1
|
Chappell DR, Speiser DI. Polarization sensitivity and decentralized visual processing in an animal with a distributed visual system. J Exp Biol 2023; 226:286798. [PMID: 36714995 DOI: 10.1242/jeb.244710] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2022] [Accepted: 01/19/2023] [Indexed: 01/31/2023]
Abstract
The marine mollusc Acanthopleura granulata (Mollusca; Polyplacophora) has a distributed visual array composed of hundreds of small image-forming eyes embedded within its eight dorsal shell plates. As in other animals with distributed visual systems, we still have a poor understanding of the visual capabilities of A. granulata and we have yet to learn where and how it processes visual information. Using behavioral trials involving isoluminant looming visual stimuli, we found that A. granulata demonstrates spatial vision with an angular resolution of 6 deg. We also found that A. granulata responds to looming stimuli defined by contrasting angles of linear polarization. To learn where and how A. granulata processes visual information, we traced optic nerves using fluorescent lipophilic dyes. We found that the optic nerves innervate the underlying lateral neuropil, a neural tissue layer that circumnavigates the body. Adjacent optic nerves innervate the lateral neuropil with highly overlapping arborizations, suggesting it is the site of an integrated visuotopic map. Using immunohistochemistry, we found that the lateral neuropil of A. granulata is subdivided into two separate layers. In comparison, we found that a chiton with eyespots (Chiton tuberculatus) and two eyeless chitons (Ischnochiton papillosus and Chaetopleura apiculata) have lateral neuropil that is a singular circular layer without subdivision, findings consistent with previous work on chiton neuroanatomy. Overall, our results suggest that A. granulata effectuates its visually mediated behaviors using a unique processing scheme: it extracts spatial and polarization information using a distributed visual system, and then integrates and processes that information using decentralized neural circuits.
Collapse
Affiliation(s)
- Daniel R Chappell
- Department of Biological Sciences, University of South Carolina, 715 Sumter Street, Columbia, SC 29208, USA
| | - Daniel I Speiser
- Department of Biological Sciences, University of South Carolina, 715 Sumter Street, Columbia, SC 29208, USA
| |
Collapse
|
2
|
Smith AM, Peebles BA, Spencer HG. Directly observed images through the shell-lenses of Onithochiton neglectus (Mollusca: Polyplacophora: Chitonidae). MOLLUSCAN RESEARCH 2022. [DOI: 10.1080/13235818.2022.2144089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Affiliation(s)
- Abigail M. Smith
- Department of Marine Science, University of Otago, Dunedin, New Zealand
| | - Bryce A. Peebles
- Department of Marine Science, University of Otago, Dunedin, New Zealand
| | | |
Collapse
|
3
|
Chappell DR, Horan TM, Speiser DI. Panoramic spatial vision in the bay scallop Argopecten irradians. Proc Biol Sci 2021; 288:20211730. [PMID: 34753355 PMCID: PMC8580434 DOI: 10.1098/rspb.2021.1730] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2021] [Accepted: 10/20/2021] [Indexed: 11/12/2022] Open
Abstract
We have a growing understanding of the light-sensing organs and light-influenced behaviours of animals with distributed visual systems, but we have yet to learn how these animals convert visual input into behavioural output. It has been suggested they consolidate visual information early in their sensory-motor pathways, resulting in them being able to detect visual cues (spatial resolution) without being able to locate them (spatial vision). To explore how an animal with dozens of eyes processes visual information, we analysed the responses of the bay scallop Argopecten irradians to both static and rotating visual stimuli. We found A. irradians distinguish between static visual stimuli in different locations by directing their sensory tentacles towards them and were more likely to point their extended tentacles towards larger visual stimuli. We also found that scallops track rotating stimuli with individual tentacles and with rotating waves of tentacle extension. Our results show, to our knowledge for the first time that scallops have both spatial resolution and spatial vision, indicating their sensory-motor circuits include neural representations of their visual surroundings. Exploring a wide range of animals with distributed visual systems will help us learn the different ways non-cephalized animals convert sensory input into behavioural output.
