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J.W. L. Parry, A. Carboo, J.K. Bowmaker, O. Seehausen, K.L. Carleton; SPECTRAL SENSITIVITY TUNING BY DIFFERENTIAL GENE EXPRESSION IN AFRICAN CICHLIDS . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3633.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: The African great lakes contain species flocks of cichlids that are thought to be in the process of divergent evolution and have adapted to a range of ecological niches. We have examined the visual pigments of 3 genera of Malawi cichlids from different photic habitats and 5 species of a single genus that occupy different habitats within lake Victoria. Methods: Retinal samples from several individuals of each species were examined by MSP. Tissue was preserved for genetic analysis. Results: Pundamilia spp. from Victoria all had pigments with identical λmax: single cones at 455 nm and double cone constituents at 528 nm and 564 nm. Two species possessed only 528/564–nm double cones, whereas the other 3 had in addition, 564–nm identical double cones. In contrast, the Malawi species had a complement of 7 cone pigments. Pseudotropheus acei had 482/535–nm double cones and 379–nm single cones with small populations of 506–nm single cones and 506/535–nm doubles. In addition, individual single cones had λmax at 415, 455 and 555 nm. Melanochromis vermivorus had a similar arrangement of double cones, but 418–nm single cones. In contrast, Lethrinops intermedius possessed longer–wave 532/569 double cones and 455 single cones with a small population of 532–nm single cones. Conclusions: Carleton & Kocher (2001, Mol. Biol. Evol. 18:1540–50) using real–time PCR, suggested that Malawi cichlids use differential gene expression to tune their differing spectral sensitivities. They have the potential to express cone pigments with λmax at 370, 450, 490, 535 and 570 nm, suggested products of SWS1, SWS2A, SWS2B, RH2 and LWS genes respectively, but exhibit only three of these in any given species. Our data support this hypothesis, with the rare additional pigments implying leaky expression of the other genes. However, the 418–nm and 505–nm pigments reported here require additional opsins. In contrast, the Victorian cichlids all have the same pigment complement, but adapt to their various photic environments by differential expression of the same genes in different pairings within double cones.
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