The shortwave-sensitive class I of visual pigments in vertebrates has the widest variation in peak sensibility, ranging from ultraviolet (355-390 nm) to violet (390-440 nm). Phylogenetic evidence indicates that the ancestral pigment was probably UV-sensitive (UVS) and that the shifts between violet and UV have occurred several times throughout vertebrate evolution. These appear to be two major tuning mechanisms present in vertebrates: one in the non-avian vertebrates and one in the avian group. Avian UVS pigments have Cys90 while VS pigments have Ser90. Non-avian UVS pigments have Phe86, which is replaced in VS pigments. The objective of this project has been to extend our understanding of the molecular basis of SWS1 pigment tuning by addressing whether the effect of the residues present at these sites are consistent across different vertebrate orders. Within the mammalian order, it has been possible to elucidate the SWS1 tuning mechanism within the rodent lineage, showing that the VS pigment in the grey squirrel has a different tuning mechanism compared to the guinea pig and that nocturnal flying squirrels have dispensed with colour vision. The visual system of the platypus, a montreme from the bases of the mammalian radiation has also been investigated and shown to have retained colour vision by a different route from all other mammals. An analysis of the tuning mechanism of primate VS pigments has shown that violet-sensitivity was achieved though a unique mechanism. In the avian order the results have shown that the ancestral avian pigment became VS through a Ser86 substitution and only later did extant bird species utilize site 90 to re-create UV sensitivity. The presence of UVS pigments has also been investigated in long-lived parrot species; partial sequences have revealed that all species possess Cys90, indicating the presence of a UVS pigment in fifteen species of parrots.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:505503 |
| Date | January 2009 |
| Creators | Carvalho, Livia dos Santos |
| Publisher | University College London (University of London) |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://discovery.ucl.ac.uk/17269/ |
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