Prehistoric colour vision: multiple opsin genes in the ancestral vertebrates
Colin, S.P., Knight, M.A., Davies, W.L., Potter, I.C., Hunt, D.M. and Trezise, A.O. (2003) Prehistoric colour vision: multiple opsin genes in the ancestral vertebrates. In: AMSA2003 Marine Biocomplexity, 9 - 11 July, Brisbane, Australia.
Lampreys are extant survivors of the agnathan (jawless) stage in vertebrate evolution and they, or their close relatives, appeared at least 540MYA. In contrast to northern hemisphere species, the southern hemisphere lamprey Geotria australis possesses three morphologically and physiologically distinct types of photoreceptors i.e. two cones and one rod with wavelengths of maximal absorbance (downstream/upstream) at 610/616nm, 515/515nm and 506/500nm, respectively. To investigate the molecular basis of these multiple photoreceptor types, and the molecular evolution of the vertebrate opsin genes, we cloned full length cDNAs of five opsin genes (LWS, SWS1, SWS2, Rha & Rhb) using reverse transcription PCR from retinal RNA. We confirmed, from genomic DNA, that these five genes are all the retinal opsin genes present in the Geotria australis genome. The phylogeny of the vertebrate opsin gene family was inferred based on a codon-matched nucleotide sequence alignment. We reveal that the three gene duplication events, which gave rise to the long/red (LWS), ultraviolet/violet (SWS1), short/blue (SWS2) and ancestral middle/green/rod (Rh) opsin genes in vertebrates, likely occurred prior to the divergence of the agnathan jawless fishes and the main jawed vertebrate (gnathostomatous) lineages. Although the selection pressures underlying the origins of colour vision are still unknown, the early vertebrates lived in a shallow water environment, where a wide light spectrum could be exploited by the evolution of multiple visual pigments. Such an event would provide the potential for colour discrimination and a significant selective advantage for these early vertebrates.
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|Murdoch Affiliation:||School of Biological Sciences and Biotechnology|
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