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Colour pattern influences behaviour and affects survival of organisms through perception of light reflectance. Spectrophotometric methods used to study colour optimise precision and accuracy of reflectance across wavelengths, while multiband photographs are generally used to assess the complexity of colour patterns. Using standardised photographs of sand lizards (Lacerta agilis), we compare how colours characterised using point measurements (using the photographs, but simulating spectrophotometry) on the skin differ from colours estimated by clustering pixels in the photograph of the lizard's body. By taking photographs in the laboratory and in the field, the experimental design included two 2-way comparisons. We compare point vs. colour clustering characterisation and influence of illumination in the laboratory and in the field. We found that point measurements adequately represented the dominant colour of the lizard. Where colour patterning influenced measurement geometry, image analysis outperformed point measurement with respect to stability between technical replicates on the same animal. The greater colour variation derived from point measurements increased further under controlled laboratory illumination. Both methods revealed lateral colour asymmetry in sand lizards, i.e. that colours subtly differed between left and right flank. We conclude that studies assessing the impact of colour on animal ecology and behaviour should utilise hyperspectral imaging, followed by image analysis that encompasses the whole colour pattern.
Colour traits can be elaborated through sexual selection and have potential to drive reproductive isolation. Male three-spined sticklebacks (Gasterosteus aculeatus) express striking visual signals to attract choosy females during courtship, typically expressed as red carotenoid-based pigmentation on their throat and jaw during the breeding season, along with blue eyes and blue/green flanks. The extent and intensity of red colouration in males have been linked to fitness benefits to females, including body condition, parasite resistance, parental ability and nest defence. In some populations in the Pacific Northwest of North America, male three-spined sticklebacks express melanic nuptial colouration. In these populations, male possess black throats instead of red, and have dark or black bodies. Melanic males are associated with waterbodies that are red-shifted due to the presence of tannins, where the ambient light environment is dominated by long wavelengths. Here we report the first discovery outside North America of melanic populations of threespined sticklebacks on the island of North Uist in the Scottish Hebrides, on the northwest Atlantic coast of Europe. These populations are associated with a hotspot of stickleback morphological diversity and occur in association with red-shifted waterbodies.