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Mitra AT, Womack MC, Gower DJ, Streicher JW, Clark B, Bell RC, Schott RK, Fujita MK, Thomas KN. Ocular lens morphology is influenced by ecology and metamorphosis in frogs and toads. Proc Biol Sci 2022; 289:20220767. [PMID: 36382525 PMCID: PMC9667364 DOI: 10.1098/rspb.2022.0767] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The shape and relative size of an ocular lens affect the focal length of the eye, with consequences for visual acuity and sensitivity. Lenses are typically spherical in aquatic animals with camera-type eyes and axially flattened in terrestrial species to facilitate vision in optical media with different refractive indices. Frogs and toads (Amphibia: Anura) are ecologically diverse, with many species shifting from aquatic to terrestrial ecologies during metamorphosis. We quantified lens shape and relative size using 179 micro X-ray computed tomography scans of 126 biphasic anuran species and tested for correlations with life stage, environmental transitions, adult habits and adult activity patterns. Across broad phylogenetic diversity, tadpole lenses are more spherical than those of adults. Biphasic species with aquatic larvae and terrestrial adults typically undergo ontogenetic changes in lens shape, whereas species that remain aquatic as adults tend to retain more spherical lenses after metamorphosis. Further, adult lens shape is influenced by adult habit; notably, fossorial adults tend to retain spherical lenses following metamorphosis. Finally, lens size relative to eye size is smaller in aquatic and semiaquatic species than other adult ecologies. Our study demonstrates how ecology shapes visual systems, and the power of non-invasive imaging of museum specimens for studying sensory evolution.
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Affiliation(s)
- Amartya T. Mitra
- Division of Biosciences, University College London, London, UK
- Department of Life Sciences, The Natural History Museum, London SW7 5BD, UK
| | - Molly C. Womack
- Department of Biology, Utah State University, Logan, UT 84322, USA
- Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560-0162, USA
| | - David J. Gower
- Department of Life Sciences, The Natural History Museum, London SW7 5BD, UK
| | | | - Brett Clark
- Imaging and Analysis Centre, The Natural History Museum, London SW7 5BD, UK
| | - Rayna C. Bell
- Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560-0162, USA
- Department of Herpetology, California Academy of Sciences, San Francisco, CA 94118, USA
| | - Ryan K. Schott
- Department of Vertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560-0162, USA
- Department of Biology and Centre for Vision Research, York University, Toronto, Ontario, Canada
| | - Matthew K. Fujita
- Department of Biology, Amphibian and Reptile Diversity Research Center, The University of Texas at Arlington, Arlington, TX 76019, USA
| | - Kate N. Thomas
- Department of Life Sciences, The Natural History Museum, London SW7 5BD, UK
- Department of Biology, Amphibian and Reptile Diversity Research Center, The University of Texas at Arlington, Arlington, TX 76019, USA
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2
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Abstract
For centuries, the eye has fascinated scientists and philosophers alike, and as a result the visual system has always been at the forefront of integrating cutting-edge technology in research. We are again at a turning point at which technical advances have expanded the range of organisms we can study developmentally and deepened what we can learn. In this new era, we are finally able to understand eye development in animals across the phylogenetic tree. In this Review, we highlight six areas in comparative visual system development that address questions that are important for understanding the developmental basis of evolutionary change. We focus on the opportunities now available to biologists to study the developmental genetics, cell biology and morphogenesis that underlie the incredible variation of visual organs found across the Metazoa. Although decades of important work focused on gene expression has suggested homologies and potential evolutionary relationships between the eyes of diverse animals, it is time for developmental biologists to move away from this reductive approach. We now have the opportunity to celebrate the differences and diversity in visual organs found across animal development, and to learn what it can teach us about the fundamental principles of biological systems and how they are built.
