Animal allure and health linked by plant pigments.

Darwin introduced the idea that ornamental secondary sexual traits have evolved in response to female preferences for showy males. Among such traits, yellow and red carotenoid-based ornaments have been considered as particularly good candidates for explaining why and how females would benefit from mating with showy partners. Because carotenoids can be used for promotion of both health and appearance, colourful male ornaments should honestly reveal the vigour of the bearers. Two recent experiments with birds now show how allocation of bodily carotenoids to sexual signalling is traded off against the use of carotenoids for boosting immune function. Copyright 2003 Wiley Periodicals, Inc.