Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Uppsala, Sweden
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Abstract |
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Key Words: chromatic ocular disposition color vision ultraviolet opsin
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Introduction |
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Compared with humans, birds have an additional color channel located in the ultraviolet (UV) to near ultraviolet range. The UV waveband is unperceivable by humans, but it has been shown to be ecologically important to birds. Experimental alterations of the UV component in the plumage have significantly affected sexual signals in many bird species (Maier and Bowmaker 1993; Bennett et al. 1996, 1997; Andersson and Amundsen 1997; Hunt et al. 1997, 1998, 1999), and it has been demonstrated a number of times that UV plays an important role in prey detection and foraging (Goldsmith 1980; Viitala et al. 1995; Church et al. 1998; Siitari, Honkavaara, and Viitala 1999). Still, UV does not seem to be more important to birds than does other parts of the spectrum (Hunt et al. 2001; Maddocks, Church, and Cuthill 2001). The focus on UV as a separate communication channel that has imbued behavioral studies in recent years ignores potentially important differences in color perception arising from tetrachromacy.
An important step towards an understanding of how animals perceive color is knowledge of their chromatic ocular disposition (COD), meaning the composite effect of the cone visual pigments' (opsin's) wavelength of maximum absorbance (-max), the filtering by the ocular media (including lens and cornea) and the oil droplets of the cones, and the relative abundance of different cone types. There appears to be two main CODs in birds. The most pronounced difference is in the
-max of the opsin in the UV/violet (SWS1) and short-wavelength sensitive (SWS2) cones. One large group (violet sensitive, or VS [Hart et al. 2000b]) possesses SWS1 cones with a
-max ranging from 403 to 426 nm (Hart, Partridge, and Cuthill 1999). A systematically more restricted group (ultraviolet sensitive, or UVS [Hart et al. 2000b]) has a more UV-biased SWS1 with a
-max between 355 and 380 nm (Hart, Partridge, and Cuthill 1999). The VS system has been demonstrated throughout the avian phylogeny, in Anas platyrhyncos (Jane and Bowmaker 1988), Gallus gallus (Bowmaker et al. 1997), Spheniscus humboltii (Bowmaker and Martin 1985), Coturnix coturnix japonica (Bowmaker et al. 1993), Meleagris gallopavo (Hart, Partridge, and Cuthill 1999), Pavo cristatus (Hart 1998), Puffinus puffinus (Bowmaker et al. 1997), Struthio camelus (Wright and Bowmaker 2001), and Taeniopygia guttata (Bowmaker et al. 1997). The UVS system has so far been found only in birds of the orders Passeriformes and Psittaciformes: Leiotrix lutea (Maier and Bowmaker 1993), Melopsittacus undulatus (Bowmaker et al. 1997), Sturnus vulgaris (Hart, Partridge, and Cuthill 1998), Serinus canaria (Das et al. 1999), Parus caeruleus (blue tit) (Hart et al. 2000b), Turdus merula (Hart et al. 2000b) and four species of estrildid finches (Hart et al. 2000a) (for common names, see table 1).
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Microspectrophotometry (MSP) has been the standard method used to examine the COD of animals. To prepare retinas for MSP, the live subjects are held in darkness for several hours before being sacrificed and having their eyes dissected (Hart, Partridge, and Cuthill 1999). Due to the complexity of the method, the absorbance of visual pigments has only been examined in a limited number of species. From in vitro examination, Wilkie et al. (2000) was able to determine the shift in -max that results from typical between-species amino acid substitutions in five spectral tuning sites in the SWS1 amino acid sequence. Shi, Radlwimmer, and Yokoyama (2001) identified five additional tuning sites in a study on mammals. Of all amino acid changes identified, those in positions 86, 90, and 93 (following the amino acid numbering of bovine rhodopsin) are of particular importance to the spectral tuning in birds (Shi, Radlwimmer, and Yokoyama 2001). Substitutions in four of the sites described by Wilkie et al. (2000) lead to minor or no shifts in
-max (A86S: -1 nm; T93V: +3; A118T: +3; S298A: 0), but a change from cysteine (C) to serine (S) in position 90 leads to a substantial change in
-max (35 nm). Hence a C in position 90 characterizes the UVS group, whereas the VS group has an S in the same position (Yokoyama, Radlwimmer, and Blow 2000). Based on Wilkie et al. (2000) we have developed a molecular method that can be used to quickly, easily, and cheaply assess the approximate COD in almost any bird by sequencing part of the SWS1 opsin from small samples of total DNA.
