The shell-eyes of the chiton Acanthopleura granulata (Mollusca, Polyplacophora) use pheomelanin as a screening pigment

Certain species of chiton (Mollusca, Polyplacophora) have hundreds of small (< 100 µm) eyes embedded in their dorsal shell plates. These eyes each contain a retina, a layer of screening pigment, and a lens. Previously, we demonstrated that the eyes of chitons provide spatial vision. As in other camera-type eyes, the screening pigments in the eyes of chitons absorb off-axis light in order to preserve the contrast of images formed on the retina. Our results indicate that the red-brown, alkali-soluble screening pigment associated with the eyes of the chiton Acanthopleura granulata (Gmelin, 1791) is pheomelanin. Using high-performance liquid chromatography (HPLC) and MALDI-TOF mass spectroscopy, we find that degrading A. granulata’s screening pigment with alkaline hydrogen peroxide produces 6-(2-amino-2-carboxyethyl)-2-carboxy-4-hydroxybenzothiazole (BTCA), a diagnostic marker of pheomelanin. Chitons are the first molluscs demonstrated to use pheomelanin as a screening pigment in their eyes. Our results suggest that the image-forming eyes of chitons may have evolved separately from eyes that employ different types of screening pigment, such as those of most other invertebrates. Further, we hypothesize that change in the expression pattern of tyrosinase – an enzyme responsible for melanin synthesis in many other metazoans – may have contributed to the origin of screening pigments in chitons, a critical step in the evolution of their eyes.

[1]  J. Sigwart,et al.  Chiton phylogeny (Mollusca : Polyplacophora) and the placement of the enigmatic species Choriplax grayi (H. Adams & Angas) , 2013, Invertebrate Systematics.

[2]  K. Wakamatsu,et al.  Melanins and melanogenesis: methods, standards, protocols , 2013, Pigment cell & melanoma research.

[3]  N. Gompel,et al.  Emergence and Diversification of Fly Pigmentation Through Evolution of a Gene Regulatory Module , 2013, Science.

[4]  D. Nilsson,et al.  Eye evolution and its functional basis , 2013, Visual Neuroscience.

[5]  D. Arendt,et al.  Molecular analysis of the amphioxus frontal eye unravels the evolutionary origin of the retina and pigment cells of the vertebrate eye , 2012, Proceedings of the National Academy of Sciences.

[6]  G. Ghanem,et al.  Has removal of excess cysteine led to the evolution of pheomelanin? , 2012, BioEssays : news and reviews in molecular, cellular and developmental biology.

[7]  P. Riley,et al.  Melanins and Melanosomes: Biosynthesis, Biogenesis, Physiological, and Pathological Functions , 2011 .

[8]  S. Johnsen,et al.  A Chiton Uses Aragonite Lenses to Form Images , 2011, Current Biology.

[9]  M. Riou,et al.  Cryptic Color Change in a Crab Spider (Misumena vatia): Identification and Quantification of Precursors and Ommochrome Pigments by HPLC , 2010, Journal of Chemical Ecology.

[10]  Z. Kozmík,et al.  Eye evolution: common use and independent recruitment of genetic components , 2009, Philosophical Transactions of the Royal Society B: Biological Sciences.

[11]  B. Morton,et al.  The fine structure of the pallial eyes of Laternula truncata (Bivalvia: Anomalodesmata: Pandoracea) , 2009 .

[12]  Detlev Arendt,et al.  Eye Evolution: The Blurry Beginning , 2008, Current Biology.

[13]  Claudia C. Johnson,et al.  The effect of sampling bias on the fossil record of chitons (Mollusca, Polyplacophora)* , 2008 .

[14]  Cestmir Vlcek,et al.  Assembly of the cnidarian camera-type eye from vertebrate-like components , 2008, Proceedings of the National Academy of Sciences.

[15]  D. Eernisse,et al.  Aesthete canal morphology in the Mopaliidae (Polyplacophora)* , 2008 .

[16]  Manfred Schartl,et al.  Evolution of pigment synthesis pathways by gene and genome duplication in fish , 2007, BMC Evolutionary Biology.

[17]  G. Monfrecola,et al.  An easy-to-run method for routine analysis of eumelanin and pheomelanin in pigmented tissues. , 2007, Pigment cell research.

[18]  Masato Yano,et al.  Tyrosinase localization in mollusc shells. , 2007, Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology.

[19]  H. Hoekstra.  Genetics, development and evolution of adaptive pigmentation in vertebrates , 2006, Heredity.

[20]  S. Hase,et al.  Characterization of the pigment produced by the planarian, Dugesia ryukyuensis. , 2006, Pigment cell research.

[21]  B. Sirenko.  New outlook on the system of chitons (Mollusca: Polyplacophora) , 2006 .

[22]  Keisuke Takeuchi,et al.  A Genome-Wide Survey of Genes for Enzymes Involved in Pigment Synthesis in an Ascidian, Ciona intestinalis , 2005, Zoological science.

