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. 2011 Jan 7;278(1702):107-14.
doi: 10.1098/rspb.2010.1100. Epub 2010 Jul 28.

Ultraviolet-sensitive vision in long-lived birds

Livia S Carvalho  1 , Ben Knott, Mathew L Berg, Andrew T D Bennett, David M Hunt
Affiliations

Ultraviolet-sensitive vision in long-lived birds

Livia S Carvalho et al. Proc Biol Sci. .

Abstract

Long-term exposure to ultraviolet (UV) light generates substantial damage, and in mammals, visual sensitivity to UV is restricted to short-lived diurnal rodents and certain marsupials. In humans, the cornea and lens absorb all UV-A and most of the terrestrial UV-B radiation, preventing the reactive and damaging shorter wavelengths from reaching the retina. This is not the case in certain species of long-lived diurnal birds, which possess UV-sensitive (UVS) visual pigments, maximally sensitive below 400 nm. The Order Psittaciformes contains some of the longest lived bird species, and the two species examined so far have been shown to possess UVS pigments. The objective of this study was to investigate the prevalence of UVS pigments across long-lived parrots, macaws and cockatoos, and therefore assess whether they need to cope with the accumulated effects of exposure to UV-A and UV-B over a long period of time. Sequences from the SWS1 opsin gene revealed that all 14 species investigated possess a key substitution that has been shown to determine a UVS pigment. Furthermore, in vitro regeneration data, and lens transparency, corroborate the molecular findings of UV sensitivity. Our findings thus support the claim that the Psittaciformes are the only avian Order in which UVS pigments are ubiquitous, and indicate that these long-lived birds have UV sensitivity, despite the risks of photodamage.

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Figures

Figure 1.
Figure 1.
(a) Platycercus elegans SWS1 protein sequence aligned with budgerigar (GenBank accession no. Y11787), chicken (GenBank accession no. M92039) and pigeon SWS1 (GenBank accession no. AF149234) sequences. Residue 90, Glu113 and Lys296 are labelled. (b) Tree of full-length coding sequences of avian SWS1 opsin genes, showing the correct positioning of the rosella sequence among the avian SWS1 sequences. GenBank accession no.: pigeon SWS1 AH007798; canary SWS1 AJ277922; zebra finch SWS1 NM_001076704; cormorant SWS1 EF568933; chicken SWS2 M92037; chicken Rh1 NM_205490; chicken Rh2 M92038; chicken LWS NM_205409. The tree was generated by neighbour-joining using the Kimura-2 parameter model. The robustness of each branch point is indicated by the bootstrap values. The scale bar indicates the number of nucleotide substitutions per site. The tree was rooted by using the chicken opsins as outgroups.
Figure 2.
Figure 2.
Platycerus elegans wild-type SWS1 opsin pigment regenerated in vitro with 11-cis-retinal and lens transmission. (a) Raw data for the dark- (black circles) and acid-treated (grey triangles) spectra. (b) Difference spectrum (symbols) fitted with the Govardovskii visual pigment standard curve (black line) to give an accurate λmax.
Figure 3.
Figure 3.
Platycerus elegans lens transmission. Right (grey triangles) and left (black circles) eye lenses transparency properties measured by the transmission percentage plotted against wavelength.
Figure 4.
Figure 4.
Amino acid sequences deduced from the partial SWS1 amplicons from 14 parrot species aligned with the corresponding region of the budgerigar sequence. Note that site 86 is occupied by Ala and site 90 by Cys in all species. The transmembrane regions 1–3 are boxed.
See this image and copyright information in PMC

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