Sexual ornaments are often considered honest signals of quality because potential costs or constraints prevent their display by low-quality individuals. Testing for potential physiological costs of ornaments is difficult, as this requires experimentally forcing individuals to produce and display elaborate ornaments. We use this approach to test whether a sexually selected trait is physiologically costly to male superb fairy-wrens (Malurus cyaneus). Male fairy-wrens molt from brown to blue breeding plumage at different times of the year, and females strongly prefer the few males that are blue early, during winter. We used short-acting testosterone implants to stimulate males to produce “early-blue” plumage and assessed costs during and after molt using a panel of physiological indices. Testosterone-implanted, T-males molted in winter and produced blue plumage 6 weeks before control-implanted, C-males. T-males molted while in lower body condition, tended to have lower fat reserves, and were more likely to be parasitized by lice. However, we detected no negative effects on immune function, blood parasites, exposure to stressors, or survival. Juvenile males never naturally display early-blue plumage, but we found no evidence for increased costs paid by juvenile T-males. Instead, juvenile T-males molted later than adult T-males, suggesting that age presents an absolute constraint on ornament exaggeration that cannot be fully overcome by testosterone treatment. Together, these small costs and large, age-related constraints may enforce signal honesty, and explain female preference for early-blue males.

中文翻译：

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性装饰品的生理成本和年龄限制：对野生鸟类的实验研究

性装饰品通常被认为是质量的诚实信号，因为潜在的成本或限制因素会阻止低质量的人展示性装饰品。测试装饰品的潜在生理成本非常困难，因为这需要通过实验迫使个人生产和展示精美的装饰品。我们使用这种方法来测试性选择的性状是否对雄性精湛的雄性wr（Malurus cyaneus）造成生理上的损失）。在一年中的不同时间，雄性fairy虫从棕色到蓝色的繁殖羽毛会蜕皮，而雌性强烈偏爱冬季较早的少数雄性蓝色。我们使用短效睾丸激素植入物刺激雄性产生“早蓝”羽毛，并使用一组生理指标评估了蜕皮期间和蜕皮后的成​​本。植入睾丸激素的T型雄性在冬天蜕皮，并在植入对照睾丸的C型雄性前6周产生蓝色羽毛。T型雄性在下半身时蜕皮，往往具有较低的脂肪储备，并且更有可能被虱子寄生。但是，我们未发现对免疫功能，血液中的寄生虫，暴露于应激源或存活没有负面影响。少年雄性从来没有自然地表现出早蓝色的羽毛，但我们没有发现证据表明少年T型雄性付出了更多的代价。反而，幼年T型雄性蜕皮的时间要比成年T型雄性蜕皮的时间晚，这表明年龄对装饰物的夸张有绝对的限制，而睾丸激素治疗是无法完全克服的。这些较小的成本以及与年龄相关的较大限制可能共同增强了信号的诚实性，并解释了女性偏爱早蓝的男性。