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Fritzsch B. Evolution and development of extraocular motor neurons, nerves and muscles in vertebrates. Ann Anat 2024; 253:152225. [PMID: 38346566 DOI: 10.1016/j.aanat.2024.152225] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2023] [Revised: 01/16/2024] [Accepted: 02/05/2024] [Indexed: 02/17/2024]
Abstract
The purpose of this review is to analyze the origin of ocular motor neurons, define the pattern of innervation of nerve fibers that project to the extraocular eye muscles (EOMs), describe congenital disorders that alter the development of ocular motor neurons, and provide an overview of vestibular pathway inputs to ocular motor nuclei. Six eye muscles are innervated by axons of three ocular motor neurons, the oculomotor (CNIII), trochlear (CNIV), and abducens (CNVI) neurons. Ocular motor neurons (CNIII) originate in the midbrain and innervate the ipsilateral orbit, except for the superior rectus and the levator palpebrae, which are contralaterally innervated. Trochlear motor neurons (CNIV) originate at the midbrain-hindbrain junction and innervate the contralateral superior oblique muscle. Abducens motor neurons (CNVI) originate variously in the hindbrain of rhombomeres r4-6 that innervate the posterior (or lateral) rectus muscle and innervate the retractor bulbi. Genes allow a distinction between special somatic (CNIII, IV) and somatic (CNVI) ocular motor neurons. Development of ocular motor neurons and their axonal projections to the EOMs may be derailed by various genetic causes, resulting in the congenital cranial dysinnervation disorders. The ocular motor neurons innervate EOMs while the vestibular nuclei connect with the midbrain-brainstem motor neurons.
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Affiliation(s)
- Bernd Fritzsch
- Department of Neurological Sciences, University of Nebraska Medical Center, NE, USA.
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Kong W, Cheng G, Cao J, Yu J, Wang X, Xu Z. Ocular mucosal homeostasis of teleost fish provides insight into the coevolution between microbiome and mucosal immunity. MICROBIOME 2024; 12:10. [PMID: 38218870 PMCID: PMC10787490 DOI: 10.1186/s40168-023-01716-6] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2023] [Accepted: 11/07/2023] [Indexed: 01/15/2024]
Abstract
BACKGROUND The visual organ plays a crucial role in sensing environmental information. However, its mucosal surfaces are constantly exposed to selective pressures from aquatic or airborne pathogens and microbial communities. Although few studies have characterized the conjunctival-associated lymphoid tissue (CALT) in the ocular mucosa (OM) of birds and mammals, little is known regarding the evolutionary origins and functions of immune defense and microbiota homeostasis of the OM in the early vertebrates. RESULTS Our study characterized the structure of the OM microbial ecosystem in rainbow trout (Oncorhynchus mykiss) and confirmed for the first time the presence of a diffuse mucosal-associated lymphoid tissue (MALT) in fish OM. Moreover, the microbial communities residing on the ocular mucosal surface contribute to shaping its immune environment. Interestingly, following IHNV infection, we observed robust immune responses, significant tissue damage, and microbial dysbiosis in the trout OM, particularly in the fornix conjunctiva (FC), which is characterized by the increase of pathobionts and a reduction of beneficial taxa in the relative abundance in OM. Critically, we identified a significant correlation between viral-induced immune responses and microbiome homeostasis in the OM, underscoring its key role in mucosal immunity and microbiota homeostasis. CONCLUSIONS Our findings suggest that immune defense and microbiota homeostasis in OM occurred concurrently in early vertebrate species, shedding light on the coevolution between microbiota and mucosal immunity. Video Abstract.
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Affiliation(s)
- Weiguang Kong
- Key Laboratory of Breeding Biotechnology and Sustainable Aquaculture, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China
| | - Gaofeng Cheng
- Department of Aquatic Animal Medicine, College of Fisheries, Huazhong Agricultural University, Wuhan, 430070, Hubei, China
| | - Jiafeng Cao
- Department of Aquatic Animal Medicine, College of Fisheries, Huazhong Agricultural University, Wuhan, 430070, Hubei, China
- Laboratory of Biochemistry and Molecular Biology, School of Marine Sciences, Meishan Campus, Ningbo University, Ningbo, 315832, China
| | - Jiaqian Yu
- Liaoning Key Laboratory of Marine Animal Immunology, Dalian Ocean University, Dalian, 116023, China
| | - Xinyou Wang
- Department of Aquatic Animal Medicine, College of Fisheries, Huazhong Agricultural University, Wuhan, 430070, Hubei, China
| | - Zhen Xu
- Key Laboratory of Breeding Biotechnology and Sustainable Aquaculture, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China.
