title: Spectral sensitivity in Onychophora (velvet worms) revealed by electroretinograms, phototactic behaviour and opsin gene expression.
abstract: Onychophorans typically possess a pair of simple eyes, inherited from the last common ancestor of Panarthropoda (Onychophora+Tardigrada+Arthropoda). These visual organs are thought to be homologous to the arthropod median ocelli, whereas the compound eyes probably evolved in the arthropod lineage. To gain insights into the ancestral function and evolution of the visual system in panarthropods, we investigated phototactic behaviour, opsin gene expression and the spectral sensitivity of the eyes in two representative species of Onychophora: Euperipatoides rowelli (Peripatopsidae) and Principapillatus hitoyensis (Peripatidae). Our behavioural analyses, in conjunction with previous data, demonstrate that both species exhibit photonegative responses to wavelengths ranging from ultraviolet to green light (370-530 nm), and electroretinograms reveal that the onychophoran eye is maximally sensitive to blue light (peak sensitivity ∼480 nm). Template fits to these sensitivities suggest that the onychophoran eye is monochromatic. To clarify which type of opsin the single visual pigment is based on, we localised the corresponding mRNA in the onychophoran eye and brain using in situ hybridization. Our data show that the r-opsin gene (onychopsin) is expressed exclusively in the photoreceptor cells of the eye, whereas c-opsin mRNA is confined to the optic ganglion cells and the brain. Together, our findings suggest that the onychopsin is involved in vision, whereas c-opsin might have a photoreceptive, non-visual function in onychophorans.
authors.affiliation: Department of Animal Evolution and Development, Institute of Biology, University of Leipzig, Talstrasse 33, Leipzig D-04103, Germany Rudolf-Boehm-Institute of Pharmacology and Toxicology, University of Leipzig, Haertelstrasse 16-18, Leipzig D-04107, Germany holger.beckmann@medizin.uni-leipzig.de.
authors.forename: Holger
authors.initials: H
authors.lastname: Beckmann
authors.affiliation: Department of Animal Evolution and Development, Institute of Biology, University of Leipzig, Talstrasse 33, Leipzig D-04103, Germany.
authors.forename: Lars
authors.initials: L
authors.lastname: Hering
authors.affiliation: Department of Biology, Lund University, Sölvegatan 35, Lund 22362, Sweden.
authors.forename: Miriam J
authors.initials: MJ
authors.lastname: Henze
authors.affiliation: Department of Biology, Lund University, Sölvegatan 35, Lund 22362, Sweden.
authors.forename: Almut
authors.initials: A
authors.lastname: Kelber
authors.affiliation: Department of Animal Physiology, Institute of Biology, University of Leipzig, Talstrasse 33, Leipzig D-04103, Germany.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Stevenson
authors.affiliation: Department of Animal Evolution and Development, Institute of Biology, University of Leipzig, Talstrasse 33, Leipzig D-04103, Germany Department of Zoology, Institute of Biology, University of Kassel, Heinrich-Plett-Str. 40, D-34132 Kassel, Germany.
authors.forename: Georg
authors.initials: G
authors.lastname: Mayer
mesh_terms: D000818:Animals; D004596:Electroretinography; D005123:Eye / Q000166:cytology; D005260:Female; D015870:Gene Expression; D017404:In Situ Hybridization, Fluorescence; D007448:Invertebrates / Q000235:genetics / Q000502:physiology*; D008297:Male; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D055355:Opsins / Q000235:genetics* / Q000378:metabolism; D017422:Sequence Analysis, DNA; D014796:Visual Perception
chemical_list: D055355:Opsins
keywords: Arthropod; Evolution; Eye; Light response; Opsins; Phototaxis; Vision