title: Visual pigments in a palaeognath bird, the emu Dromaius novaehollandiae: implications for spectral sensitivity and the origin of ultraviolet vision.
abstract: A comprehensive description of the spectral characteristics of retinal photoreceptors in palaeognaths is lacking. Moreover, controversy exists with respect to the spectral sensitivity of the short-wavelength-sensitive-1 (SWS1) opsin-based visual pigment expressed in one type of single cone: previous microspectrophotometric (MSP) measurements in the ostrich (Struthio camelus) suggested a violet-sensitive (VS) SWS1 pigment, but all palaeognath SWS1 opsin sequences obtained to date (including the ostrich) imply that the visual pigment is ultraviolet-sensitive (UVS). In this study, MSP was used to measure the spectral properties of visual pigments and oil droplets in the retinal photoreceptors of the emu (Dromaius novaehollandiae). Results show that the emu resembles most other bird species in possessing four spectrally distinct single cones, as well as double cones and rods. Four cone and a single rod opsin are expressed, each an orthologue of a previously identified pigment. The SWS1 pigment is clearly UVS (wavelength of maximum absorbance [λmax] = 376 nm), with key tuning sites (Phe86 and Cys90) consistent with other vertebrate UVS SWS1 pigments. Palaeognaths would appear, therefore, to have UVS SWS1 pigments. As they are considered to be basal in avian evolution, this suggests that UVS is the most likely ancestral state for birds. The functional significance of a dedicated UVS cone type in the emu is discussed.
authors.affiliation: Department of Biological Sciences, Macquarie University, North Ryde, New South Wales 2109, Australia School of Animal Biology, University of Western Australia, Crawley, Western Australia 6009, Australia nathan.hart@mq.edu.au.
authors.forename: Nathan S
authors.initials: NS
authors.lastname: Hart
authors.affiliation: School of Animal Biology, University of Western Australia, Crawley, Western Australia 6009, Australia Oceans Institute, University of Western Australia, Crawley, Western Australia 6009, Australia Lions Eye Institute, University of Western Australia, Nedlands, Western Australia 6009, Australia.
authors.forename: Jessica K
authors.initials: JK
authors.lastname: Mountford
authors.affiliation: School of Animal Biology, University of Western Australia, Crawley, Western Australia 6009, Australia Oceans Institute, University of Western Australia, Crawley, Western Australia 6009, Australia Lions Eye Institute, University of Western Australia, Nedlands, Western Australia 6009, Australia.
authors.forename: Wayne I L
authors.initials: WI
authors.lastname: Davies
authors.affiliation: School of Animal Biology, University of Western Australia, Crawley, Western Australia 6009, Australia Oceans Institute, University of Western Australia, Crawley, Western Australia 6009, Australia Lions Eye Institute, University of Western Australia, Nedlands, Western Australia 6009, Australia.
authors.forename: Shaun P
authors.initials: SP
authors.lastname: Collin
authors.affiliation: School of Animal Biology, University of Western Australia, Crawley, Western Australia 6009, Australia Lions Eye Institute, University of Western Australia, Nedlands, Western Australia 6009, Australia.
authors.forename: David M
authors.initials: DM
authors.lastname: Hunt
mesh_terms: D000818:Animals; D020312:Dromaiidae / Q000502:physiology*; D055355:Opsins / Q000502:physiology*; D017949:Retinal Cone Photoreceptor Cells / Q000502:physiology*; D012168:Retinal Pigments / Q000502:physiology*; D014466:Ultraviolet Rays; D014785:Vision, Ocular
chemical_list: D055355:Opsins; D012168:Retinal Pigments
keywords: Casuariiformes; microspectrophotometry; oil droplets; opsin evolution; spectral tuning