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Fontes J, Castellano‐González G, Macena BCL, Afonso P. Hitchhiking to the abyss. Ecol Evol 2023; 13:e10126. [PMID: 37255846 PMCID: PMC10225908 DOI: 10.1002/ece3.10126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2023] [Revised: 04/21/2023] [Accepted: 05/09/2023] [Indexed: 06/01/2023] Open
Abstract
We investigated, for the first time, the hitchhiker-host fidelity of deep-diving whale sharks and Chilean devil rays. We found that two of the most ubiquitous oceanic hitchhikers, the common remora and the pilot fish, are able to follow their hosts to bathypelagic depths, where they are exposed to extreme gradients of light, dissolved oxygen, temperature, and pressure. We documented a deep dive of a large whale shark hosting remoras and pilot fish. Common remora was observed at the deepest section of the dive, at 1460 m, where the water temperature was 3.6°C. A pilot fish was recorded at 900 m, during the ascent phase, with the water temperature of 7.5°C. Although the adaptations that allow these hitchhikers to mitigate the impacts of such extreme environmental conditions remain unknown, we discuss these findings in the framework of the ecophysiology of deep diving and the hitchhiker-host fidelity.
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Affiliation(s)
- Jorge Fontes
- Ocean Sciences Institute – OkeanosUniversity of the AzoresHortaPortugal
| | | | - Bruno C. L. Macena
- Ocean Sciences Institute – OkeanosUniversity of the AzoresHortaPortugal
- Institute of Marine Research – IMARUniversity of the AzoresHortaPortugal
| | - Pedro Afonso
- Ocean Sciences Institute – OkeanosUniversity of the AzoresHortaPortugal
- Institute of Marine Research – IMARUniversity of the AzoresHortaPortugal
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Conserved subcortical processing in visuo-vestibular gaze control. Nat Commun 2022; 13:4699. [PMID: 35948549 PMCID: PMC9365791 DOI: 10.1038/s41467-022-32379-w] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Accepted: 07/27/2022] [Indexed: 11/24/2022] Open
Abstract
Gaze stabilization compensates for movements of the head or external environment to minimize image blurring. Multisensory information stabilizes the scene on the retina via the vestibulo-ocular (VOR) and optokinetic (OKR) reflexes. While the organization of neuronal circuits underlying VOR is well-described across vertebrates, less is known about the contribution and evolution of the OKR and the basic structures allowing visuo-vestibular integration. To analyze these neuronal pathways underlying visuo-vestibular integration, we developed a setup using a lamprey eye-brain-labyrinth preparation, which allowed coordinating electrophysiological recordings, vestibular stimulation with a moving platform, and visual stimulation via screens. Lampreys exhibit robust visuo-vestibular integration, with optokinetic information processed in the pretectum that can be downregulated from tectum. Visual and vestibular inputs are integrated at several subcortical levels. Additionally, saccades are present in the form of nystagmus. Thus, all basic components of the visuo-vestibular control of gaze were present already at the dawn of vertebrate evolution. Here, the authors show that gaze stabilization relies on a visuo-vestibular network conserved from lamprey to primates. This primordial blueprint highlights how visual and vestibular streams are organized to control fundamental aspects of eye movements.
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Braun CD, Arostegui MC, Thorrold SR, Papastamatiou YP, Gaube P, Fontes J, Afonso P. The Functional and Ecological Significance of Deep Diving by Large Marine Predators. ANNUAL REVIEW OF MARINE SCIENCE 2022; 14:129-159. [PMID: 34416123 DOI: 10.1146/annurev-marine-032521-103517] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Many large marine predators make excursions from surface waters to the deep ocean below 200 m. Moreover, the ability to access meso- and bathypelagic habitats has evolved independently across marine mammals, reptiles, birds, teleost fishes, and elasmobranchs. Theoretical and empirical evidence suggests a number of plausible functional hypotheses for deep-diving behavior. Developing ways to test among these hypotheses will, however, require new ways to quantify animal behavior and biophysical oceanographic processes at coherent spatiotemporal scales. Current knowledge gaps include quantifying ecological links between surface waters and mesopelagic habitats and the value of ecosystem services provided by biomass in the ocean twilight zone. Growing pressure for ocean twilight zone fisheries creates an urgent need to understand the importance of the deep pelagic ocean to large marine predators.
