Association between parasite load and orange, but not blue, male nuptial colouration in Etheostoma caeruleum.

The hypothesis that males possessing more vivid nuptial colouration are of better quality with regard to individual measures of health such as parasite infection was investigated by taking spectral measurements of orange and blue bars in the nuptial males of a sexually dichromatic stream fish rainbow darter Etheostoma caeruleum to determine if male colouration in this species varied with parasite load in the form of black spot disease. The yellow chroma of orange bars, i.e. the relative contribution of wavelengths in the range of 550-625 nm to total brightness, was the only spectral measurement significantly associated with parasite counts. These results are discussed in the context of sexual selection and the potential of orange bars in E. caeruleum to serve as honest indicators of quality to potential mates.