Collapse
Affiliation(s)
- Daniel R. Chappell
- Department of Biological Sciences, University of South Carolina, 715 Sumter Street, Columbia, SC 29208, USA
| | - Tyler M. Horan
- Department of Biological Sciences, University of South Carolina, 715 Sumter Street, Columbia, SC 29208, USA
| | - Daniel I. Speiser
- Department of Biological Sciences, University of South Carolina, 715 Sumter Street, Columbia, SC 29208, USA
| |
Collapse
|
4
|
Deryckere A, Styfhals R, Elagoz AM, Maes GE, Seuntjens E. Identification of neural progenitor cells and their progeny reveals long distance migration in the developing octopus brain. eLife 2021; 10:e69161. [PMID: 34425939 PMCID: PMC8384421 DOI: 10.7554/elife.69161] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2021] [Accepted: 07/21/2021] [Indexed: 12/28/2022] Open
Abstract
Cephalopods have evolved nervous systems that parallel the complexity of mammalian brains in terms of neuronal numbers and richness in behavioral output. How the cephalopod brain develops has only been described at the morphological level, and it remains unclear where the progenitor cells are located and what molecular factors drive neurogenesis. Using histological techniques, we located dividing cells, neural progenitors and postmitotic neurons in Octopus vulgaris embryos. Our results indicate that an important pool of progenitors, expressing the conserved bHLH transcription factors achaete-scute or neurogenin, is located outside the central brain cords in the lateral lips adjacent to the eyes, suggesting that newly formed neurons migrate into the cords. Lineage-tracing experiments then showed that progenitors, depending on their location in the lateral lips, generate neurons for the different lobes, similar to the squid Doryteuthis pealeii. The finding that octopus newborn neurons migrate over long distances is reminiscent of vertebrate neurogenesis and suggests it might be a fundamental strategy for large brain development.
Collapse
Affiliation(s)
- Astrid Deryckere
- Laboratory of Developmental Neurobiology, Department of Biology, KU LeuvenLeuvenBelgium
| | - Ruth Styfhals
- Laboratory of Developmental Neurobiology, Department of Biology, KU LeuvenLeuvenBelgium
- Department of Biology and Evolution of Marine Organisms, Stazione Zoologica Anton DohrnNaplesItaly
| | - Ali Murat Elagoz
- Laboratory of Developmental Neurobiology, Department of Biology, KU LeuvenLeuvenBelgium
| | - Gregory E Maes
- Center for Human Genetics, Genomics Core, UZ-KU LeuvenLeuvenBelgium
- Centre for Sustainable Tropical Fisheries and Aquaculture, College of Science and Engineering, James Cook UniversityTownsvilleAustralia
- Laboratory of Biodiversity and Evolutionary Genomics, Department of Biology, KU LeuvenLeuvenBelgium
| | - Eve Seuntjens
- Laboratory of Developmental Neurobiology, Department of Biology, KU LeuvenLeuvenBelgium
| |
Collapse
|
5
|
Sigwart JD, Sumner-Rooney L. Continuous and Regular Expansion of a Distributed Visual System in the Eyed Chiton Tonicia lebruni. THE BIOLOGICAL BULLETIN 2021; 240:23-33. [PMID: 33730533 DOI: 10.1086/712114] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
AbstractChitons have a distinctive armature of eight articulating dorsal shells. In all living species, the shell valves are covered by a dense array of sensory pores called aesthetes; but in some taxa, a subset of these are elaborated into lensed eyes, which are capable of spatial vision. We collected a complete ontogenetic series of the eyed chiton Tonicia lebruni de Rochebrune, 1884 to examine the growth of this visual network and found that it expands continuously as eyes are added at the margin during shell growth. Our dataset ranged from a 2.58-mm juvenile with only 16 eyes to adults of 25-31 mm with up to 557 eyes each. This allowed us to investigate the organization (and potential constraints therein) of these sensory structures and their development. Chiton eyes are constrained to a narrowly defined region of the shell, and data from T. lebruni indicate that they are arranged roughly bilaterally symmetrically. We found deviations from symmetry of up to 10%, similar to irregularity reported in some other animals with multiplied eyes. Distances separating successive eyes indicate that, while shell growth slows during the life of an individual chiton, eyes are generated at regular time intervals. Although we could not identify a specific eye-producing tissue or organ, we propose that the generation of new eyes is controlled by a clock-like mechanism with a stable periodicity. The apparent regularity and organization of the chiton visual system are far greater than previously appreciated. This does not imply the integration of shell eyes to form composite images, but symmetry and regular organization could be equally beneficial to a highly duplicated system by ensuring even and comprehensive sampling of the total field of view.