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Affiliation(s)
- Camrin D Braun
- Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA;
- School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington 98195, USA
| | - Martin C Arostegui
- Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA;
- Air-Sea Interaction and Remote Sensing Department, Applied Physics Laboratory, University of Washington, Seattle, Washington 98105, USA
| | - Simon R Thorrold
- Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA;
| | - Yannis P Papastamatiou
- Institute of Environment, Department of Biological Sciences, Florida International University, Miami, Florida 33181, USA
| | - Peter Gaube
- Air-Sea Interaction and Remote Sensing Department, Applied Physics Laboratory, University of Washington, Seattle, Washington 98105, USA
| | - Jorge Fontes
- Okeanos and Institute of Marine Research, University of the Azores, 9901-862 Horta, Portugal
| | - Pedro Afonso
- Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA;
- Okeanos and Institute of Marine Research, University of the Azores, 9901-862 Horta, Portugal
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Klimley AP. A Sensor Designed to Record Underwater Irradiance with Concern for a Shark's Spectral Sensitivity. BIOSENSORS 2021; 11:bios11040105. [PMID: 33916781 PMCID: PMC8065792 DOI: 10.3390/bios11040105] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Revised: 03/26/2021] [Accepted: 04/01/2021] [Indexed: 06/12/2023]
Abstract
To ascertain how scalloped hammerhead sharks make nightly migrations to their feeding grounds as many as 20 km from their daytime abode, a seamount, a sensor was developed that measured irradiance intensity within the spectral range and sensitivity of the vision of the species. Could the sharks guide their movements by sensing the polarity of irradiation energy radiated from the sun or moon that penetrated into the oceanic depths? Two sensory receptors, cones and rods, are present in the retina of sharks to enable them to see both during daytime and nighttime. The peak sensitivity of the cones is red-shifted due to the presence of these wavelengths during the former period, while their response is linear under the range of the high light levels also present at this time; the peak sensitivity of rods is blue-shifted due to the presence of these wavelengths during dawn, dusk, and nighttime and is linear over the complementary range of low light levels. Spectral response curves for these two receptors were determined for sharks, and an attempt was made to match those of the sensors to the shark's wavelength perception. The first sensor was matched to the photopic range using a photocell covered with a red-shifted gel filter; the second was matched to the scotopic range using a blue-shifted gel filter.
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Affiliation(s)
- A Peter Klimley
- College of Biological Sciences, University of California, Davis, CA 95616, USA
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Hernández-Núñez I, Robledo D, Mayeur H, Mazan S, Sánchez L, Adrio F, Barreiro-Iglesias A, Candal E. Loss of Active Neurogenesis in the Adult Shark Retina. Front Cell Dev Biol 2021; 9:628721. [PMID: 33644067 PMCID: PMC7905061 DOI: 10.3389/fcell.2021.628721] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2020] [Accepted: 01/12/2021] [Indexed: 01/09/2023] Open
Abstract
Neurogenesis is the process by which progenitor cells generate new neurons. As development progresses neurogenesis becomes restricted to discrete neurogenic niches, where it persists during postnatal life. The retina of teleost fishes is thought to proliferate and produce new cells throughout life. Whether this capacity may be an ancestral characteristic of gnathostome vertebrates is completely unknown. Cartilaginous fishes occupy a key phylogenetic position to infer ancestral states fixed prior to the gnathostome radiation. Previous work from our group revealed that the juvenile retina of the catshark Scyliorhinus canicula, a cartilaginous fish, shows active proliferation and neurogenesis. Here, we compared the morphology and proliferative status of the retina in catshark juveniles and adults. Histological and immunohistochemical analyses revealed an important reduction in the size of the peripheral retina (where progenitor cells are mainly located), a decrease in the thickness of the inner nuclear layer (INL), an increase in the thickness of the inner plexiform layer and a decrease in the cell density in the INL and in the ganglion cell layer in adults. Contrary to what has been reported in teleost fish, mitotic activity in the catshark retina was virtually absent after sexual maturation. Based on these results, we carried out RNA-Sequencing (RNA-Seq) analyses comparing the retinal transcriptome of juveniles and adults, which revealed a statistically significant decrease in the expression of many genes involved in cell proliferation and neurogenesis in adult catsharks. Our RNA-Seq data provides an excellent resource to identify new signaling pathways controlling neurogenesis in the vertebrate retina.
