Complementary shifts in photoreceptor spectral tuning unlock the full adaptive potential of ultraviolet vision in birds

Matthew B. Toomey, Olle Lind, Rikard Frederiksen, Robert W. Curley Jr, Ken M. Riedl, David Wilby, Steven J. Schwartz, Christopher C. Witt, Earl H. Harrison, Nicholas Roberts, Misha Vorobyev, Kevin McGraw, M Carter Cornwall, Almut Kelber, Joseph Corbo

Research output: Contribution to journalArticle (Academic Journal)

28 Citations (Scopus)
292 Downloads (Pure)

Abstract

Color vision in birds is mediated by four types of cone photoreceptors whose maximal sensitivities (λmax) are evenly spaced across the light spectrum. In the course of avian evolution, the λmax of the most shortwave-sensitive cone, SWS1, has switched between violet (λmax > 400 nm) and ultraviolet (λmax < 380 nm) multiple times. This shift of the SWS1 opsin is accompanied by a corresponding short-wavelength shift in the spectrally adjacent SWS2 cone. Here, we show that SWS2 cone spectral tuning is mediated by modulating the ratio of two apocarotenoids, galloxanthin and 11’,12’-dihydrogalloxanthin, which act as intracellular spectral filters in the SWS2 cone. We propose an enzymatic pathway that mediates the differential production of these apocarotenoids in the avian retina, and we use color vision modeling to demonstrate how correlated evolution of spectral tuning is necessary to achieve even sampling of the light spectrum and thereby maintain near-optimal color discrimination.
Original languageEnglish
Article numbere15675
Number of pages27
JournaleLife
Volume5
DOIs
Publication statusPublished - 12 Jul 2016

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