Collapse
|
6
|
Visual Ecology: Now You See, Now You Don't. Curr Biol 2020; 30:R71-R73. [PMID: 31962079 DOI: 10.1016/j.cub.2019.12.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
During the day, the brittle star Ophiocoma wendtii demonstrates spatial vision due to a distributed network of extraocular photoreceptors whose fields of view are restricted by chromatophores. At night, these chromatophores contract and O. wendtii loses spatial vision.
Collapse
|
7
|
New data from Monoplacophora and a carefully-curated dataset resolve molluscan relationships. Sci Rep 2020; 10:101. [PMID: 31919367 PMCID: PMC6952402 DOI: 10.1038/s41598-019-56728-w] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2019] [Accepted: 12/12/2019] [Indexed: 01/14/2023] Open
Abstract
Relationships among the major lineages of Mollusca have long been debated. Morphological studies have considered the rarely collected Monoplacophora (Tryblidia) to have several plesiomorphic molluscan traits. The phylogenetic position of this group is contentious as morphologists have generally placed this clade as the sister taxon of the rest of Conchifera whereas earlier molecular studies supported a clade of Monoplacophora + Polyplacophora (Serialia) and phylogenomic studies have generally recovered a clade of Monoplacophora + Cephalopoda. Phylogenomic studies have also strongly supported a clade including Gastropoda, Bivalvia, and Scaphopoda, but relationships among these taxa have been inconsistent. In order to resolve conchiferan relationships and improve understanding of early molluscan evolution, we carefully curated a high-quality data matrix and conducted phylogenomic analyses with broad taxon sampling including newly sequenced genomic data from the monoplacophoran Laevipilina antarctica. Whereas a partitioned maximum likelihood (ML) analysis using site-homogeneous models recovered Monoplacophora sister to Cephalopoda with moderate support, both ML and Bayesian inference (BI) analyses using mixture models recovered Monoplacophora sister to all other conchiferans with strong support. A supertree approach also recovered Monoplacophora as the sister taxon of a clade composed of the rest of Conchifera. Gastropoda was recovered as the sister taxon of Scaphopoda in most analyses, which was strongly supported when mixture models were used. A molecular clock based on our BI topology dates diversification of Mollusca to ~546 MYA (+/- 6 MYA) and Conchifera to ~540 MYA (+/- 9 MYA), generally consistent with previous work employing nuclear housekeeping genes. These results provide important resolution of conchiferan mollusc phylogeny and offer new insights into ancestral character states of major mollusc clades.
Collapse
|
8
|
Abstract
Many animals with external armour, such as hedgehogs, isopods and trilobites, curl into a protective ball when disturbed. However, in situations where predators would engulf an exposed animal whole, regardless of position, conglobation may provide limited added defence and the benefits were previously unclear. We show that polyplacophoran molluscs (chitons) are three times less likely to spend time curled into a ball in the presence of a predator. When the cue of a potential predator is present, animals instead spend significantly more time in active, high risk, high reward behaviours such as arching, balancing on the head and tail ends of their girdle and pushing the soft foot up into an exposed position. Arching increases vulnerability, but also can increase the likelihood of rapidly encountering new substratum that would allow the animal to right itself. In some other animals, the ability to roll into a ball is associated with rolling away from danger. Curling into a ball would improve mobility, to be rolled on to a safer position, but reattachment is the higher priority for chitons in the face of danger.
