Evol Ecol Res 7: 251-262 (2005) Full PDF if your library subscribes.
Sex differences in carotenoid status and immune performance in zebra finches
Kevin J. McGraw1* and Daniel R. Ardia2‡
1Department of Neurobiology and Behavior and 2Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY 14853, USA
Address all correspondence to Kevin McGraw, School of Life Sciences, Arizona State University, Tempe, AZ 85287-4501, USA.
Sex differences in immunity are common throughout the animal kingdom, with males typically showing reduced immune capacity compared with females due to the immunosuppressive action of androgens like testosterone. However, in animals (e.g. birds, fishes) in which immunostimulatory carotenoid pigments are used to develop colourful traits, males tend to circulate higher concentrations of these immunomodulators to become more colourful than females. In these instances, it is uncertain how differences in carotenoid status might affect sex-specific patterns of immune function. We tested the relationship between carotenoid status and two measures of immunocompetence in male and female zebra finches (Taeniopygia guttata). Non-breeding males circulated a higher concentration of carotenoids through blood than females. Females mounted a significantly higher cell-mediated immune response (to phytohaemagglutinin) than males, but males mounted a significantly higher humoral response (to sheep red blood cells) than females. When supplemented with dietary carotenoids, males showed significant improvements in both cell-mediated and humoral immune performance, while females only showed elevated humoral responsiveness. These results generally support the immunostimulatory role of carotenoids in colourful male and female birds, and indicate that males may gain certain offsetting, carotenoid-facilitated immunological benefits relative to females. It appears that shunting carotenoids to the humoral arm of the immune system – perhaps a more costly yet more effective means of fighting off pathogens – may take priority over elevating cell-mediated immunity in both sexes.
Keywords: carotenoids, immunocompetence, sex differences in immunity, sexual selection, Taeniopygia guttata.
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