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Behavioral Ecology Advance Access originally published online on June 16, 2004
Behavioral Ecology 2004 15(6):930-937; doi:10.1093/beheco/arh087
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Behavioral Ecology vol. 15 no. 6 © International Society for Behavioral Ecology 2004; all rights reserved

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

François Mougeota, Justin R. Irvinea, Linzi Seivwrighta,b, Steve M. Redpatha and Stuart Piertneyc

a Centre for Ecology and Hydrology, Hill of Brathens, Banchory, Aberdeenshire AB31 4BW, Scotland, United Kingdom, b Department of Biological and Molecular Sciences, University of Stirling, Stirling FK9 4LA, United Kingdom, and c Department of Zoology, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, Scotland, United Kingdom

Address correspondence to F. Mougeot. E-mail: frm{at}ceh.ac.uk.

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.

Key words: Immunocompetence Handicap Hypothesis, parasite, red grouse, sexual ornament, T-cell-mediated immunity, testosterone.


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