Intra-sexual competition alters the relationship between testosterone and ornament expression in a wild territorial bird.
In a reliable signalling system, individual quality is expected to mediate the costs associated with ornamental displays, with relatively lower costs being paid by individuals of higher quality. These relative costs should depend not only on individual quality, but also on levels of intra-sexual competition. We explored the current and delayed effects that testosterone implants have on bird ornamentation in populations with contrasted population densities, as a proxy for intra-sexual competition. In a replicated experiment, we manipulated testosterone in 196 yearling male red grouse Lagopus lagopus scoticus in autumn in populations of high and low levels of intra-sexual competition. Males were assigned to one of three exogenous testosterone (T) treatments: empty implants (T0), small T implants (T1) or larger T implants (T2). We monitored subsequent changes in testosterone levels, ornament size and carotenoid-based colouration, carotenoid levels and body condition from autumn to spring. Testosterone implants increased testosterone levels, comb redness and comb size, and decreased body condition but these effects depended on levels of intra-sexual competition. Specifically, T2-implanted birds increased testosterone levels and comb size more, and reduced body condition more, in populations where intra-sexual competition was low. In the following spring, testosterone levels of T2-treated birds kept increasing in populations where intra-sexual competition was high but not in populations where intra-sexual competition was low. Our results highlight that levels of intra-sexual competition alter the relationship between testosterone levels and ornament expression, influencing their condition-dependence; they also indicate that the outcome of standard hormone manipulation conducted in free-living animals vary depending on the population context.
Department of Evolutionary Ecology, Museo Nacional de Ciencias Naturales, José Gutiérrez Abascal, 2, 23005, Madrid, Spain. Electronic address: jmartinezpadilla12@gmail.com.
J
J
Martínez-Padilla
Instituto de Investigación en Recursos Cinegéticos, IREC (CSIC, UCLM, JCCM), Ronda de Toledo, s/n, 3005 Ciudad Real, Spain; Department of Evolutionary Ecology, Estación Biológica de Doñana, (EBD-CSIC), Avda. Americo Vespucio, s/n, 41092 Seville, Spain.
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L
Pérez-Rodríguez
Instituto de Investigación en Recursos Cinegéticos, IREC (CSIC, UCLM, JCCM), Ronda de Toledo, s/n, 3005 Ciudad Real, Spain; Estación Experimental de Zonas Áridas (CSIC), Ctra. de Sacramento s/n, La Cañada de San Urbano, 04120 Almería, Spain.
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F
Mougeot
Game & Wildlife Conservation Trust, Eggleston Hall, Barnard Castle, DL12 0AG UK.
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S
Ludwig
School of Biological Sciences, University of Aberdeen, Tillydrone Avenue, Aberdeen AB24 2TZ, UK.
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SM
Redpath
D000818:Animals; D002338:Carotenoids / Q000378:metabolism; D003116:Color; D003129:Comb and Wattles / Q000187:drug effects / Q000254:growth & development / Q000502:physiology; D003163:Competitive Behavior / Q000502:physiology*; D005241:Feathers / Q000502:physiology*; D005260:Female; D046094:Galliformes / Q000469:parasitology / Q000502:physiology*; D008297:Male; D009348:Nematoda; D010271:Parasites; D012621:Seasons; D012726:Sexual Behavior, Animal / Q000502:physiology*; D013739:Testosterone / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*
D002338:Carotenoids; D013739:Testosterone
Condition-dependence; Hormones; Males; Red grouse; Sexual selection