Behavioral Ecology Advance Access published online on April 15, 2008
Behavioral Ecology, doi:10.1093/beheco/arm152
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Experimental support for the makeup hypothesis in nestling tawny owls (Strix aluco)
a Department of Ecology and Evolution, Biophore, University of Lausanne, 1015 Lausanne, Switzerland b Division of Environmental and Evolutionary Biology, IBLS, Graham Kerr Building, Glasgow University, Glasgow G12 8QQ, UK c School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA
Address correspondence to R. Piault. E-mail: romain.piault{at}unil.ch.
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Abstract |
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Body condition can affect coloration of traits used in sexual selection and parent–offspring communication by inducing rapid internal changes in pigment concentration or aggregation, thickness of collagen arrays, or blood flux. The recent "makeup hypothesis" proposes an alternative honesty-reinforcing mechanism, with behaviorally mediated deposition of substances on body surfaces ("cosmetics") generating covariation between body condition and coloration. In birds, the uropygial gland wax is actively spread on feathers using the bill and changes in its deposition rate may cause rapid changes in bill and plumage coloration. Using tawny owl nestlings, we tested 3 predictions of the makeup hypothesis, namely that 1) quantity of preen wax deposited accounts for variation in bill coloration, 2) an immune stimulation (induced by injection of a lipopolysaccharide [LPS]) impairs uropygial gland wax production, and 3) different intensities of immune stimulations (strong vs. weak stimulations induced by injections of either LPS or phytohemagglutinin [PHA], respectively) and high versus low food availabilities result in different bill colorations. We found that 1) preen wax reduced bill brightness, 2) a challenge with LPS impaired uropygial gland development, and 3) nestlings challenged with LPS had a brighter bill than PHA-injected nestlings, whereas diet manipulation had no significant effect. Altogether, these results suggest that a strong immune challenge may decrease preen wax deposition rate on the bill of nestling birds, at least by impairing gland wax production, which causes a change in bill coloration. Our study therefore highlights that cosmetic colors might signal short-term variation in immunological status.
Key words: bill coloration, immune status, makeup hypothesis, preening behavior, preen wax, uropygial gland.
Received 7 June 2007; revised 16 November 2007; accepted 6 December 2007.