title: Seeing red to being red: conserved genetic mechanism for red cone oil droplets and co-option for red coloration in birds and turtles.
abstract: Avian ketocarotenoid pigments occur in both the red retinal oil droplets that contribute to colour vision and bright red coloration used in signalling. Turtles are the only other tetrapods with red retinal oil droplets, and some also display red carotenoid-based coloration. Recently, the CYP2J19 gene was strongly implicated in ketocarotenoid synthesis in birds. Here, we investigate CYP2J19 evolution in relation to colour vision and red coloration in reptiles using genomic and expression data. We show that turtles, but not crocodiles or lepidosaurs, possess a CYP2J19 orthologue, which arose via gene duplication before turtles and archosaurs split, and which is strongly and specifically expressed in the ketocarotenoid-containing retina and red integument. We infer that CYP2J19 initially functioned in colour vision in archelosaurs and conclude that red ketocarotenoid-based coloration evolved independently in birds and turtles via gene regulatory changes of CYP2J19 Our results suggest that red oil droplets contributed to colour vision in dinosaurs and pterosaurs.
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK.
authors.forename: Hanlu
authors.initials: H
authors.lastname: Twyman
authors.affiliation: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, 251 Bessey Hall, Ames, IA 50011, USA.
authors.forename: Nicole
authors.initials: N
authors.lastname: Valenzuela
authors.affiliation: Department of Ecology, Evolution, and Organismal Biology, Iowa State University, 251 Bessey Hall, Ames, IA 50011, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Literman
authors.affiliation: Department of Biological and Environmental Sciences, University of Gothenburg, Göteborg 40530, Sweden.
authors.forename: Staffan
authors.initials: S
authors.lastname: Andersson
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, UK nim21@cam.ac.uk.
authors.forename: Nicholas I
authors.identifier: 0000-0002-5545-1517
authors.initials: NI
authors.lastname: Mundy
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000033:anatomy & histology / Q000235:genetics*; D055253:Color Vision / Q000235:genetics*; D000090762:Cytochrome P-450 CYP2J2; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D010858:Pigmentation; D012160:Retina / Q000033:anatomy & histology; D017949:Retinal Cone Photoreceptor Cells / Q000166:cytology*; D014426:Turtles / Q000033:anatomy & histology / Q000235:genetics*
chemical_list: D003577:Cytochrome P-450 Enzyme System; D000090762:Cytochrome P-450 CYP2J2
keywords: CYP2J; birds; carotenoid coloration; colour vision; retinal oil droplets; turtles