Testing the interactive effects of testosterone and parasites on carotenoid-based ornamentation in a wild bird

Authors

  • J. MARTÍNEZ-PADILLA,

    1. Aberdeen Centre for Environmental Sustainability (ACES), University of Aberdeen & The Macaulay Institute, School of Biological Sciences, Tillydrone Avenue, Aberdeen, UK
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  • F. MOUGEOT,

    1. Estación Experimental de Zonas Áridas, CSIC, Almería, Spain
    2. Instituto de Investigación en Recursos Cinegéticos (CSIC-UCLM-JCCM), Ciudad Real, Spain
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  • L. M. I. WEBSTER,

    1. School of Biological Sciences, University of Aberdeen, Aberdeen, UK
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  • L. PÉREZ-RODRÍGUEZ,

    1. Instituto de Investigación en Recursos Cinegéticos (CSIC-UCLM-JCCM), Ciudad Real, Spain
    2. School of Biological Sciences, University of Aberdeen, Aberdeen, UK
    3. Departmento de Ecologia Evolutiva, Museo Nacional de Ciencias Naturales (CSIC), Madrid, Spain
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  • S. B. PIERTNEY

    1. School of Biological Sciences, University of Aberdeen, Aberdeen, UK
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Jesus Martinez-Padilla, School of Biological Sciences, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, UK.
Tel.: +44 1224 272693; fax: +44 1224 272396; e-mail: j.mart@abdn.ac.uk

Abstract

Abstract Testosterone underlies the expression of most secondary sexual traits, playing a key role in sexual selection. However, high levels might be associated with physiological costs, such as immunosuppression. Immunostimulant carotenoids underpin the expression of many red-yellow ornaments, but are regulated by testosterone and constrained by parasites. We manipulated testosterone and nematode burdens in red grouse (Lagopus lagopus scoticus) in two populations to tease apart their effects on carotenoid levels, ornament size and colouration in three time-step periods. We found no evidence for interactive effects of testosterone and parasites on ornament size and colouration. We showed that ornament colouration was testosterone-driven. However, parasites decreased comb size with a time delay and testosterone increased carotenoid levels in one of the populations. This suggests that environmental context plays a key role in determining how individuals resolve the trade-off between allocating carotenoids for ornamental coloration or for self-maintenance needs. Our study advocates that adequately testing the mechanisms behind the production or maintenance of secondary sexual characters has to take into account the dynamics of sexual trait expression and their environmental context.

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