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Affiliation(s)
- Ismael Hernández-Núñez
- Departamento de Bioloxía Funcional, Facultade de Bioloxía, CIBUS, Universidade de Santiago de Compostela, Santiago de Compostela, Spain
| | - Diego Robledo
- The Roslin Institute and Royal (Dick) School of Veterinary Studies, University of Edinburgh, Edinburgh, United Kingdom
| | - Hélène Mayeur
- CNRS, Sorbonne Universités, UPMC Univ Paris 06, UMR7232, Observatoire Océanologique, Banyuls-sur-mer, France
| | - Sylvie Mazan
- CNRS, Sorbonne Universités, UPMC Univ Paris 06, UMR7232, Observatoire Océanologique, Banyuls-sur-mer, France
| | - Laura Sánchez
- Departamento de Zooloxía, Xenética e Antropoloxía Física, Facultade de Veterinaria, Universidade de Santiago de Compostela, Lugo, Spain
| | - Fátima Adrio
- Departamento de Bioloxía Funcional, Facultade de Bioloxía, CIBUS, Universidade de Santiago de Compostela, Santiago de Compostela, Spain
| | - Antón Barreiro-Iglesias
- Departamento de Bioloxía Funcional, Facultade de Bioloxía, CIBUS, Universidade de Santiago de Compostela, Santiago de Compostela, Spain
| | - Eva Candal
- Departamento de Bioloxía Funcional, Facultade de Bioloxía, CIBUS, Universidade de Santiago de Compostela, Santiago de Compostela, Spain
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8
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Collin SP, Collin HB. The Ultrastructure of the Nictitating Membrane of the Little Penguin ( Eudyptula minor, Aves). Integr Org Biol 2021; 2:obaa048. [PMID: 33791581 PMCID: PMC7810573 DOI: 10.1093/iob/obaa048] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The ultrastructure of the nictitating membrane in the little penguin Eudyptula minor was studied using both scanning and transmission electron microscopy to improve our understanding of the function of ocular adnexa in diving birds. Following euthanasia, eyes were enucleated and immersion fixed in Karnovsky's fixative. The nictitating membrane and conjunctiva were embedded in araldite and semi- or ultra-thin sections were stained and photographed using compound and transmission electron microscopes, respectively. Ultrastructural dimensions were measured directly from digital photographs. Surface ultrastructure was examined using scanning electron microscopy. The transparent nictitating membrane consists of a dense stroma surrounded by epithelia on both the external (conjunctival) and internal (bulbar) surfaces. The conjunctival surface of the membrane near the leading edge is covered by microvilli, which transition to microplicae and finally to microridges in the periphery. Beneath the epithelial cells, there is a well-developed basement membrane. Scattered throughout this epithelium are a few goblet cells. The surface of the bulbar epithelium is covered by microvilli near the leading edge, which become denser peripherally. The stroma consists of densely-packed collagen fibrils, which are randomly oriented in bundles near the leading edge but are aligned in the same direction parallel with the epithelial and corneal surfaces and with the leading edge, when the membrane is extended. The ultrastructure of the nictitating membrane in the little penguin differs from other birds and its function is predominantly protective, while preserving clear vision in both water and air.
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Affiliation(s)
- S P Collin
- School of Life Sciences, La Trobe University, Bundoora, VIC 3086, Australia.,Oceans Graduate School and the Oceans Institute, The University of Western Australia, Crawley, WA 6009, Australia
| | - H B Collin
- Department of Optometry and Vision Science, University of New South Wales, Kensington, NSW 2052, Australia
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Carleton KL, Escobar-Camacho D, Stieb SM, Cortesi F, Marshall NJ. Seeing the rainbow: mechanisms underlying spectral sensitivity in teleost fishes. J Exp Biol 2020; 223:jeb193334. [PMID: 32327561 PMCID: PMC7188444 DOI: 10.1242/jeb.193334] [Citation(s) in RCA: 51] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Among vertebrates, teleost eye diversity exceeds that found in all other groups. Their spectral sensitivities range from ultraviolet to red, and the number of visual pigments varies from 1 to over 40. This variation is correlated with the different ecologies and life histories of fish species, including their variable aquatic habitats: murky lakes, clear oceans, deep seas and turbulent rivers. These ecotopes often change with the season, but fish may also migrate between ecotopes diurnally, seasonally or ontogenetically. To survive in these variable light habitats, fish visual systems have evolved a suite of mechanisms that modulate spectral sensitivities on a range of timescales. These mechanisms include: (1) optical media that filter light, (2) variations in photoreceptor type and size to vary absorbance and sensitivity, and (3) changes in photoreceptor visual pigments to optimize peak sensitivity. The visual pigment changes can result from changes in chromophore or changes to the opsin. Opsin variation results from changes in opsin sequence, opsin expression or co-expression, and opsin gene duplications and losses. Here, we review visual diversity in a number of teleost groups where the structural and molecular mechanisms underlying their spectral sensitivities have been relatively well determined. Although we document considerable variability, this alone does not imply functional difference per se. We therefore highlight the need for more studies that examine species with known sensitivity differences, emphasizing behavioral experiments to test whether such differences actually matter in the execution of visual tasks that are relevant to the fish.
