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Visual pigments in a living fossil, the Australian lungfish Neoceratodus forsteri.

Bailes HJ, Davies WL, Trezise AE, Collin SP - BMC Evol. Biol. (2007)

Bottom Line: Here we identify and characterise five visual pigments (rh1, rh2, lws, sws1 and sws2) expressed in the retina of N. forsteri.Phylogenetic analysis of the molecular evolution of lungfish and other vertebrate visual pigment genes indicates a closer relationship between lungfish and amphibian pigments than to pigments in teleost fishes.However, the relationship between lungfish, the coelacanth and tetrapods could not be absolutely determined from opsin phylogeny, supporting an unresolved trichotomy between the three groups.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Biomedical Sciences, University of Queensland, St Lucia, Brisbane, QLD 4072, Australia. helena.bailes@manchester.ac.uk

ABSTRACT

Background: One of the greatest challenges facing the early land vertebrates was the need to effectively interpret a terrestrial environment. Interpretation was based on ocular adaptations evolved for an aquatic environment millions of years earlier. The Australian lungfish Neoceratodus forsteri is thought to be the closest living relative to the first terrestrial vertebrate, and yet nothing is known about the visual pigments present in lungfish or the early tetrapods.

Results: Here we identify and characterise five visual pigments (rh1, rh2, lws, sws1 and sws2) expressed in the retina of N. forsteri. Phylogenetic analysis of the molecular evolution of lungfish and other vertebrate visual pigment genes indicates a closer relationship between lungfish and amphibian pigments than to pigments in teleost fishes. However, the relationship between lungfish, the coelacanth and tetrapods could not be absolutely determined from opsin phylogeny, supporting an unresolved trichotomy between the three groups.

Conclusion: The presence of four cone pigments in Australian lungfish suggests that the earliest tetrapods would have had a colorful view of their terrestrial environment.

Show MeSH
The phylogenetic relationships between the vertebrate visual opsin lineages. A series of four duplication events produced the lws, sws1, sws2 and then rh1 and rh2 genes. The position of each branch on the spectrum portrays the approximate spectral sensitivity of each opsin group. Maximum absorbance value ranges (nm) are based on pigments reconstructed with 11-cis retinal. Values are taken from [45], figure adapted from [3].
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Figure 1: The phylogenetic relationships between the vertebrate visual opsin lineages. A series of four duplication events produced the lws, sws1, sws2 and then rh1 and rh2 genes. The position of each branch on the spectrum portrays the approximate spectral sensitivity of each opsin group. Maximum absorbance value ranges (nm) are based on pigments reconstructed with 11-cis retinal. Values are taken from [45], figure adapted from [3].

Mentions: Vertebrate vision in both bright-light (photopic) and dim-light (scotopic) conditions occurs following the absorbance of light by a chromophore (based on either vitamin A1 or A2) attached to a visual pigment protein (opsin) within retinal photoreceptor cells (rods or cones). Opsin proteins are a subgroup of G-protein coupled receptors (GPCRs) with a seven transmembrane domain spanning the photoreceptor outer segment membrane. Changes in amino acids surrounding the binding pocket of the light-sensitive chromophore of the opsin can directly alter the spectral sensitivity of the visual pigment. Opsins arise from paralogous opsin genes, and the resulting visual pigments maximally absorb light from different parts of the spectrum from UV to near infrared (Fig. 1). Species from most vertebrate classes possess one or more of a total of five opsin genes; rh1 (medium wavelength-sensitive 1; found in rods), rh2 (medium wavelength-sensitive 2; found in cones), lws (long wavelength-sensitive; found in cones), sws1 (UV/violet or short wavelength-sensitive 1; found in cones), and sws2 (blue or short wavelength-sensitive 2; found in cones). The persistence, loss or duplication of these opsin genes reflects the spectral environment and visual needs of a species [1-3]. While the opsin complement has been well studied in a number of aquatic and terrestrial species [4-7], there remain large gaps in our understanding of the evolution of vertebrate opsins, particularly among species representing the period prior to the transition onto land such as the sarcopterygian, or lobe-finned fish.


