title: Spectral tuning by selective chromophore uptake in rods and cones of eight populations of nine-spined stickleback (Pungitius pungitius).
abstract: The visual pigments of rods and cones were studied in eight Fennoscandian populations of nine-spined stickleback (Pungitius pungitius). The wavelength of maximum absorbance of the rod pigment (λ(max)) varied between populations from 504 to 530 nm. Gene sequencing showed that the rod opsins of all populations were identical in amino acid composition, implying that the differences were due to varying proportions of chromophores A1 and A2. Four spectral classes of cones were found (two S-cones, M-cones and L-cones), correlating with the four classes of vertebrate cone pigments. For quantitative estimation of chromophore proportions, we considered mainly rods and M-cones. In four populations, spectra of both photoreceptor types indicated A2 dominance (population mean λ(max)=525-530 nm for rods and 535-544 nm for M-cones). In the four remaining populations, however, rod spectra (mean λ(max)=504-511 nm) indicated strong A1 dominance, whereas M-cone spectra (mean λ(max)=519-534 nm) suggested substantial fractions of A2. Quantitative analysis of spectra by three methods confirmed that rods and cones in these populations use significantly different chromophore proportions. The outcome is a shift of M-cone spectra towards longer wavelengths and a better match to the photic environment (light spectra peaking >560 nm in all the habitats) than would result from the chromophore proportions of the rods. Chromophore content was also observed to vary partly independently in M- and L-cones with potential consequences for colour discrimination. This is the first demonstration that selective processing of chromophore in rods and cones, and in different cone types, may be ecologically relevant.
authors: Department of Biosciences, University of Helsinki, P.O. Box 65, FI-00014 Helsinki, Finland. pia.k.saarinen@helsinki.fi
authors: Pia
authors: P
authors: Saarinen
authors: Johan
authors: J
authors: Pahlberg
authors: Gábor
authors: G
authors: Herczeg
authors: Martta
authors: M
authors: Viljanen
authors: Marika
authors: M
authors: Karjalainen
authors: Takahito
authors: T
authors: Shikano
authors: Juha
authors: J
authors: Merilä
authors: Kristian
authors: K
authors: Donner
mesh_terms: D000042:Absorption; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D004777:Environment; D005387:Finland; D005843:Geography; D008027:Light; D015591:Microspectrophotometry / Q000379:methods*; D008969:Molecular Sequence Data; D025341:Principal Component Analysis; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism* / Q000528:radiation effects; D012168:Retinal Pigments / Q000378:metabolism*; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism* / Q000528:radiation effects; D017299:Rod Opsins / Q000378:metabolism; D017422:Sequence Analysis, DNA; D023701:Smegmamorpha / Q000235:genetics / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D012168:Retinal Pigments; D017299:Rod Opsins