Journal Article

Testosterone, immunocompetence, and honest sexual signaling in male red grouse

François Mougeot, Justin R. Irvine, Linzi Seivwright, Steve M. Redpath and Stuart Piertney

in Behavioral Ecology

Published on behalf of International Society for Behavioral Ecology

Volume 15, issue 6, pages 930-937
Published in print November 2004 | ISSN: 1045-2249
Published online November 2004 | e-ISSN: 1465-7279 | DOI: http://dx.doi.org/10.1093/beheco/arh087
Testosterone, immunocompetence, and honest sexual signaling in male red grouse

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  • Evolutionary Biology
  • Ecology and Conservation
  • Zoology and Animal Sciences

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The expression of sexual ornaments has been suggested to reliably indicate individual quality, such as the ability to cope with parasites and diseases. The Immunocompetence Handicap Hypothesis (IHH) states that testosterone-dependent ornaments honestly signal such quality because of physiological costs associated with testosterone, such as impaired immune function. We tested predictions of the IHH both correlatively and experimentally in red grouse Lagopus lagopus scoticus. Male grouse exhibit supra-orbital red combs whose size is testosterone-dependent. We found that comb size was not correlated to infection intensity by two parasites (coccidia and the nematode Trichostrongylus tenuis), but it was significantly positively correlated with condition and T-cell-mediated immunity (the ability to mount a primary inflammatory response). We manipulated testosterone by means of implants and re-caught males after a month to investigate the effects on comb size, condition, immunity, and parasite load. Males implanted with testosterone had increased comb size, lost more condition, and had lower T-cell-mediated immunity than control males. Increased testosterone also resulted in a significant increase in coccidia infection intensity but had no effect on T. tenuis burden. The results are consistent with predictions of the IHH and suggest that comb size honestly indicates immunocompetence and males' ability to cope with certain parasites. Females could thus benefit from choosing mates based on the expression of this sexual trait.

Keywords: Immunocompetence Handicap Hypothesis; parasite; red grouse; sexual ornament; T-cell-mediated immunity; testosterone

Journal Article.  6584 words.  Illustrated.

Subjects: Evolutionary Biology ; Ecology and Conservation ; Zoology and Animal Sciences

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