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Affiliation(s)
- Kristen M Koenig
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
- John Harvard Distinguished Science Fellowship Program, Harvard University, Cambridge, MA 02138, USA
| | - Jeffrey M Gross
- Departments of Ophthalmology and Developmental Biology, Louis J. Fox Center for Vision Restoration, The University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA
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3
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Three-dimensional data capture and analysis of intact eye lenses evidences emmetropia-associated changes in epithelial cell organization. Sci Rep 2020; 10:16898. [PMID: 33037268 PMCID: PMC7547080 DOI: 10.1038/s41598-020-73625-9] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Accepted: 09/17/2020] [Indexed: 01/16/2023] Open
Abstract
Organ and tissue development are highly coordinated processes; lens growth and functional integration into the eye (emmetropia) is a robust example. An epithelial monolayer covers the anterior hemisphere of the lens, and its organization is the key to lens formation and its optical properties throughout all life stages. To better understand how the epithelium supports lens function, we have developed a novel whole tissue imaging system using conventional confocal light microscopy and a specialized analysis software to produce three-dimensional maps for the epithelium of intact mouse lenses. The open source software package geometrically determines the anterior pole position, the equatorial diameter, and three-dimensional coordinates for each detected cell in the epithelium. The user-friendly cell maps, which retain global lens geometry, allow us to document age-dependent changes in the C57/BL6J mouse lens cell distribution characteristics. We evidence changes in epithelial cell density and distribution in C57/BL6J mice during the establishment of emmetropia between postnatal weeks 4-6. These epithelial changes accompany a previously unknown spheroid to lentoid shape transition of the lens as detected by our analyses. When combined with key findings from previous mouse genetic and cell biological studies, we suggest a cytoskeleton-based mechanism likely underpins these observations.
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4
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Canei J, Burtea C, Nonclercq D. Comparative study of the visual system of two psammophilic lizards (Scincus scincus &Eumeces schneideri). Vision Res 2020; 171:17-30. [PMID: 32360540 DOI: 10.1016/j.visres.2020.04.004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Revised: 04/17/2020] [Accepted: 04/17/2020] [Indexed: 11/30/2022]
Abstract
Sand deserts are common biotopes on the earth's surface. Some specialized vertebrate species have colonized these ecological habitats by living buried in the sand. Among these so called psammophilic species are the Scincidae sand dune living species Scincus scincus and Eumeces schneideri. These two skinks share a relatively similar behavioral ecology by living buried in sand, almost all the time for S. scincus and at least for some part of the day for E. schneideri. The visual system of these two lizards was investigated by histological, immunohistochemical, Magnetic Resonance Imaging (MRI) and morphometric techniques. Both skink species exhibit a retina lacking fovea, composed predominantly of cones presenting two types of oil droplets (pale blue-green and colorless). Both species possess a subset of rod like-photoreceptors (about 1 rod for 30 cones) evidenced by anti-rhodopsin immunoreactivity. A ratio 1:1-1:2 between ganglion cells and photoreceptors points to a linear connection (photoreceptors/bipolar neurons/ganglion cells) in the retina and indicates that both skinks more likely possess good visual acuity, even in the peripheral retina. The MRI analysis revealed differences between the species concerning the eye structures, with a more spherical eye shape for S. scincus, as well as a more flattened lens. The relative lens diameter of both species seems to correspond to a rather photopic pattern. Beside the fact that S. scincus and E. schneideri have different lifestyles, their visual capacities seem similar, and, generally speaking, these two psammophilic species theoretically exhibit visual capacities not far away from non-fossorial species.
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Affiliation(s)
- Jérôme Canei
- Laboratory of Histology, Biosciences Institute, Faculty of Medicine and Pharmacy, University of Mons, 23, Place du Parc, B-7000 Mons, Belgium
| | - Carmen Burtea
- Department of General, Organic and Biomedical Chemistry, NMR and Molecular Imaging Laboratory, University of Mons, B-7000 Mons, Belgium
| | - Denis Nonclercq
- Laboratory of Histology, Biosciences Institute, Faculty of Medicine and Pharmacy, University of Mons, 23, Place du Parc, B-7000 Mons, Belgium.
