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          Institute: MPI für Entwicklungsbiologie     Collection: Abteilungsunabhängige Arbeitsgruppen     Display Documents

ID: 733154.0, MPI für Entwicklungsbiologie / Abteilungsunabhängige Arbeitsgruppen
Phototaxis and the origin of visual eyes
Authors:Randel, N.; Jekely, G.
Date of Publication (YYYY-MM-DD):2016-01-05
Title of Journal:Philos Trans R Soc Lond B Biol Sci
Issue / Number:1685
Sequence Number of Article:20150042
Review Status:Internal review
Audience:Not Specified
Abstract / Description:Vision allows animals to detect spatial differences in environmental light levels. High-resolution image-forming eyes evolved from low-resolution eyes via increases in photoreceptor cell number, improvements in optics and changes in the neural circuits that process spatially resolved photoreceptor input. However, the evolutionary origins of the first low-resolution visual systems have been unclear. We propose that the lowest resolving (two-pixel) visual systems could initially have functioned in visual phototaxis. During visual phototaxis, such elementary visual systems compare light on either side of the body to regulate phototactic turns. Another, even simpler and non-visual strategy is characteristic of helical phototaxis, mediated by sensory-motor eyespots. The recent mapping of the complete neural circuitry (connectome) of an elementary visual system in the larva of the annelid Platynereis dumerilii sheds new light on the possible paths from non-visual to visual phototaxis and to image-forming vision. We outline an evolutionary scenario focusing on the neuronal circuitry to account for these transitions. We also present a comprehensive review of the structure of phototactic eyes in invertebrate larvae and assign them to the non-visual and visual categories. We propose that non-visual systems may have preceded visual phototactic systems in evolution that in turn may have repeatedly served as intermediates during the evolution of image-forming eyes.
Free Keywords:Animals; *Biological Evolution; Eye/*anatomy & histology; Gene Expression Regulation; Opsins/genetics/metabolism; Photoreceptor Cells/*physiology; connectome; eye evolution; marine ciliated larva; opsin; photoreceptor; vision
External Publication Status:published
Document Type:Article
Affiliations:MPI für Entwicklungsbiologie/Abteilungsunabhängige Arbeitsgruppen/Arbeitsgruppe Jekely
External Affiliations:Max Planck Institute for Developmental Biology, Spemannstrasse 35, 72076 Tubingen, Germany gaspar.jekely@tuebingen.mpg.de.
Identifiers:ISSN:1471-2970 (Electronic) 0962-8436 (Linking) %R 10.1... [ID No:1]
URL:https://www.ncbi.nlm.nih.gov/pubmed/26598725 [ID No:2]
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