The vitamin A-redox hypothesis: a biochemical basis for honest signaling via carotenoid pigmentation.
Trade-offs in resource allocation have been widely stated as the means by which the honesty of ornamental traits is maintained, but an alternative to this resource trade-off hypothesis is that production of ornamentation is linked to the biochemical efficiency of vital cellular processes. Carotenoids are antioxidants, potentially tying carotenoid-based coloration to the oxidative state of an organism, and some carotenoids are also precursors for vitamin A, which regulates numerous cellular processes. We present a biochemical model for regulation of ornamental coloration based on interdependencies of carotenoid and retinoid biochemistry. We propose that vitamin A regulatory mechanisms, redox systems, and carotenoid pigmentation pathways link carotenoid coloration to oxidative state and to a host of important aspects of performance, such as immune function. The activity of β-carotene ketolase, which catalyzes the oxidation of yellow carotenoids into red carotenoids, is responsive to the states of vitamin A pools and redox systems such that coloration is a direct reflection of the physiological state of an animal. According to the vitamin A-redox hypothesis, feather coloration is associated with a range of performance measures because performance emerges from functionality of the same basic cellular processes that regulate pigmentation. We present the vitamin A-redox hypothesis as a testable alternative hypothesis to the resource trade-off hypothesis for the maintenance of honesty of carotenoid pigmentation.
Department of Biological Sciences, Auburn University, Auburn, Alabama 36849, USA. ghill@auburn.edu
Geoffrey E
GE
Hill
James D
JD
Johnson
D000818:Animals; D005241:Feathers / Q000378:metabolism; D046369:Finches / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D008954:Models, Biological; D010084:Oxidation-Reduction; D010105:Oxygenases / Q000378:metabolism; D010858:Pigmentation / Q000502:physiology*; D015398:Signal Transduction; D014801:Vitamin A / Q000378:metabolism*
D014801:Vitamin A; D010105:Oxygenases; C093259:beta-carotene ketolase