Collapse
Affiliation(s)
- Julia D Sigwart
- Marine Laboratory, Queen's University Belfast, 12-13 The Strand, Portaferry, Northern Ireland BT22 1PF, UK
| | - Geerat J Vermeij
- Department of Earth and Planetary Science, University of California, Davis, CA 95616, USA
| | - Peter Hoyer
- Marine Laboratory, Queen's University Belfast, 12-13 The Strand, Portaferry, Northern Ireland BT22 1PF, UK
| |
Collapse
|
9
|
Parry L, Caron JB. Canadia spinosa and the early evolution of the annelid nervous system. SCIENCE ADVANCES 2019; 5:eaax5858. [PMID: 31535028 PMCID: PMC6739095 DOI: 10.1126/sciadv.aax5858] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Accepted: 08/09/2019] [Indexed: 05/19/2023]
Abstract
Annelid worms are a disparate, primitively segmented clade of bilaterians that first appear during the early Cambrian Period. Reconstructing their early evolution is complicated by the extreme morphological diversity in early diverging lineages, rapid diversification, and sparse fossil record. Canadia spinosa, a Burgess Shale fossil polychaete, is redescribed as having palps with feeding grooves, a dorsal median antenna and biramous parapodia associated with the head and flanking a ventral mouth. Carbonaceously preserved features are identified as a terminal brain, circumoral connectives, a midventral ganglionated nerve cord and prominent parapodial nerves. Phylogenetic analysis recovers neuroanatomically simple extant taxa as the sister group of other annelids, but the phylogenetic position of Canadia suggests that the annelid ancestor was reasonably complex neuroanatomically and that reduction of the nervous system occurred several times independently in the subsequent 500 million years of annelid evolution.
Collapse
Affiliation(s)
- Luke Parry
- Department of Natural History, Palaeobiology, Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario M5S 2C6, Canada
- Department of Geology and Geophysics, Yale University, New Haven, CT 06511, USA
- Corresponding author.
| | - Jean-Bernard Caron
- Department of Geology and Geophysics, Yale University, New Haven, CT 06511, USA
- Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario M5S 3B2, Canada
- Department of Earth Sciences, University of Toronto, Toronto, Ontario M5S 3B1, Canada
| |
Collapse
|
10
|
De Oliveira AL, Calcino A, Wanninger A. Extensive conservation of the proneuropeptide and peptide prohormone complement in mollusks. Sci Rep 2019; 9:4846. [PMID: 30890731 PMCID: PMC6425005 DOI: 10.1038/s41598-019-40949-0] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2018] [Accepted: 02/25/2019] [Indexed: 12/27/2022] Open
Abstract
As one of the most diverse groups of invertebrate animals, mollusks represent powerful models for neurobiological and developmental studies. Neuropeptides and peptide hormones are a heterogeneous class of signalling molecules involved in chemical communication between neurons and in neuroendocrine regulation. Here we present a fine-grained view of the molluscan neuropeptide and peptide hormone toolkit. Our results expand the distribution of several peptide families (e.g., prokineticin, insulin-related peptides, prohormone-4, LFRFamide) within Lophotrochozoa and provide evidence for an early origin of others (e.g., GNXQN/prohormone-2, neuroparsin). We identified a new peptide family broadly distributed among conchiferan mollusks, the PXRX family. We found the Wnt antagonist dickkopf1/2/4 ortholog in lophotrochozoans and nematodes and reveal that the egg-laying hormone family is a DH44 homolog restricted to gastropods. Our data demonstrate that numerous peptides evolved much earlier than previously assumed and that key signalling elements are extensively conserved among extant mollusks.
Collapse
Affiliation(s)
- A L De Oliveira
- Department of Integrative Zoology, Faculty of Life Sciences, University of Vienna, Althanstraße 14, Vienna, 1090, Austria
| | - A Calcino
- Department of Integrative Zoology, Faculty of Life Sciences, University of Vienna, Althanstraße 14, Vienna, 1090, Austria
| | - A Wanninger
- Department of Integrative Zoology, Faculty of Life Sciences, University of Vienna, Althanstraße 14, Vienna, 1090, Austria.
