Carotenoid-based sexual coloration and body condition in nesting male sticklebacks

The extent, corrected for body size, and intensity of nuptial coloration of breeding male three-spined sticklebacks Gasterosteus aculeatus L. from a S cottish freshwater population were highly variable but correlated, both in the field and after a period of nest-building in the laboratory. However, m arked changes in coloration occurred between the field and the laboratory s creenings and the coefficients of variation amongst males decreased. In gen eral, intensity of coloration increased between the field and laboratory sc reenings, but changes in size-corrected extent were not consistently direct ional. For both Indices, there was a negative relationship between the fiel d value and amount by which colour changed between sampling sessions, with fish that were initially the dullest gaining most in colour. Size-corrected extent and (in particular) intensity of coloration in the field sample wer e associated positively with body condition measured post mortem and there was a negative, though non-significant, relationship between the extent of coloration and the proportion of white cells in the blood. No such associat ions were found for the laboratory colour screening. The concentration of a staxanthin in the lower jaw was related strongly and positively to both siz e-corrected extent and intensity of coloration at the laboratory screening and related negatively, though non-significantly, to proportional white cel l counts. These data have implications both for the interpretation of previ ous laboratory studies and for the design of future experiments, and sugges t that coloration is only a true indicator of male quality when measured in the field. (C) 2000 The Fisheries Society of the British Isles.