Is avian humoral immunocompetence suppressed by testosterone? |
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Authors: | Dennis Hasselquist James A Marsh Paul W Sherman John C Wingfield |
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Institution: | (1) Section of Neurobiology and Behavior, Cornell University Seeley G. Mudd Hall, Ithaca, NY 14853-2702, USA, US;(2) Department of Immunology and Microbiology Cornell University, Veterinary Medicine Center, Ithaca NY 14853-2702, USA, US;(3) Department of Zoology, University of Washington, Seattle WA 98195, USA, US |
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Abstract: | A key issue in sexual selection theory is how a correlation between male secondary sexual characters and male genetic quality
can be maintained. The immunocompetence-handicap hypothesis proposes that testosterone-dependent male characters remain honest
signals because of the immunosuppressive effect of elevated steroid hormone levels. The hypothesis requires that physiological
levels of testosterone depress immune system function. We quantified testosterone titers and humoral immunocompetence of captive
male and female red-winged blackbirds (Agelaius phoeniceus) at three points in the annual cycle (autumn, prebreeding, and breeding). We also conducted an implant experiment on the
males to assess the effects of prolonged, above-normal testosterone titers on humoral immune responses. Humoral immunocompetence
was measured as secondary antibody production to a non-pathogenic protein antigen, keyhole limpet hemocyanin, using an enzyme-linked
immunosorbent assay we developed for A. phoeniceus. Secondary antibody responses of individuals were highly repeatable between sampling periods. Neither physiological nor above-normal
levels of plasma testosterone suppressed secondary antibody production. In paired tests of the same individuals between prebreeding
and breeding, and between breeding and implant, plasma testosterone increased significantly but secondary antibody responses
were unaffected. We are confident in these results because with 80% power, an 11–14% difference in antibody titers would have
been detected. There was no relationship between plasma testosterone levels and humoral immunocompetence in free-ranging males
tested at the peak of breeding. These results cast doubt on a key assumption of the immunocompetence-handicap hypothesis.
Received: 13 April 1998 / Accepted after revision: 7 October 1998 |
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Keywords: | Immunocompetence Testosterone Immunosuppression Sexual selection Red-winged blackbird ELISA |
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