Traits that influence social interactions (signals) are widely thought to be honest indicators of some underlying quality of their bearer. One hypothesis is that a signal and the bearer's immunocompetence are linked via a condition-dependent pathway. We tested this idea by measuring the effect of specific dietary components on the development of a melanin-based plumage signal and the production of antibodies in juvenile male house sparrows entering their first moult. We maintained sparrows on one of three artificial diets: high total protein, low total protein, or intermediate protein with the precursors of melanin, phenylalanine and tyrosine (PT), reduced by 50%. Diet did not affect survival or weight gain. Two aspects of male plumage differed between treatments; the white wing bar was significantly smaller in low-protein males, and the black bib feathers had significantly higher reflectance in PT-reduced males. PT reductions had no effect on bib size. PT-reduced birds also produced more antibodies to diphtheria and tetanus antigens than did other subjects. After repeating the experiment using a better control and a different diet formula to compensate for an energy imbalance resulting from reduced PT levels, PT reduction again produced lighter bib feathers, but the effect of diet on antibody production disappeared. We conclude that the amino acid precursors to melanin affect melanin synthesis if scarce in the diet, but in this case, do not affect size, the most conspicuously variable aspect of the signal. We found no evidence of a condition-dependent link between melanin synthesis and immunocompetence.
|Number of pages||11|
|State||Published - Nov 2005|
Bibliographical noteFunding Information:
We thank Meg Hatch, Tria Kinnard and Herman Mays for help with maintaining the sparrows. Douglas Sejberg assisted with the ELISA analyses. Funding for this project was provided to D.F.W. by the University of Kentucky and the National Science Foundation (IBN-9816989) and to D.H. by the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (Formas), Carl Tryggers Stiftelse, and Crafoordska Stiftelsen. All aspects of these manipulations were approved by the University of Kentucky Institutional Animal Care and Use Committee (Protocol 97-0006L). The manuscript was improved by comments from Alexandre Roulin and four anonymous referees.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics
- Animal Science and Zoology