Is the relation between colour and immune response mediated by nutritional condition in spotless starling nestlings?

• Published in: Animal behaviour 2007-11, Vol.74 (5), p.1139-1145
• Main Authors: Soler, Juan J., Aviles, Jesus M., Cuervo, Jose J., Perez-Contreras, Tomas
• Format: Article
• Language: English
• Subjects: Animal behavior; Animal cognition; Animal ethology; Apus; Biological and medical sciences; Birds; Fundamental and applied biological sciences. Psychology; Hypotheses; Ornithology; parent–offspring communication; PHA; Psychology. Psychoanalysis. Psychiatry; signals of need; spotless starling; Sturnus unicolor; Sturnus vulgaris; T-cell-mediated immune response; UV coloration
• ISSN: 0003-3472; 1095-8282
• DOI: 10.1016/j.anbehav.2006.09.026

The hypothesis that nestling coloration is important for parent–offspring communication, because it influences parental feeding decisions, has received strong experimental support. In European starlings, Sturnus vulgaris, and Alpine swifts, Apus melba, manipulation of ultraviolet reflectance of nestlings' mouth and skin affected the amount of food parents provided, and skin brightness of starling nestlings predicted their T-cell-mediated immune response. Therefore, a link between nestling coloration and immunity, mediated by parental effort, was suggested. We explored this hypothesis by experimentally feeding some spotless starling, Sturnus unicolor, nestlings while leaving others in the same nest as a control. First, we found a significant effect of food supplementation on nestlings' immune response, which is a requirement for the hypothesis. Second, we confirmed in spotless starlings the association between skin brightness and ability to raise an immune response. However, this correlation disappeared when we controlled for between-nest variation. These results suggest that parental feeding preference is not the only factor explaining nestling immunity, and that covariation between mean brood nestling coloration and parental quality, and/or intrinsic (i.e. genetic) quality of nestlings, may explain the association between immunity and coloration of nestlings. Finally, within-nest variation in nestling coloration partially explained immune responses because food supplementation had more effect on nestlings with brighter skin. We discuss these results as possible evidence of nestling coloration partially reflecting intrinsic characteristics that affect both ability to produce efficient immune responses and parental feeding preferences.