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

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.

Phylogeography and genetic structuring of European nine-spined sticklebacks (Pungitius pungitius)-mitochondrial DNA evidence.

As a consequence of colonisation from different glacial refugia, many northern European taxa are split into distinct western and eastern lineages. However, as for the nine-spined stickleback (Pungitius pungitius), the exact location of the contact zone between lineages often remains poorly known. We assessed the genetic differentiation and diversity in the nine-spined stickleback within Europe using 1037 base pairs of cytochrome b sequence for 320 individuals from 57 locations, including pond, lake, river, and coastal habitats. Our main aims were (i) to locate the contact zone between the previously recognized western and eastern lineages, (ii) investigate latitudinal patterns in genetic diversity, (iii) compare genetic diversity among different habitat types, and (iv) date the known split between eastern and western lineages. The data revealed the split between eastern and western to be located across the Danish Straits and roughly following the Norway/Sweden border to the North. Reference sites from Canada form their own clades, and one of the Canadian sites was found to have a haplotype common to the Eastern European lineage, possibly representing an ancestral polymorphism. The split between the two European clades was dated to approximately 1.48 million years ago (Mya), and between Canada and Europe to approximately 1.62 Mya. After controlling for habitat effects, nucleotide (but not haplotype) diversity across populations decreased with increasing latitude. Coastal populations showed significantly higher haplotype diversity (but not nucleotide diversity) than pond populations, but there were no detectable differences in haplotype diversity among different freshwater habitat types (viz. river, lake and pond populations), or between coastal and lake/river populations. Sequences were found to cluster according to their geographic proximity, rather than by habitat type, and all habitat types were found within each major clade, implying that colonisation and adaptation between the coastal and freshwater environments in different regions must have occurred in parallel.