Visual pigments in a living fossil, the Australian lungfish Neoceratodus forsteri.

Bailes HJ, Davies WL, Trezise AE, Collin SP - BMC Evol. Biol. (2007)

The phylogenetic relationships between the vertebrate visual opsin lineages. A series of four duplication events produced the lws, sws1, sws2 and then rh1 and rh2 genes. The position of each branch on the spectrum portrays the approximate spectral sensitivity of each opsin group. Maximum absorbance value ranges (nm) are based on pigments reconstructed with 11-cis retinal. Values are taken from [45], figure adapted from [3].
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2194722&req=5

Figure 1: The phylogenetic relationships between the vertebrate visual opsin lineages. A series of four duplication events produced the lws, sws1, sws2 and then rh1 and rh2 genes. The position of each branch on the spectrum portrays the approximate spectral sensitivity of each opsin group. Maximum absorbance value ranges (nm) are based on pigments reconstructed with 11-cis retinal. Values are taken from [45], figure adapted from [3].
Mentions: Vertebrate vision in both bright-light (photopic) and dim-light (scotopic) conditions occurs following the absorbance of light by a chromophore (based on either vitamin A1 or A2) attached to a visual pigment protein (opsin) within retinal photoreceptor cells (rods or cones). Opsin proteins are a subgroup of G-protein coupled receptors (GPCRs) with a seven transmembrane domain spanning the photoreceptor outer segment membrane. Changes in amino acids surrounding the binding pocket of the light-sensitive chromophore of the opsin can directly alter the spectral sensitivity of the visual pigment. Opsins arise from paralogous opsin genes, and the resulting visual pigments maximally absorb light from different parts of the spectrum from UV to near infrared (Fig. 1). Species from most vertebrate classes possess one or more of a total of five opsin genes; rh1 (medium wavelength-sensitive 1; found in rods), rh2 (medium wavelength-sensitive 2; found in cones), lws (long wavelength-sensitive; found in cones), sws1 (UV/violet or short wavelength-sensitive 1; found in cones), and sws2 (blue or short wavelength-sensitive 2; found in cones). The persistence, loss or duplication of these opsin genes reflects the spectral environment and visual needs of a species [1-3]. While the opsin complement has been well studied in a number of aquatic and terrestrial species [4-7], there remain large gaps in our understanding of the evolution of vertebrate opsins, particularly among species representing the period prior to the transition onto land such as the sarcopterygian, or lobe-finned fish.

Bottom Line: Here we identify and characterise five visual pigments (rh1, rh2, lws, sws1 and sws2) expressed in the retina of N. forsteri.Phylogenetic analysis of the molecular evolution of lungfish and other vertebrate visual pigment genes indicates a closer relationship between lungfish and amphibian pigments than to pigments in teleost fishes.However, the relationship between lungfish, the coelacanth and tetrapods could not be absolutely determined from opsin phylogeny, supporting an unresolved trichotomy between the three groups.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Biomedical Sciences, University of Queensland, St Lucia, Brisbane, QLD 4072, Australia. helena.bailes@manchester.ac.uk

ABSTRACT

Background: One of the greatest challenges facing the early land vertebrates was the need to effectively interpret a terrestrial environment. Interpretation was based on ocular adaptations evolved for an aquatic environment millions of years earlier. The Australian lungfish Neoceratodus forsteri is thought to be the closest living relative to the first terrestrial vertebrate, and yet nothing is known about the visual pigments present in lungfish or the early tetrapods.

Results: Here we identify and characterise five visual pigments (rh1, rh2, lws, sws1 and sws2) expressed in the retina of N. forsteri. Phylogenetic analysis of the molecular evolution of lungfish and other vertebrate visual pigment genes indicates a closer relationship between lungfish and amphibian pigments than to pigments in teleost fishes. However, the relationship between lungfish, the coelacanth and tetrapods could not be absolutely determined from opsin phylogeny, supporting an unresolved trichotomy between the three groups.

Conclusion: The presence of four cone pigments in Australian lungfish suggests that the earliest tetrapods would have had a colorful view of their terrestrial environment.

Show MeSH