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Materials and Methods |
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Combining the forward primers SU149a, SU161a, and SU193a with the reverse primer SU306b, we conducted PCR on an Eppendorf Mastercycler Gradient. Each 25 µl reaction volume contained 30 to 50 ng total DNA extracts, 0.125 µl 5 U Taq-polymerase (Applied Biosystems), 2.5 µl 10X reaction buffer, 10 pmol of each primer, 0.2 mM of each dNTP, and 50 mM MgCl2. Reaction conditions were 90 s at 94°C, 5x(30 s at 94°C, 30 s at 54°C and, 1 s at 72°C), 38x(15 s at 94°C, 30 s at 54°C, and 5 s at 72°C), and 10 min at 72°C. The extension time was kept very short to minimize nonspecific amplification of longer fragments.
We performed double-stranded sequencing of the PCR product with Big-Dye Terminator Cycle Sequencing v2.0 kit on an ABI-prism 310 automated sequencer following the user's manual. The same primers were used in cycle sequencing as in the PCR. PCR products for sequencing were prepared using Microcon YM-100 and YM-50 centrifugal filter devices (MILLIPORE). In case of amplification of multiple products, we purified the product from a 2% agarose gel using QIAquick Gel Purification kit (QIAGEN).
To translate our sequences we used the published amino acid sequence from Melopsittacus undulatus UV-sensitive opsin (Wilkie et al. 1998) as a template. From the alignment of amino acid sequences, we identified the spectral tuning sites 86, 90, and 93 (Wilkie et al. 2000) and calculated -max values from the tuning sites following Wilkie et al. (2000). We assumed the effect of these sites on spectral tuning to be additive. Although this assumption disregards interactions between sites (see Shi, Radlwimmer, and Yokoyama 2001), additition should provide a reasonable approximation of
-max.
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Results |
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We found five new mutations at position 86 and one at 93, that is, mutations not described in Wilkie et al. (2000). However, since these positions only marginally contribute to the spectral tuning with their previously reported amino acids (Wilkie et al. 2000), we do not expect the new mutations to have any drastic effects on the spectral tuning of the SWS1-opsin. Nevertheless, these new findings call for further investigations using in vitro studies or MSP examination.
Our results confirm that the UV-tuned COD is present in passeriform and psittaciform birds and that most other bird taxa are violet-tuned. However, we found UVS also in the Laridae (genus Larus) and Rheidae families of the orders Ciconiiformes and Struthioniformes, respectively, and VS in the passeriform families Corvidae, Trogonidae, and Tyrannidae, as well as in the Struthioniform family Struthionidae.
For unknown reasons, we failed to amplify the SWS1 opsin sequence from the following species: Branta bernicla (brant), Anas crecca (green-winged teal), Apus apus (common swift), Aquila chrysaetos (golden eagle), Podiceps cristatus (great crested grebe), Mommotus mommota (blue-crowned motmot) and Strix aluco (tawny owl).