[23]  K. McGraw.  The antioxidant function of many animal pigments: are there consistent health benefits of sexually selected colourants? , 2005, Animal Behaviour.

[24]  H. Mori,et al.  Purification, characterization and molecular cloning of tyrosinase from the cephalopod mollusk, Illex argentinus. , 2003, European journal of biochemistry.

[25]  Artyom Kopp,et al.  Evolution in black and white: genetic control of pigment patterns in Drosophila. , 2003, Trends in genetics : TIG.

[26]  I. Ziegler,et al.  The pteridine pathway in zebrafish: regulation and specification during the determination of neural crest cell-fate. , 2003, Pigment cell research.

[27]  M. Sugumaran.  Comparative biochemistry of eumelanogenesis and the protective roles of phenoloxidase and melanin in insects. , 2002, Pigment cell research.

[28]  S. Sato,et al.  Development of pigment cells in the brain of ascidian tadpole larvae: insights into the origins of vertebrate pigment cells. , 2001, Pigment cell research.

[29]  P. Riley.  Molecules in focusMelanin , 1997 .

[30]  V. del Marmol,et al.  Tyrosinase and related proteins in mammalian pigmentation , 1996, FEBS letters.

[31]  M. Porcar,et al.  Identification of pteridines in the firebug, Pyrrhocoris apterus (L.) (Heteroptera, Pyrrhocoridae) by high -performance liquid chromatography , 1996 .

[32]  J. Baxter,et al.  The ultrastructure of the aesthetes of Leptochiton asellus (Polyplacophora: Lepidopleurina) , 1993 .

[33]  J. Baxter,et al.  The structure of the intrapigmented aesthetes and the properiostracum layer in Callochiton achatinus (Mollusca: Polyplacophora) , 1990 .

[34]  J. Baxter,et al.  The infrastructure of aesthetes in Tonicella marmorea (Polyplacophora; Ischnochitonina) and a new functional hypothesis , 1987 .

[35]  R. M. Eakin,et al.  Pinocytosis in eyes of a snail, Helix aspersa. , 1982, Journal of ultrastructure research.

[36]  C. Weber.  Structure, histochemistry, ontogenetic development, and regeneration of the ocellus of Cladonema radiatum dujardin (cnidaria, hydrozoa, anthomedusae) , 1981, Journal of morphology.

[37]  K. Kriesten,et al.  Die Ästheten mit intrapigmentärem Schalenauge vonChiton marmoratus L. (Mollusca, Placophora) , 1978, Zoomorphologie.

[38]  P. Boyle,et al.  The aesthetes of chitons , 1976, Cell and Tissue Research.

[39]  R. M. Eakin,et al.  Understanding A Snail's Eye at a Snail's Pace , 1975 .

[40]  N. A. Croll,et al.  Comparative nematode photoreceptors. , 1975, Comparative biochemistry and physiology. A, Comparative physiology.

[41]  R. M. Eakin,et al.  Fine structure of the eyes of an alciopid polychaete, Vanadis tagensis (Annelida) , 1974, Zeitschrift für Morphologie der Tiere.

[42]  P. Boyle.  The aesthetes of chitons: 1. Role in the light response of whole animals , 1972 .

[43]  J. A. Westfall,et al.  FINE STRUCTURE OF PHOTORECEPTORS IN THE HYDROMEDUSAN, POLYORCHIS PENICILLATUS. , 1962, Proceedings of the National Academy of Sciences of the United States of America.

[44]  P. Riley,et al.  Comprar Melanins And Melanosomes: Biosynthesis, Biogenesis, Physiological, And Pathological Functions | Patrick A. Riley | 9783527328925 | Wiley , 2011 .

[45]  B. Runnegar,et al.  Aesthete canal morphology in twelve species of chiton (Polyplacophora) , 2007 .

[46]  G. Edwards,et al.  Oxidation Potentials of Human Eumelanosomes and Pheomelanosomes¶ , 2005, Photochemistry and photobiology.

[47]  P. Boyle,et al.  Fine structure of the eyes of Onithochiton neglectus (Mollusca: Polyplacophora) , 2004, Zeitschrift für Zellforschung und Mikroskopische Anatomie.

[48]  Gonzalo Giribet,et al.  Towards a phylogeny of chitons (Mollusca, Polyplacophora) based on combined analysis of five molecular loci , 2003 .

[49]  F. Fischer.  Photorezeptor cells in Chiton aesthetes (Mollusca, Polyplacophora, Chitonidae) , 1978 .

[50]  L. Hyman,et al.  The Invertebrates: Mollusca I , 1968 .

[51]  M. Wiener,et al.  Animal eyes. , 1957, The American orthoptic journal.

[52]  H. N. Moseley.  Memoirs: On the Presence of Eyes in the Shells of Certain Chitonidæ, and on the Structure of these Organs , 1885 .