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

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The extent, corrected for body size, and intensity of nuptial coloration of breeding male three‐spined sticklebacksGasterosteus aculeatusL. from a Scottish freshwater population were highly variable but correlated, both in the field and after a period of nest‐building in the laboratory. However, marked changes in coloration occurred between the field and the laboratory screenings and the coefficients of variation amongst males decreased. In general, intensity of coloration increased between the field and laboratory screenings, but changes in size‐corrected extent were not consistently directional. For both indices, there was a negative relationship between the field 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 were 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 associations were found for the laboratory colour screening. The concentration of astaxanthin in the lower jaw was related strongly and positively to both size‐corrected extent and intensity of coloration at the laboratory screening and related negatively, though non‐significantly, to proportional white cell counts. These data have implications both for the interpretation of previous laboratory studies and for the design of future experiments, and suggest that coloration is only a true indicator of male quality when measured in the field.