Spectral tuning by selective chromophore uptake in rods and cones of eight populations of nine-spined stickleback (Pungitius pungitius)

Abstract

SUMMARYThe 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 ( 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 Scones, 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  max 525-530nm for rods and 535-544nm for M-cones). In the four remaining populations, however, rod spectra (mean  max 504-511nm) indicated strong A1 dominance, whereas M-cone spectra (mean  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. Supplementary material available online at

Pronounced heritable variation and limited phenotypic plasticity in visual pigments and opsin expression of threespine stickleback photoreceptors

“…Such variation in chromophore use is in line with that found in a related species, the nine-spined stickleback (Pungitus pungitus), where the absorbance of all visual pigments (except S) could be accounted for by chromophore shifts (Saarinen et al, 2012). It therefore appears that, in both stickleback species, chromophore use varies between photoreceptor types and multiple SWS2 opsins may be expressed within the single cone population.…”

Visual pigments of Arctic charr (Salvelinus alpinus (L.)) and whitefish (Coregonus lavaretus (L.)) morphs in subarctic lakes

“…Overall, the sample sizes (numbers of individuals) for determining rod spectra for each condition (e.g. time point) in the present study are typical and sufficient for visual pigment studies (Jokela-Määttä et al, 2007;Saarinen et al, 2012), as suggested also by the relatively small standard deviations.…”

“…The sample sizes for each morph and season are typical or even slightly higher compared to many visual pigment studies (e.g. Jokela-Määttä et al, 2007;Saarinen et al, 2012). We acknowledge that a higher number of samples and sampling times would have been necessary to focus more on cone pigments and potentially reveal more insights to A1:A2 ratio along fish ontogeny.…”

“…within a single generation (e.g. Bridges, 1972;Saarinen et al, 2012). Switching from A1 to A2 shifts absorbance spectra towards longer wavelengths in a predictable manner (Dartnall & Lythgoe, 1965;Hárosi, 1994).…”

“…The wider implications of opsin-or chromophore-based spectral shifts are very different. The former concerns heritable differences in visual capabilities, which may even drive speciation (for a recent example, see Seehausen et al, 2008), whereas chromophore-based shifts confer phenotypic plasticity in response to environmental variation (Dartnall et al, 1961;Bridges, 1972;Saarinen et al, 2012). It is therefore essential to distinguish between these mechanisms for achieving spectral shifts.…”