Differential effects of endoparasitism on the expression of carotenoid- and melanin-based ornamental coloration

K. J. McGraw, G. E. Hill

Research output: Contribution to journalArticlepeer-review

255 Scopus citations


The striking diversity of sexual dimorphisms in nature begs the question: Why are there so many signal types? One possibility is that ornamental traits convey different sets of information about the quality of the sender to the receiver. The colourful, pigmented feathers of male birds seem to meet the predictions of this hypothesis. Evidence suggests that carotenoid pigmentation reflects the nutritional condition of males during moult, whereas in many instances melanin pigmentation is a reliable indicator of social status. However, as of yet there have been no experimental tests to determine how these two ornament types respond to the same form of environmental stress. In this study, we tested the effect of endoparasitic infection by intestinal coccidians (Isospora sp.) on the expression of both carotenoid- and melanin-based ornamental coloration in captive male American goldfinches (Carduelis tristis). We found that the carotenoid-based plumage and bill coloration of parasitized males was less saturated than that developed by unparasitized males, but that the brightness and size of melanin-based black caps did not differ between the groups. These findings provide the most robust empirical support to date for the notion that carotenoid and melanin ornaments reveal different information to conspecifics.

Original languageEnglish (US)
Pages (from-to)1525-1531
Number of pages7
JournalProceedings of the Royal Society B: Biological Sciences
Issue number1452
StatePublished - Aug 7 2000
Externally publishedYes


  • American goldfinch
  • Carduelis tristis
  • Coccidia
  • Honest advertisement
  • Isospora
  • Plumage coloration

ASJC Scopus subject areas

  • General Biochemistry, Genetics and Molecular Biology
  • General Immunology and Microbiology
  • General Environmental Science
  • General Agricultural and Biological Sciences


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