School of Biological Sciences and Center for Reproductive Biology, Washington State University, Pullman, Washington, United States of America.
PLoS One. 2011;6(10):e26067. doi: 10.1371/journal.pone.0026067. Epub 2011 Oct 5.
Sexual signals, such as bright plumage coloration in passerine birds, reflect individual quality, and testosterone (T) may play a critical role in maintaining signal honesty. Manipulations of T during molt have yielded mixed effects on passerine plumage color, in most cases delaying molt or leading to production of drab plumage. However, the majority of these studies have been conducted on species that undergo a post-nuptial molt when T is low; the role of T in species that acquire breeding plumage during a pre-nuptial molt remains largely unexplored.
METHODOLOGY/PRINCIPAL FINDINGS: We experimentally tested the effects of increased T on plumage color in second-year male red-backed fairy-wrens (Malurus melanocephalus), a species in which after-second-year males undergo a pre-nuptial molt into red/black (carotenoid and melanin-based) plumage and second-year males either assume red/black or brown breeding plumage. T treatment stimulated a rapid and early onset pre-nuptial molt and resulted in red/black plumage acquisition, bill darkening, and growth of the sperm storage organ, but had no effect on body condition or corticosterone concentrations. Control males molted later and assumed brown plumage. T treated males produced feathers with similar but not identical reflectance parameters to those of unmanipulated after-second-year red/black males; while reflectance spectra of red back and black crown feathers were similar, black breast feathers differed in UV chroma, hue and brightness, indicating a potentially age and plumage patch-dependent response to T for melanin- vs. carotenoid-pigmentation.
CONCLUSIONS/SIGNIFICANCE: We show that testosterone is the primary mechanism functioning during the pre-nuptial molt to regulate intrasexually variable plumage color and breeding phenotype in male red-backed fairy-wrens. Our results suggest that the effects of T on plumage coloration may vary with timing of molt (pre- vs. post-nuptial), and that the role of T in mediating plumage signal production may differ across age classes, plumage patches, and between pigment-types.
性信号，如雀形目鸟类鲜艳的羽毛颜色，反映了个体的质量，而睾丸激素（T）可能在维持信号真实性方面起着关键作用。在换羽期间对 T 的处理对雀形目鸟类的羽毛颜色产生了混合影响，在大多数情况下，延迟了换羽或导致产生暗淡的羽毛。然而，这些研究大多数都是在 T 水平较低时进行的、经历婚后换羽的物种上进行的；在经历婚前换羽获得繁殖羽的物种中，T 的作用在很大程度上仍未得到探索。
方法/主要发现：我们实验测试了增加 T 对红背仙鹟（Malurus melanocephalus）雄性第二年幼鸟羽毛颜色的影响，这种物种的雄性第二年幼鸟经历婚前换羽，变成红/黑（基于类胡萝卜素和黑色素）羽毛，而第二年雄性幼鸟则获得红/黑或棕色繁殖羽。T 处理刺激了快速和早期的婚前换羽，并导致获得红/黑羽毛、喙部变暗和精子储存器官的生长，但对身体状况或皮质酮浓度没有影响。对照雄性换羽较晚，并获得棕色羽毛。T 处理的雄性产生的羽毛具有与未经处理的雄性第二年红/黑个体相似但不完全相同的反射率参数；虽然红背部和黑色冠羽的反射光谱相似，但黑色胸部羽毛在 UV 色度、色调和亮度上存在差异，表明 T 对黑色素与类胡萝卜素色素的反应可能因年龄和羽毛斑块而异。
结论/意义：我们表明，睾丸激素是在婚前换羽期间调节雄性红背仙鹟内部可变的羽毛颜色和繁殖表型的主要机制。我们的结果表明，T 对羽毛颜色的影响可能因换羽时间（婚前与婚后）而异，并且 T 在介导羽毛信号产生方面的作用可能因年龄类别、羽毛斑块和色素类型而有所不同。