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Discussion |
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The distribution of the UVS/VS character in the avian phylogeny has been considered to reflect the degree of relatedness of avian taxa and to be most parsimoniously explained by a single evolutionary split of the passeriform and psittaciform lineages from the anseriform and galliform lineages (Hart et al. 2000a). However, that UVS is present in at least nine families from four orders (table 1), interdispersed with VS taxa (fig. 1) strongly indicates that the UVS character has been acquired independently in each of these groups and that its distribution does not reflect the degree of relatedness between avian species. The vast majority of vertebrate animals studied have the amino acid serine in position 90, and this has lead Yokoyama, Radlwimmer, and Blow (2000) to suggest that having cystein in the same position is a derived state in birds. Indeed, the exclusive presence of serine in position 90 in the majority of families examined suggests that VS is the primitive state. This is also indicated by molecular and morphological phylogenies (fig. 1). However, the closest relatives to birds in which the SWS1 opsin is known are chameleon and mammals (Yokoyama, Radlwimmer, and Blow 2000), and these taxa are probably too distant relatives to provide phylogenetic resolution, as this character state varies even within avian families. Furthermore, the character state (UVS/VS) is controlled by a single-nucleotide mutation (Wilkie et al. 2000). One should therefore be careful not to draw too far-reaching conclusions from the character state in any extant outgroup. The closest living relatives to birds are the crocodilians, with which they share a common ancestor no younger than 250 Myr (Benton 1997). This provides ample time for multiple character changes.
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An animal's response to a color signal depends on the signal's fit on the COD of that particular species, rather than what properties a human observer considers the signal to have. Evolutionary biologists and behavioral ecologists need to acknowledge the COD of their study animal to ask relevant questions and design experiments correctly. Indeed, the distribution of CODs is such a complex one that, when studying animal signaling, it may be necessary to verify the CODs even if they are known from related species. In bird studies, our method offers a considerably more practical tool for that purpose than does MSP. However, we do not imply that our method should replace the latter; MSP is undeniably more direct and informative. It is worth noting that some species carrying the SWS1 opsin gene might not express it, posses a very low proportion of SWS1 cones in the retina, or have ocular media absorbing ultraviolet light. So far, all our results are in agreement with those from MSP, although our -max approximations deviate by up to 15 nm, supporting a fine-tuning role for other sites (see Shi, Radlwimmer, and Yokoyama 2001). Our method can be used to quickly estimate a COD from total DNA, without the need to keep or sacrifice the animal. It thereby facilitates large screenings, including rare and endangered species, making it possible to find species with an aberrant COD suitable for MSP examination.
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New Sequences |
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Acknowledgements |
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Footnotes |
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E-mail: olle.hastad{at}ebc.uu.se.
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Literature Cited |
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Andersson, S., and T. Amundsen. 1997. Ultraviolet colour vision and ornamentation in bluethroats. Proc. R. Soc. Lond. B Biol. Sci. 264:1587-1591.[CrossRef][ISI]
Bennett, A. T. D., I. C. Cuthill, J. C. Partridge, and K. Lunau. 1997. Ultraviolet plumage colors predict mate preferences in starlings. Proc. Natl. Acad. Sci. USA 94:8618-8621.
Bennett, A. T. D., I. C. Cuthill, J. C. Partridge, and E. J. Maier. 1996. Ultraviolet vision and mate choice in zebra finches. Nature 380:433-435.[CrossRef][ISI]
Benton, M. J. 1997. Vertebrate palaeontology, 2nd edition. Chapman & Hall, London.
