Tests of association between the humoral immune response of red-winged blackbirds (Agelaius phoeniceus) and male plumage, testosterone, or reproductive success

David F. Westneat, Dennis Hasselquist, John C. Wingfield

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


We explored the potential relationships between male traits, reproductive success, testosterone levels in the breeding season, and humoral immunocompetence in male red-winged blackbirds (Agelaius phoeniceus). Males responded to a single injection of diphtheriatetanus vaccine by producing antibodies to both antigens. The primary responses to each antigen were positively correlated with each other, but the relationship was clearly non-linear. No male responded strongly to diphtheria without also responding strongly to tetanus, but many males had strong responses to tetanus and weak responses to diphtheria. Response to tetanus was positively associated with hormone levels, whereas the relationship between testosterone and the response to diphtheria was weakly and nonsignificantly negative. We found no convincing relationships between immune responses and male morphological traits (epaulet size, body blackness, and body size), male success in male-male competition (territory size and tenure), or male reproductive success (number of mates, average clutch size, proportion of offspring sired, or proportion of young fledged). These results do not support testosterone acting as a constraint on immunity. Testosterone could be mediating a condition-dependent trade-off between sexual ornaments and the immune system, but the evidence for this was weak, as neither any male sexual trait nor any measure of performance was associated with immune responses. We could not eliminate the possibility that male sexual traits advertise other aspects of immunity that are not dependent upon condition or hormones.

Original languageEnglish
Pages (from-to)315-323
Number of pages9
JournalBehavioral Ecology and Sociobiology
Issue number5
StatePublished - Apr 1 2003

Bibliographical note

Funding Information:
Acknowledgements This project could not have been accomplished without the help of a large number of people both in the field and in the laboratory. We thank the field assistants on this project from all years (1993–1997), particularly Matt Shawkey, Nevelyn Russell, Jessica Brock, Jamie Moseley, and Brian Smith in 1997, and the PCR crew, including Herman Mays, Richard Hanschu, Tamara Roush, Jana Hawks, Nevelyn Russell, Jamie Moseley, and Brent Little. We thank Lynn Erckmann for expert assistance with the steroid assay. This project was supported by funding to D.F.W. from NSF grant IBN9318246, an NSF-Kentucky EPSCoR cluster grant, and the University of Kentucky, to D.H. from Swedish Forestry and Agricultural Research Council (SJFR/ Formas), Carl Tryggers Stiftelse, Crafoordska Stiftelsen, and Lund University, and to J.W. from NSF grant IBN-9905679. We appreciate many helpful comments on the MS from Ann Baker, Damon Orsetti, Lars Råberg, Bill Searcy, Ian Stewart, Simon Verhulst and two anonymous reviewers. All manipulations to animals were approved by the University of Kentucky IACUC (protocol no. 97–0004L).


  • Antibodies
  • Hormones
  • Immunocompetence handicap
  • Sexual selection
  • Signals

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Animal Science and Zoology


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