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5
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Swafford AJM, Oakley TH. Light-induced stress as a primary evolutionary driver of eye origins. Integr Comp Biol 2020; 59:739-750. [PMID: 31539028 DOI: 10.1093/icb/icz064] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Eyes are quintessential complex traits and our understanding of their evolution guides models of trait evolution in general. A long-standing account of eye evolution argues natural selection favors morphological variations that allow increased functionality for sensing light. While certainly true in part, this focus on visual performance does not entirely explain why diffuse photosensitivity persists even after eyes evolve, or why eyes evolved many times, each time using similar building blocks. Here, we briefly review a vast literature indicating most genetic components of eyes historically responded to stress caused directly by light, including ultraviolet damage of DNA, oxidative stress, and production of aldehydes. We propose light-induced stress had a direct and prominent role in the evolution of eyes by bringing together genes to repair and prevent damage from light-stress, both before and during the evolution of eyes themselves. Stress-repair and stress-prevention genes were perhaps originally deployed as plastic responses to light and/or as beneficial mutations genetically driving expression where light was prominent. These stress-response genes sense, shield, and refract light but only as reactions to ongoing light stress. Once under regulatory-genetic control, they could be expressed before light stress appeared, evolve as a module, and be influenced by natural selection to increase functionality for sensing light, ultimately leading to complex eyes and behaviors. Recognizing the potentially prominent role of stress in eye evolution invites discussions of plasticity and assimilation and provides a hypothesis for why similar genes are repeatedly used in convergent eyes. Broadening the drivers of eye evolution encourages consideration of multi-faceted mechanisms of plasticity/assimilation and mutation/selection for complex novelties and innovations in general.
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Affiliation(s)
- Andrew J M Swafford
- Ecology, Evolution, and Marine Biology Department, University of California Santa Barbara, Santa Barbara, CA 93106, USA
| | - Todd H Oakley
- Ecology, Evolution, and Marine Biology Department, University of California Santa Barbara, Santa Barbara, CA 93106, USA
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6
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Evolution of the vertebrate corneal stroma. Prog Retin Eye Res 2018; 64:65-76. [DOI: 10.1016/j.preteyeres.2018.01.002] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2017] [Revised: 01/12/2018] [Accepted: 01/15/2018] [Indexed: 12/14/2022]
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7
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Suzuki TK. On the Origin of Complex Adaptive Traits: Progress Since the Darwin Versus Mivart Debate. JOURNAL OF EXPERIMENTAL ZOOLOGY PART B-MOLECULAR AND DEVELOPMENTAL EVOLUTION 2017; 328:304-320. [PMID: 28397400 DOI: 10.1002/jez.b.22740] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2016] [Revised: 03/02/2017] [Accepted: 03/07/2017] [Indexed: 01/12/2023]
Abstract
The evolutionary origin of complex adaptive traits has been a controversial topic in the history of evolutionary biology. Although Darwin argued for the gradual origins of complex adaptive traits within the theory of natural selection, Mivart insisted that natural selection could not account for the incipient stages of complex traits. The debate starting from Darwin and Mivart eventually engendered two opposite views: gradualism and saltationism. Although this has been a long-standing debate, the issue remains unresolved. However, recent studies have interrogated classic examples of complex traits, such as the asymmetrical eyes of flatfishes and leaf mimicry of butterfly wings, whose origins were debated by Darwin and Mivart. Here, I review recent findings as a starting point to provide a modern picture of the evolution of complex adaptive traits. First, I summarize the empirical evidence that unveils the evolutionary steps toward complex traits. I then argue that the evolution of complex traits could be understood within the concept of "reducible complexity." Through these discussions, I propose a conceptual framework for the formation of complex traits, named as reducible-composable multicomponent systems, that satisfy two major characteristics: reducibility into a sum of subcomponents and composability to construct traits from various additional and combinatorial arrangements of the subcomponents. This conceptual framework provides an analytical foundation for exploring evolutionary pathways to build up complex traits. This review provides certain essential avenues for deciphering the origin of complex adaptive traits.
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Affiliation(s)
- Takao K Suzuki
- Transgenic Silkworm Research Unit, Division of Biotechnology, Institute of Agrobiological Sciences, NARO, Ibaraki, 305-8634, Japan
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8
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Barnes S, Quinlan RA. Small molecules, both dietary and endogenous, influence the onset of lens cataracts. Exp Eye Res 2016; 156:87-94. [PMID: 27039707 DOI: 10.1016/j.exer.2016.03.024] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Revised: 03/18/2016] [Accepted: 03/28/2016] [Indexed: 12/11/2022]
Abstract
How the lens ages successfully is a lesson in biological adaption and the emergent properties of its complement of cells and proteins. This living tissue contains some of the oldest proteins in our bodies and yet they remain functional for decades, despite exposure to UV light, to reactive oxygen species and all the other hazards to protein function. This remarkable feat is achieved by a shrewd investment in very stable proteins as lens crystallins, by providing a reservoir of ATP-independent protein chaperones unequalled by any other tissue and by an oxidation-resistant environment. In addition, glutathione, a free radical scavenger, is present in mM concentrations and the plasma membranes contain oxidation-resistant sphingolipids what compromises lens function as it ages? In this review, we examine the role of small molecules in the prevention or causation of cataracts, including those associated with diet, metabolic pathways and drug therapy (steroids).