Bowmaker, J. K., L. A. Heath, S. E. Wilkie, and D. M. Hunt. 1997. Visual pigments and oil droplets from six classes of photoreceptor in the retinas of birds. Vision Res. 37:2183-2194.[CrossRef][ISI][Medline]
Bowmaker, J. K., J. K. Kovach, A. V. Whitmore, and E. R. Loew. 1993. Visual pigments and oil droplets in genetically manipulated and carotenoid deprived quail: a microspectrophotometric study. Vision Res. 33:571-578.[CrossRef][ISI][Medline]
Bowmaker, J. K., and G. R. Martin. 1985. Visual pigments and oil droplets in the penguin, Spheniscus humboldti. J. Comp. Physiol. [A] 156:71-78.[ISI]
Church, S. C., A. T. D. Bennett, I. C. Cuthill, and J. C. Partridge. 1998. Ultraviolet cues affect the foraging behaviour of blue tits. Proc. R. Soc. Lond. B Biol. Sci. 265:1509-1514.[CrossRef][ISI]
Cracraft, J. 1981. Toward a phylogenetic classification of the recent birds of the world (class Aves). Auk 98:681-714.[ISI]
Das, D., S. E. Wilkie, D. M. Hunt, and J. K. Bowmaker. 1999. Visual pigments and oil droplets in the retina of a passerine bird, the canary Serinus canaria: microspectrophotometry and opsin sequences. Vision Res. 39:2801-2815.[CrossRef][ISI][Medline]
Fleishman, L. J., E. R. Loew, and M. Leal. 1993. Ultraviolet vision in lizards. Nature 365:397.[CrossRef][ISI]
Goldsmith, T. H. 1980. Hummingbirds see near ultraviolet light. Science 207:786-788.[ISI][Medline]
Goldsmith, T. H. 1990. Optimization, constraint, and history in the evolution of eyes. Q. Rev. Biol. 65:281-322.[ISI][Medline]
Hart, N. S. 1998. Avian photoreceptors. Ph.D. thesis. University of Bristol, United Kingdom.
Hart, N. S. 2001. The visual ecology of avian photoreceptors. Prog. Retin. Eye Res. 20:675-703.[CrossRef][ISI][Medline]
Hart, N. S., J. C. Partridge, A. T. D. Bennett, and I. C. Cuthill. 2000a. Visual pigments, cone oil droplets and ocular media in four species of estrildid finch. J. Comp. Physiol. [A] 186:681-694.[CrossRef][ISI][Medline]
Hart, N. S., J. C. Partridge, and I. C. Cuthill. 1998. Visual pigments, oil droplets and cone photoreceptor distribution in the European starling (Sturnus vulgaris). J. Exp. Biol. 201:1433-1446.
Hart, N. S., J. C. Partridge, and I. C. Cuthill. 1999. Visual pigments, cone oil droplets, ocular media and predicted spectral sensitivity in the domestic turkey (Meleagris gallopavo). Vision Res. 39:3321-3328.[CrossRef][ISI][Medline]
Hart, N. S., J. C. Partridge, I. C. Cuthill, and A. T. D. Bennett. 2000b. Visual pigments, oil droplets, ocular media and cone photoreceptor distribution in two species of passerine bird: the blue tit (Parus caeruleus L.) and the blackbird (Turdus merula L.). J. Comp. Physiol. [A] 186:375-387.[CrossRef][ISI][Medline]
Hunt, S., A. T. D. Bennett, I. C. Cuthill, and R. Griffiths. 1998. Blue tits are ultraviolet tits. Proc. R. Soc. Lond. B Biol. Sci. 265:451-455.[CrossRef][ISI]
Hunt, S., I. C. Cuthill, A. T. D. Bennett, S. C. Church, and J. C. Partridge. 2001. Is the ultraviolet waveband a special communication channel in avian mate choice? J. Exp. Biol. 204:2499-2507.[ISI][Medline]
Hunt, S., I. C. Cuthill, A. T. Bennett, and R. Griffiths. 1999. Preferences for ultraviolet partners in the blue tit. Anim. Behav. 58:809-815.[CrossRef][ISI][Medline]
Hunt, S., I. C. Cuthill, J. P. Swaddle, and A. T. D. Bennett. 1997. Ultraviolet vision and band-colour preferences in female zebra finches, Taeniopygia guttata. Anim. Behav. 54:1383-1392.[CrossRef][ISI][Medline]
