Fecundity compromises attractiveness when pigments are scarce

Theory predicts that the trade-off between ornamentation and fecundity limits female attractiveness. However, there is little evidence on this theoretical trade-off and its proximate background. Our aim was to study whether pigment availability modulates this potential relationship in blue-footed booby females. We supplemented females with dietary carotenoids after laying the first egg and assessed the change in foot color, a carotenoid-based sexually selected trait in both sexes. We measured the change in body mass and in the levels of plasma antioxidants and carotenoids. Also, we registered the mass and volume of eggs. Surprisingly, experimental females reduced zeaxanthin concentration in plasma, but not other carotenoids or total antioxidant levels. Conversely, they increased foot color intensity and laid heavier second eggs and larger second and third eggs than controls. Furthermore, under natural conditions (controls), ornamentation was negatively associated with the mass and volume of second eggs, but the association was reversed under conditions of high carotenoid availability (experimental females). Results suggest that carotenoid availability may mediate the theoretical trade-off between ornamentation and fecundity. We highlight that pigment limitation for females could represent an evolutionary pathway to male choosiness in the blue-footed booby.