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Affiliation(s)
- Stephen Barnes
- Department of Pharmacology and Toxicology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - Roy A Quinlan
- Biophysical Sciences Institute, University of Durham, Durham DH1 3LE, UK; University of Durham, Durham DH1 3LE, UK.
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9
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Wu JJ, Wu W, Tholozan FM, Saunter CD, Girkin JM, Quinlan RA. A dimensionless ordered pull-through model of the mammalian lens epithelium evidences scaling across species and explains the age-dependent changes in cell density in the human lens. J R Soc Interface 2016; 12:20150391. [PMID: 26236824 PMCID: PMC4528606 DOI: 10.1098/rsif.2015.0391] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
We present a mathematical (ordered pull-through; OPT) model of the cell-density profile for the mammalian lens epithelium together with new experimental data. The model is based upon dimensionless parameters, an important criterion for inter-species comparisons where lens sizes can vary greatly (e.g. bovine (approx. 18 mm); mouse (approx. 2 mm)) and confirms that mammalian lenses scale with size. The validated model includes two parameters: β/α, which is the ratio of the proliferation rate in the peripheral and in the central region of the lens; and γGZ, a dimensionless pull-through parameter that accounts for the cell transition and exit from the epithelium into the lens body. Best-fit values were determined for mouse, rat, rabbit, bovine and human lens epithelia. The OPT model accounts for the peak in cell density at the periphery of the lens epithelium, a region where cell proliferation is concentrated and reaches a maximum coincident with the germinative zone. The β/α ratio correlates with the measured FGF-2 gradient, a morphogen critical to lens cell survival, proliferation and differentiation. As proliferation declines with age, the OPT model predicted age-dependent changes in cell-density profiles, which we observed in mouse and human lenses.
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Affiliation(s)
- Jun Jie Wu
- Biophysical Sciences Institute and School of Engineering and Computing Sciences, Durham University, Durham DH1 3LE, UK
- e-mail:
| | - Weiju Wu
- Biophysical Sciences Institute and School of Biological and Biomedical Sciences, Durham University, Durham DH1 3LE, UK
| | - Frederique M. Tholozan
- Biophysical Sciences Institute and School of Biological and Biomedical Sciences, Durham University, Durham DH1 3LE, UK
| | - Christopher D. Saunter
- Biophysical Sciences Institute and Department of Physics, Durham University, Durham DH1 3LE, UK
| | - John M. Girkin
- Biophysical Sciences Institute and Department of Physics, Durham University, Durham DH1 3LE, UK
| | - Roy A. Quinlan
- Biophysical Sciences Institute and School of Biological and Biomedical Sciences, Durham University, Durham DH1 3LE, UK
- e-mail:
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10
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Markiewicz E, Barnard S, Haines J, Coster M, van Geel O, Wu W, Richards S, Ainsbury E, Rothkamm K, Bouffler S, Quinlan RA. Nonlinear ionizing radiation-induced changes in eye lens cell proliferation, cyclin D1 expression and lens shape. Open Biol 2016; 5:150011. [PMID: 25924630 PMCID: PMC4422125 DOI: 10.1098/rsob.150011] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Elevated cataract risk after radiation exposure was established soon after the discovery of X-rays in 1895. Today, increased cataract incidence among medical imaging practitioners and after nuclear incidents has highlighted how little is still understood about the biological responses of the lens to low-dose ionizing radiation (IR). Here, we show for the first time that in mice, lens epithelial cells (LECs) in the peripheral region repair DNA double strand breaks (DSB) after exposure to 20 and 100 mGy more slowly compared with circulating blood lymphocytes, as demonstrated by counts of γH2AX foci in cell nuclei. LECs in the central region repaired DSBs faster than either LECs in the lens periphery or lymphocytes. Although DSB markers (γH2AX, 53BP1 and RAD51) in both lens regions showed linear dose responses at the 1 h timepoint, nonlinear responses were observed in lenses for EdU (5-ethynyl-2′-deoxy-uridine) incorporation, cyclin D1 staining and cell density after 24 h at 100 and 250 mGy. After 10 months, the lens aspect ratio was also altered, an indicator of the consequences of the altered cell proliferation and cell density changes. A best-fit model demonstrated a dose-response peak at 500 mGy. These data identify specific nonlinear biological responses to low (less than 1000 mGy) dose IR-induced DNA damage in the lens epithelium.