Jacobs, G. H. 1993. The distribution and nature of colour vision among the mammals. Biol. Rev. Camb. Philos. Soc. 68:413-471.[ISI][Medline]
Jane, S. D., and J. K. Bowmaker. 1988. Tetrachromatic color vision in the duck (Anas platyrhynchos L.): microspectrophotometry of visual pigments and oil droplets. J. Comp. Physiol. [A] 162:225-236.[ISI]
Kawamuro, K., T. Irie, and T. Nakamura. 1997. Filtering effect of cone oil droplets detected in the P-III response spectra of Japanese quail. Vision Res. 37:2829-2834.[CrossRef][ISI][Medline]
Losey, G. S., T. W. Cronin, T. H. Goldsmith, D. Hyde, N. J. Marshall, and W. N. McFarland. 1999. The UV visual world of fishes: a review. J. Fish Biol. 54:921-943.[CrossRef][ISI]
Maddocks, S. A., S. C. Church, and I. C. Cuthill. 2001. The effects of the light environment on prey choice by zebra finches. J. Exp. Biol. 204:2509-2515.[ISI][Medline]
Maier, E. J., and J. K. Bowmaker. 1993. Colour vision in the passeriform bird, Leiothrix lutea: Correlation of visual pigment absorbance and oil droplet transmission with spectral sensitivity. J. Comp. Physiol. 172:295-301.[ISI]
Okano, T., D. Kojima, Y. Fukada, Y. Shichida, and T. Yoshizawa. 1992. Primary structure of chicken cone visual pigments: vertebrate rhodopsins have evolved out of cone visual pigments. Proc. Natl. Acad. Sci. USA 89:5932-5936.[Abstract]
Palacios, A. G., F. J. Varela, R. Srivastava, and T. H. Goldsmith. 1998. Spectral sensitivity of cones in the goldfish, Carassius auratus. Vision Res. 38:2135-2146.[CrossRef][ISI][Medline]
Rice, P., I. Longden, and A. Bleasby. 2000. EMBOSS: the European molecular biology open software suite. Trends Genet. 16:276-277.[CrossRef][ISI][Medline]
Rozen, S., and H. J. Skaletsky. 1998. Primer3. Code available at http://www.genome.wi.mit.edu/genome_software/other/primer3.html.
Shi, Y., F. B. Radlwimmer, and S. Yokoyama. 2001. Molecular genetics and the evolution of ultraviolet vision in vertebrates. Proc. Natl. Acad. Sci. USA 98:11731-11736.
Sibley, C. G., and J. E. Ahlquist. 1990. Phylogeny and classifications of birds: a study in molecular evolution. Yale University Press, New Haven, Conn.
Siitari, H., J. Honkavaara, and J. Viitala. 1999. Ultraviolet reflection of berries attracts foraging birds: a laboratory study with redwings (Turdus iliacus) and bilberries (Vaccinium myrtillus). Proc. R. Soc. Lond. B Biol. Sci. 266:2125-2129.[CrossRef][ISI]
Viitala, J., E. Korpimaki, P. Palokangas, and M. Koivula. 1995. Attraction of kestrels to vole scent marks visible in ultraviolet light. Nature 373:425-427.[CrossRef][ISI]
Wilkie, S. E., P. R. Robinson, T. W. Cronin, S. Poopalasundaram, J. K. Bowmaker, and D. M. Hunt. 2000. Spectral tuning of avian violet- and ultraviolet-sensitive visual pigments. Biochemistry 39:7895-7901.[CrossRef][ISI][Medline]
Wilkie, S. E., P. M. A. M. Vissers, D. Das, W. J. Degrip, J. K. Bowmaker, and D. M. Hunt. 1998. The molecular basis for UV vision in birds: spectral characteristics, cDNA sequence and retinal localization of the UV-sensitive visual pigment of the budgerigar (Melopsittacus undulatus). Biochem. J. 330:541-547.[ISI][Medline]
Wright, M. W., and J. K. Bowmaker. 2001. Retinal photoreceptors of paleognathous birds: the ostrich (Struthio camelus) and rhea (Rhea americana). Vision Res. 41:1-12.[CrossRef][ISI][Medline]
Yokoyama, S., F. B. Radlwimmer, and N. S. Blow. 2000. Ultraviolet pigments in birds evolved from violet pigments by a single amino acid change. Proc. Natl. Acad. Sci. USA 97:7366-7371.