| |
Collapse
|
11
|
Beckers P, Helm C, Purschke G, Worsaae K, Hutchings P, Bartolomaeus T. The central nervous system of Oweniidae (Annelida) and its implications for the structure of the ancestral annelid brain. Front Zool 2019; 16:6. [PMID: 30911320 PMCID: PMC6417257 DOI: 10.1186/s12983-019-0305-1] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2018] [Accepted: 02/26/2019] [Indexed: 11/29/2022] Open
Abstract
Background Recent phylogenomic analyses congruently reveal a basal clade which consists of Oweniidae and Mageloniidae as sister group to the remaining Annelida. These results indicate that the last common ancestor of Annelida was a tube-dwelling organism. They also challenge traditional evolutionary hypotheses of different organ systems, among them the nervous system. In textbooks the central nervous system is described as consisting of a ganglionic ventral nervous system and a dorsally located brain with different tracts that connect certain parts of the brain to each other. Only limited information on the fine structure, however, is available for Oweniidae, which constitute the sister group (possibly together with Magelonidae) to all remaining annelids. Results The brain of Oweniidae is ring- shaped and basiepidermal. Ganglia, higher brain centers or complex sensory organs do not exist; instead the central nervous system is medullary. Posterior to the brain the ventral medullary cord arises directly from the ventral region of the brain in Myriowenia sp. while in Owenia fusiformis two medullary cords arise perpendicular to the brain ring, extend caudally and fuse posterior. The central nervous system is composed of a central neuropil and surrounding somata of the neurons. According to ultrastructural and histological data only one type of neuron is present in the central nervous system. Conclusion The central nervous system of Oweniidae is the simplest in terms of enlargement of the dorsal part of the brain and neuron distribution found among Annelida. Our investigation suggests that neither ganglia nor commissures inside the brain neuropil or clusters of polymorphic neurons were present in the annelid stem species. These structures evolved later within Annelida, most likely in the stem lineage of Amphinomidae, Sipuncula and Pleistoannelida. Palps were supposedly present in the last common ancestor of annelids and innervated by two nerves originating in the dorsal part of the brain. A broader comparison with species of each major spiralian clade shows the medullary nervous system to be a common feature and thus possibly representing the ancestral state of the spiralian nervous system. Moreover, ganglia and clusters of polymorphic neurons seemingly evolved independently in the compared taxa of Spiralia and Annelida. Electronic supplementary material The online version of this article (10.1186/s12983-019-0305-1) contains supplementary material, which is available to authorized users.
Collapse
Affiliation(s)
- Patrick Beckers
- 1Institute of Evolutionary Biology, University of Bonn, 53121 Bonn, Germany
| | - Conrad Helm
- 2Johann-Friedrich-Blumenbach Institute for Zoology & Anthropology Animal Evolution and Biodiversity, University of Göttingen, 37073 Göttingen, Germany
| | - Günter Purschke
- 3Department of Developmental Biology and Zoology, University of Osnabrück, 49069 Osnabrück, Germany
| | - Katrine Worsaae
- 4Department of Biology, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Pat Hutchings
- 5Australian Museum Research Institute, Australian Museum, Sydney, NSW 2010 Australia.,6Department of Biological Sciences, Macquarie University, North Ryde, 2109 Australia
| | | |
Collapse
|
12
|
Kingston ACN, Chappell DR, Speiser DI. Evidence for spatial vision in Chiton tuberculatus, a chiton with eyespots. ACTA ACUST UNITED AC 2018; 221:jeb.183632. [PMID: 30127078 DOI: 10.1242/jeb.183632] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Accepted: 08/07/2018] [Indexed: 11/20/2022]
Abstract
To better understand relationships between the structures and functions of the distributed visual systems of chitons, we compare how morphological differences between the light-sensing structures of these animals relate to their visually guided behaviors. All chitons have sensory organs - termed aesthetes - embedded within their protective shell plates. In some species, the aesthetes are interspersed with small, image-forming eyes. In other species, the aesthetes are paired with pigmented eyespots. Previously, we compared the visually influenced behaviors of chitons with aesthetes to those of chitons with both aesthetes and eyes. Here, we characterize the visually influenced behaviors of chitons with aesthetes and eyespots. We find that chitons with eyespots engage in behaviors consistent with spatial vision, but appear to use spatial vision for different tasks than chitons with eyes. Unlike chitons with eyes, Chiton tuberculatus and C. marmoratus fail to distinguish between sudden appearances of overhead objects and equivalent, uniform changes in light levels. We also find that C. tuberculatus orients to static objects with angular sizes as small as 10 deg. Thus, C. tuberculatus demonstrates spatial resolution that is at least as fine as that demonstrated by chitons with eyes. The eyespots of Chiton are smaller and more numerous than the eyes found in other chitons and they are separated by angles of <0.5 deg, suggesting that the light-influenced behaviors of Chiton may be more accurately predicted by the network properties of their distributed visual system than by the structural properties of their individual light-detecting organs.
