title: Do carotenoids buffer testosterone-induced immunosuppression? An experimental test in a colourful songbird.
abstract: Testosterone (T) is hypothesized to be an important honesty reinforcer of animal sexual signals. Owing to its immunosuppressive effects, only those individuals that can immunologically withstand high T levels can develop the most exaggerated traits. To date, few studies have isolated phenotypic or genotypic buffers that provide 'high-quality' animals with such an advantage. Dietary carotenoid pigments may in fact confer such a benefit because when in high supply carotenoids boost immunocompetence and coloration in animals like birds and fishes. We examined the experimental effect of T elevation on carotenoid and immune status in male and female zebra finches (Taeniopygia guttata) and found that T was immunostimulatory in a generalized cell-mediated challenge. We also detected a significant interaction between T treatment and the change in plasma carotenoids that occurred during the immune challenge; the relationship between blood carotenoid change and immunity was positive in controls and negative in T-implanted birds. This suggests that, while correlationally birds with high carotenoid stores were inherently better at mounting strong immune responses, experimentally administered T induced birds to deplete carotenoids for maximizing their health. Our findings highlight a nutrient-specific mechanism by which animals escape high immune costs of T elevation and thus can still elevate ornamentation.
authors.affiliation: Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA. kevin.mcgraw@asu.edu
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: McGraw
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Ardia
mesh_terms: D000818:Animals; D002338:Carotenoids / Q000097:blood*; D004487:Edema / Q000139:chemically induced / Q000276:immunology; D005260:Female; D046369:Finches / Q000276:immunology* / Q000378:metabolism; D007111:Immunity, Cellular / Q000187:drug effects*; D007165:Immunosuppression Therapy; D008297:Male; D010835:Phytohemagglutinins / Q000494:pharmacology; D013739:Testosterone / Q000494:pharmacology*; D014921:Wings, Animal
chemical_list: D010835:Phytohemagglutinins; D002338:Carotenoids; D013739:Testosterone