Carotenoids and life-history evolution in animals.

Animals must allocate finite resources amongst competing demands. A suite of such trade-offs is thought to occur in the deployment of carotenoids, being widely responsible for sexual coloration and also important in antioxidant and immune defences. Experimental manipulation of dietary carotenoid availability is a useful approach for elucidating the mechanistic bases of carotenoid allocation trade-offs. Recent work using birds has shown that both sexual display and immune defences can be limited by carotenoid availability, providing support for the hypothesis that males allocating greater amounts of carotenoids to sexual coloration are advertising their superior health. Carotenoid availability has also been shown to limit egg-laying capacity in birds, although it remains to be seen whether carotenoid display in females advertises reproductive potential. More experiments are required to ascertain the importance of direct (material) and indirect (genetic) benefits accruing through choosing to mate with individuals that have greater carotenoid display.