured at different experimental levels of dissolved oxygen (DO). The oxygen hypothesis predicts that, all else being equal, large pycnogonids should perform disproportionately poorly in hypoxia, an outcome that would appear as a statistically significant interaction between body size and oxygen level. In fact, although we found large effects of DO on performance, and substantial interspecific variability in oxygen sensitivity, there was no evidence for sizexDO interactions. These data do not support the oxygen hypothesis of Antarctic pycnogonid gigantism and suggest that explanations must be sought in other ecological or evolutionary processes.
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Affiliation(s)
- H Arthur Woods
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA.
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Kuhl G, Briggs DEG, Rust J. A Great-Appendage Arthropod with a Radial Mouth from the Lower Devonian Hunsruck Slate, Germany. Science 2009; 323:771-3. [DOI: 10.1126/science.1166586] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
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Brenneis G, Ungerer P, Scholtz G. The chelifores of sea spiders (Arthropoda, Pycnogonida) are the appendages of the deutocerebral segment. Evol Dev 2008; 10:717-24. [DOI: 10.1111/j.1525-142x.2008.00285.x] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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BARRETO FELIPES, AVISE JOHNC. Polygynandry and sexual size dimorphism in the sea spiderAmmothea hilgendorfi(Pycnogonida: Ammotheidae), a marine arthropod with brood-carrying males. Mol Ecol 2008; 17:4164-75. [DOI: 10.1111/j.1365-294x.2008.03895.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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