Does female nuptial coloration reflect egg carotenoids and clutch quality in the two-spotted goby (Gobiusculus flavescens, Gobiidae)?

1. Carotenoid based ornamentation has often been suggested to signal mate quality and species with such ornaments have frequently been used in studies of sexual selection. 2. FemaleGobiusculus flavescens(two-spotted goby) develop colourful orange bellies during the breeding season. Belly coloration varies among mature females, and previous work has shown nest holding males to prefer females with more colourful bellies. Since males invest heavily in offspring during incubation, the evolution of this preference can be explained if colourful females provide males with eggs of higher quality. 3. We tested this hypothesis by allowing males to spawn with 'colourful' and 'drab' females and comparing parameters including egg carotenoid concentration, clutch size, hatchability and larval viability between groups. We also investigated relationships between egg carotenoid concentration and clutch quality parameters. 4. Eggs from colourful females had higher concentrations of total carotenoids than eggs from drab females. Colourful females produced slightly larger clutches, but no measure of offspring quality differed between the two groups. Belly coloration quantified in photographs prior to spawning was a good predictor of egg carotenoid concentration, but there were no significant relationships between egg carotenoids and the measures of clutch quality. Females with high levels of egg carotenoids spawned slightly earlier, however, possibly because they were more ready to spawn or because of male mate choice. 5. We found that colourful females provided males with slightly larger clutches and eggs that contained more carotenoids, but despite this, the offspring were not of higher quality. Our results call into question the generality of a causal link between egg carotenoids and offspring quality.