Dietary carotenoids mediate a trade-off between egg quantity and quality in Japanese quail

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Carotenoids offer animals many nutritional, health, and reproductive benefits. When in high supply, carotenoids can boost antioxidant protection and immune strength as well as stimulate egg production and enrich the color of sexual ornaments like feathers. Certain reproductive investments, however, often come at the cost of others; for example, the production of many offspring may compromise the quality of those offspring. Under such a scenario, we rarely know the precise intrinsic or extrinsic mechanism that generates such a reproductive trade-off. Here I show that variation in dietary carotenoid intake mediates a trade-off between egg quantity and quality in female Japanese quail (Coturnix japonica). Females fed high doses of two common plant carotenoids, lutein and zeaxanthin, during a 1-month diet experiment were more likely to lay eggs, but produced eggs with significantly smaller yolks. Yolk serves as the critical nutritional supply for developing embryos, and several studies show dramatic negative developmental consequences for offspring that are allocated scant yolk reserves. These results demonstrate nutritional control of yolk size and highlight a potential reproductive cost of high carotenoid accumulation in multiparous birds. In future studies, we should consider total yolk-carotenoid reserves rather than simply carotenoid concentration to better understand the cost-benefit balance of these nutrients.