Collapse
Affiliation(s)
- Alexandra C N Kingston
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
| | - Daniel R Chappell
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
| | - Daniel I Speiser
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
| |
Collapse
|
13
|
Helm C, Beckers P, Bartolomaeus T, Drukewitz SH, Kourtesis I, Weigert A, Purschke G, Worsaae K, Struck TH, Bleidorn C. Convergent evolution of the ladder-like ventral nerve cord in Annelida. Front Zool 2018; 15:36. [PMID: 30275868 PMCID: PMC6161469 DOI: 10.1186/s12983-018-0280-y] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Accepted: 09/04/2018] [Indexed: 12/15/2022] Open
Abstract
BACKGROUND A median, segmented, annelid nerve cord has repeatedly been compared to the arthropod and vertebrate nerve cords and became the most used textbook representation of the annelid nervous system. Recent phylogenomic analyses, however, challenge the hypothesis that a subepidermal rope-ladder-like ventral nerve cord (VNC) composed of a paired serial chain of ganglia and somata-free connectives represents either a plesiomorphic or a typical condition in annelids. RESULTS Using a comparative approach by combining phylogenomic analyses with morphological methods (immunohistochemistry and CLSM, histology and TEM), we compiled a comprehensive dataset to reconstruct the evolution of the annelid VNC. Our phylogenomic analyses generally support previous topologies. However, the so far hard-to-place Apistobranchidae and Psammodrilidae are now incorporated among the basally branching annelids with high support. Based on this topology we reconstruct an intraepidermal VNC as the ancestral state in Annelida. Thus, a subepidermal ladder-like nerve cord clearly represents a derived condition. CONCLUSIONS Based on the presented data, a ladder-like appearance of the ventral nerve cord evolved repeatedly, and independently of the transition from an intraepidermal to a subepidermal cord during annelid evolution. Our investigations thereby propose an alternative set of neuroanatomical characteristics for the last common ancestor of Annelida or perhaps even Spiralia.
Collapse
Affiliation(s)
- Conrad Helm
- Animal Evolution and Biodiversity, Georg-August-University Göttingen, 37073 Göttingen, Germany
| | - Patrick Beckers
- Institute of Evolutionary Biology and Ecology, University of Bonn, 53121 Bonn, Germany
| | - Thomas Bartolomaeus
- Institute of Evolutionary Biology and Ecology, University of Bonn, 53121 Bonn, Germany
| | | | - Ioannis Kourtesis
- Animal Evolution and Biodiversity, Georg-August-University Göttingen, 37073 Göttingen, Germany
| | - Anne Weigert
- Department of Evolutionary Genetics, Max Planck Institute for Evolutionary Anthropology, 04103 Leipzig, Germany
| | - Günter Purschke
- Department of Developmental Biology and Zoology, University of Osnabrück, 49069 Osnabrück, Germany
| | - Katrine Worsaae
- Department of Biology, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Torsten H. Struck
- Frontiers in Evolutionary Zoology, Natural History Museum, University of Oslo, P.O. Box 1172, Blindern, NO-0318 Oslo, Norway
| | - Christoph Bleidorn
- Animal Evolution and Biodiversity, Georg-August-University Göttingen, 37073 Göttingen, Germany
- German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Deutscher Platz 5e, 04103 Leipzig, Germany
| |
Collapse
|