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The biochemical basis of the sexual ornaments of the red grouse unravels their informative content

The carotenoid-based ornaments displayed by many birds often play key roles in social and sexual signalling, revealing information about individual quality. Understanding the mechanisms of coloured trait production and maintenance requires an accurate description of their composition and of the physiological pathways involved in their expression. Carotenoid-based colouration has been extensively studied in birds, but such information is often lacking for coloured integuments other than feathers, such as fleshy carotenoid based ornaments. We report the carotenoid composition of the combs of the red grouse (Lagopus lagopus scoticus), a sexual trait that honestly reveals individual quality. We found that comb pigmentation was primarily the result of two red ketocarotenoids (astaxanthin and papilioerythrinone), which are synthesised from their dietary precursors (zeaxanthin and lutein) directly at the comb integument. These red ketocarotenoids are largely deposited esterified with fatty acids. Astaxanthin concentration in the comb was found to negatively correlate with retinol levels but positively correlate with tocopherol levels. Considering evidence from this and other studied species, we suggest that carotenoid esterification is a characteristic of coloured fleshy integuments, probably affecting pigment stability and colouration in living tissues, with subsequent effects on their signalling role and maintenance costs. Honest signalling via comb colouration appears mostly related to potential allocation trade-offs of some specific dietary precursors or to the capacity of individuals to manage the redox reactions interfering with carotenoid metabolism.

The results of this study have been published in the online version of Journal of Ornithology, within an article signed by Lorenzo Pérez-Rodríguez, Esther García-de Blas, Jesús Martínez-Padilla, Francois Mougeot and Rafael Mateo, entitled " Carotenoid profile and vitamins in the combs of the red grouse (Lagopus lagopus scoticus): implications for the honesty of a sexual signal ". The PDF of the online version of this paper is available on the left-side panel of this page.



  • Sonja Ludwing holding a male grouse (Photo: Lorenzo Pérez)
  • Male grouse displaying his combs (Photo: Rocío tarjuelo)
  • J. Martínez-Padilla and S. Ludwig catching grouse (Photo: L. Pérez)
  • Male red grouse (Photo: Lorenzo Pérez)