Repository logo

Seeing red to being red: conserved genetic mechanism for red cone oil droplets and co-option for red coloration in birds and turtles.

Accepted version



Change log


Twyman, Hanlu 
Valenzuela, Nicole 
Literman, Robert 
Andersson, Staffan 


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.



CYP2J, birds, carotenoid coloration, colour vision, retinal oil droplets, turtles, Animals, Biological Evolution, Birds, Color Vision, Cytochrome P-450 CYP2J2, Cytochrome P-450 Enzyme System, Pigmentation, Retina, Retinal Cone Photoreceptor Cells, Turtles

Journal Title

Proc Biol Sci

Conference Name

Journal ISSN


Volume Title



The Royal Society
We thank the BBSRC Doctoral Training Partnerships (to H.T.) for funding.