NOLAN, P M; JOUVENTIN, P; DOBSON, FS; Arizona State Univ.; CNRS-France; Auburn Univ.: Plumage color predicts immune response in king penguins
Mate choice is particularly important in slow-breeding species, like king penguins (Aptenodytes patagonicus), because a poor choice of mate can not be corrected for a year or more. King penguin males are not territorial, so females are unable to assess a male�s quality based on his territory and therefore must use another cue. Immune strength may be reflected by ornamental bill or feather color, traits that are especially revealing in penguins because the birds have no opportunity to feed during molt. We tested the hypothesis that plumage color in the king penguin reflects an individual�s immunocompetence, by presenting birds with a phytohaemaglutinin (PHA) challenge and measuring the T-cell lymphocyte response 24 hours later. We captured 53 unpaired adult males on Possession Island, in the Crozet Archipelago (46o25�S, 51o45�E), then measured ornamental colors on the upper breast, the auricular patch, and the beak spot. To assess immune strength, we measured footweb thickness before, and 24 hours after, injecting a 500 �l bolus of distilled water containing 500 �g of PHA into the footweb. All males showed a response to the PHA challenge, with a mean (+/- SE) swelling of 2.27 (+/- 0.12) mm, and all color measures showed substantial variation. Only breast hue showed a significant relationship with footweb swelling (rs = -0.33, n = 53, p = 0.015). Breast hue varies from a yellow/orange color (lower hue values) to a rusty brown color (higher hue values), so this result indicates that birds with less-darkly colored breast patches showed the strongest response to challenge with PHA. We conclude that ornamental color does reflect immune strength in the king penguin, although the various ornaments seem to have different signal contents that may represent differences in physiological trade-offs or differences in absorption of the pigment underlying these colors.