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Affiliation(s)
- Karen L Carleton
- Department of Biology, University of Maryland, College Park, MD 20742, USA
| | | | - Sara M Stieb
- Centre of Ecology, Evolution and Biogeochemistry, EAWAG Swiss Federal Institute of Aquatic Science and Technology, 6047 Kastanienbaum, Switzerland
- Institute of Ecology and Evolution, University of Bern, 3012 Bern, Switzerland
- Queensland Brain Institute, University of Queensland, Brisbane 4072 QLD, Australia
| | - Fabio Cortesi
- Queensland Brain Institute, University of Queensland, Brisbane 4072 QLD, Australia
| | - N Justin Marshall
- Queensland Brain Institute, University of Queensland, Brisbane 4072 QLD, Australia
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Vision in sharks and rays: Opsin diversity and colour vision. Semin Cell Dev Biol 2020; 106:12-19. [PMID: 32331993 DOI: 10.1016/j.semcdb.2020.03.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Revised: 03/31/2020] [Accepted: 03/31/2020] [Indexed: 01/11/2023]
Abstract
The visual sense of elasmobranch fishes is poorly studied compared to their bony cousins, the teleosts. Nevertheless, the elasmobranch eye features numerous specialisations that have no doubt facilitated the diversification and evolutionary success of this fascinating taxon. In this review, I highlight recent discoveries on the nature and phylogenetic distribution of visual pigments in sharks and rays. Whereas most rays appear to be cone dichromats, all sharks studied to date are cone monochromats and, as a group, have likely abandoned colour vision on multiple occasions. This situation in sharks mirrors that seen in other large marine predators, the pinnipeds and cetaceans, which leads us to reassess the costs and benefits of multiple cone pigments and wavelength discrimination in the marine environment.
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Peel LR, Collin SP, Hart NS. Retinal topography and spectral sensitivity of the Port Jackson shark (
Heterodontus portusjacksoni
). J Comp Neurol 2020; 528:2831-2847. [DOI: 10.1002/cne.24911] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Revised: 03/20/2020] [Accepted: 03/20/2020] [Indexed: 12/14/2022]
Affiliation(s)
- Lauren R. Peel
- School of Biological Sciences University of Western Australia Crawley Western Australia Australia
- The Oceans Institute University of Western Australia Crawley Western Australia Australia
- The Oceans Graduate School University of Western Australia Crawley Western Australia Australia
| | - Shaun P. Collin
- School of Biological Sciences University of Western Australia Crawley Western Australia Australia
- The Oceans Institute University of Western Australia Crawley Western Australia Australia
- The Oceans Graduate School University of Western Australia Crawley Western Australia Australia
- School of Life Sciences, La Trobe University Bundoora Victoria Australia
| | - Nathan S. Hart
- School of Biological Sciences University of Western Australia Crawley Western Australia Australia
- Department of Biological Sciences Macquarie University Sydney New South Wales Australia
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Kelly M, Collin S, Hemmi J, Lesku J. Evidence for Sleep in Sharks and Rays: Behavioural, Physiological, and Evolutionary Considerations. BRAIN, BEHAVIOR AND EVOLUTION 2019; 94:37-50. [DOI: 10.1159/000504123] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Accepted: 10/14/2019] [Indexed: 11/19/2022]
Abstract
Sleep is widespread across the animal kingdom. However, most comparative sleep data exist for terrestrial vertebrates, with much less known about sleep in amphibians, bony fishes, and invertebrates. There is an absence of knowledge on sleep in cartilaginous fishes. Sharks and rays are amongst the earliest vertebrates, and may hold clues to the evolutionary history of sleep and sleep states found in more derived animals, such as mammals and birds. Here, we review the literature concerning activity patterns, sleep behaviour, and electrophysiological evidence for sleep in cartilaginous (and bony) fishes following an exhaustive literature search that found more than 80 relevant studies in laboratory and field environments. Evidence for sleep in sharks and rays that respire without swimming is preliminary; evidence for sleep in continuously swimming fishes is currently absent. We discuss ways in which the latter group might sleep concurrent with sustained movement, and conclude with suggestions for future studies in order to provide more comprehensive data on when, how, and why sharks and rays sleep.
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