Do male two-spotted gobies prefer large fecund females?

A male mating preference for large females may be expected when female size is correlated with fecundity. We tested for such a preference in a fish, the two-spotted goby (Gobiusculus flavescens, Gobiidae), for which a male preference for colorful females has been demonstrated. We offered males a choice between two stimulus females of different size, controlling for female color and stage of egg maturation. We also analyzed the relationship between size and fecundity (total number of eggs in the clutch) by allowing females of different size to spawn in a controlled environment. Female length explained 37% of the variation in fecundity, but males showed only a weak preference for large females. We compared the coefficient of variation (CV) in fecundity between female two-spotted gobies and other fish species for which male preferences for large females have been reported. The CV in fecundity in the two-spotted goby was among the lowest. We suggest that the low variation limits the potential fecundity benefit to be gained by a male selecting females on the basis of size alone. Our study emphasizes the importance of the variation in partner quality for the direction and the strength of mate preferences, as suggested by theoretical models.