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Affiliation(s)
- Ewa Markiewicz
- School of Biological and Biomedical Sciences, University of Durham, Durham DH1 3LE, UK
| | - Stephen Barnard
- Public Health England, Centre for Radiation, Chemical & Environmental Hazards, Chilton, Didcot, Oxon OX11 0RQ, UK
| | - Jackie Haines
- Public Health England, Centre for Radiation, Chemical & Environmental Hazards, Chilton, Didcot, Oxon OX11 0RQ, UK
| | - Margaret Coster
- Public Health England, Centre for Radiation, Chemical & Environmental Hazards, Chilton, Didcot, Oxon OX11 0RQ, UK
| | - Orry van Geel
- School of Biological and Biomedical Sciences, University of Durham, Durham DH1 3LE, UK Faculty of Science, KU Leuven, Kasteelpark Arenberg 11, Leuven 3001, Belgium
| | - Weiju Wu
- School of Biological and Biomedical Sciences, University of Durham, Durham DH1 3LE, UK Biophysical Sciences Institute, University of Durham, Durham DH1 3LE, UK
| | - Shane Richards
- School of Biological and Biomedical Sciences, University of Durham, Durham DH1 3LE, UK
| | - Elizabeth Ainsbury
- Public Health England, Centre for Radiation, Chemical & Environmental Hazards, Chilton, Didcot, Oxon OX11 0RQ, UK
| | - Kai Rothkamm
- Public Health England, Centre for Radiation, Chemical & Environmental Hazards, Chilton, Didcot, Oxon OX11 0RQ, UK
| | - Simon Bouffler
- Public Health England, Centre for Radiation, Chemical & Environmental Hazards, Chilton, Didcot, Oxon OX11 0RQ, UK
| | - Roy A Quinlan
- School of Biological and Biomedical Sciences, University of Durham, Durham DH1 3LE, UK Biophysical Sciences Institute, University of Durham, Durham DH1 3LE, UK
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11
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Oakley TH, Speiser DI. How Complexity Originates: The Evolution of Animal Eyes. ANNUAL REVIEW OF ECOLOGY EVOLUTION AND SYSTEMATICS 2015. [DOI: 10.1146/annurev-ecolsys-110512-135907] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Todd H. Oakley
- Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, California 93106;
| | - Daniel I. Speiser
- Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208
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12
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Courtney R, Sachlikidis N, Jones R, Seymour J. Prey Capture Ecology of the Cubozoan Carukia barnesi. PLoS One 2015; 10:e0124256. [PMID: 25970583 PMCID: PMC4429964 DOI: 10.1371/journal.pone.0124256] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2015] [Accepted: 03/11/2015] [Indexed: 12/16/2022] Open
Abstract
Adult Carukia barnesi medusae feed predominantly on larval fish; however, their mode of prey capture seems more complex than previously described. Our findings revealed that during light conditions, this species extends its tentacles and ‘twitches’ them frequently. This highlights the lure-like nematocyst clusters in the water column, which actively attract larval fish that are consequently stung and consumed. This fishing behavior was not observed during dark conditions, presumably to reduce energy expenditure when they are not luring visually oriented prey. We found that larger medusae have longer tentacles; however, the spacing between the nematocyst clusters is not dependent on size, suggesting that the spacing of the nematocyst clusters is important for prey capture. Additionally, larger specimens twitch their tentacles more frequently than small specimens, which correlate with their recent ontogenetic prey shift from plankton to larval fish. These results indicate that adult medusae of C. barnesi are not opportunistically grazing in the water column, but instead utilize sophisticated prey capture techniques to specifically target larval fish.
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Affiliation(s)
- Robert Courtney
- Australian Institute of Tropical Health and Medicine, James Cook University, Cairns, Queensland, Australia
- * E-mail:
| | | | - Rhondda Jones
- College of Marine & Environmental Sciences, James Cook University, Townsville, Queensland, Australia
| | - Jamie Seymour
- Australian Institute of Tropical Health and Medicine, James Cook University, Cairns, Queensland, Australia
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13
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Mochizuki T, Masai I. The lens equator: a platform for molecular machinery that regulates the switch from cell proliferation to differentiation in the vertebrate lens. Dev Growth Differ 2014; 56:387-401. [PMID: 24720470 DOI: 10.1111/dgd.12128] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2014] [Revised: 02/20/2014] [Accepted: 02/21/2014] [Indexed: 01/17/2023]
Abstract
The vertebrate lens is a transparent, spheroidal tissue, located in the anterior region of the eye that focuses visual images on the retina. During development, surface ectoderm associated with the neural retina invaginates to form the lens vesicle. Cells in the posterior half of the lens vesicle differentiate into primary lens fiber cells, which form the lens fiber core, while cells in the anterior half maintain a proliferative state as a monolayer lens epithelium. After formation of the primary fiber core, lens epithelial cells start to differentiate into lens fiber cells at the interface between the lens epithelium and the primary lens fiber core, which is called the equator. Differentiating lens fiber cells elongate and cover the old lens fiber core, resulting in growth of the lens during development. Thus, lens fiber differentiation is spatially regulated and the equator functions as a platform that regulates the switch from cell proliferation to cell differentiation. Since the 1970s, the mechanism underlying lens fiber cell differentiation has been intensively studied, and several regulatory factors that regulate lens fiber cell differentiation have been identified. In this review, we focus on the lens equator, where these regulatory factors crosstalk and cooperate to regulate lens fiber differentiation. Normally, lens epithelial cells must pass through the equator to start lens fiber differentiation. However, there are reports that when the lens epithelium structure is collapsed, lens fiber cell differentiation occurs without passing the equator. We also discuss a possible mechanism that represses lens fiber cell differentiation in lens epithelium.
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Affiliation(s)
- Toshiaki Mochizuki
- Developmental Neurobiology Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna, Okinawa, 904-0495, Japan
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14
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Wassmer S, Beddaoui M, Rajai P, Munger R, Tsilfidis C. A focus on the optical properties of the regenerated newt lens. PLoS One 2013; 8:e70845. [PMID: 23990914 PMCID: PMC3750027 DOI: 10.1371/journal.pone.0070845] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2013] [Accepted: 06/25/2013] [Indexed: 11/30/2022] Open
Abstract
Lens regeneration studies in the adult newt suggest that molecular aspects of lens regeneration are complete within 5 weeks of lentectomy. However, very little is known about the optical properties of the regenerated lens. In an aquatic environment, the lens accounts for almost all of the refractive power of the eye, and thus, a fully functional lens is critical. We compared the optical properties of 9- and 26-week regenerated lenses in the red spotted newt, Notophthalmus viridescens, with the original lenses removed from the same eyes. At 9 weeks, the regenerated lenses are smaller than the original lenses and are histologically immature, with a lower density of lens proteins. The 9 week lenses have greater light transmission, but significantly reduced focal length and refractive index than the original lenses. This suggests that following 9 weeks of regeneration, the lenses have not recovered the functionality of the original lens. By 26 weeks, the transmission of light in the more mature lens is reduced, but the optical parameters of the lens have recovered enough to allow functional vision.
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Affiliation(s)
- Sarah Wassmer
- Ottawa Hospital Research Institute, Vision Research Program, Ottawa, Ontario, Canada
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Margaret Beddaoui
- Ottawa Hospital Research Institute, Vision Research Program, Ottawa, Ontario, Canada
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Payman Rajai
- Ottawa Hospital Research Institute, Vision Research Program, Ottawa, Ontario, Canada
- Department of Physics, University of Ottawa, Ottawa, Ontario, Canada
| | - Réjean Munger
- Ottawa Hospital Research Institute, Vision Research Program, Ottawa, Ontario, Canada
- Department of Physics, University of Ottawa, Ottawa, Ontario, Canada
- Department of Ophthalmology, University of Ottawa, Ottawa, Ontario, Canada
| | - Catherine Tsilfidis
- Ottawa Hospital Research Institute, Vision Research Program, Ottawa, Ontario, Canada
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
- Department of Ophthalmology, University of Ottawa, Ottawa, Ontario, Canada
- * E-mail:
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