Integrated Bioscience Program, Department of Biology, The University of Akron, Akron, OH 44325, USA.
J Exp Biol. 2011 Jul 1;214(Pt 13):2157-63. doi: 10.1242/jeb.055822.
Honest advertisement models posit that sexually selected traits are costly to produce, maintain or otherwise bear. Brightly coloured feathers are thought to be classic examples of these models, but evidence for a cost in feathers not coloured by carotenoid pigments is scarce. Unlike pigment-based colours, iridescent feather colours are produced by light scattering in modified feather barbules that are characteristically flattened and twisted towards the feather surface. These modifications increase light reflectance, but also expose more surface area for water adhesion, suggesting a potential trade-off between colour and hydrophobicity. Using light microscopy, spectrometry, contact angle goniometry and self-cleaning experiments, we show that iridescent feathers of mallards, Anas platyrhynchos, are less hydrophobic than adjacent non-iridescent feathers, and that this is primarily caused by differences in barbule microstructure. Furthermore, as a result of this decreased hydrophobicity, iridescent feathers are less efficient at self-cleaning than non-iridescent feathers. Together, these results suggest a previously unforeseen cost of iridescent plumage traits that may help to explain the evolution and distribution of iridescence in birds.
诚实的广告模型假设，性选择特征的产生、维持或其他方面都需要付出代价。色彩鲜艳的羽毛被认为是这些模型的典型例子，但关于非类胡萝卜素色素着色的羽毛存在成本的证据很少。与基于色素的颜色不同，虹彩羽毛的颜色是由光在经过修饰的羽小枝中的散射产生的，这些羽小枝的特点是朝向羽毛表面变平并扭曲。这些修饰增加了光的反射率，但也增加了更多的水附著面积，表明颜色和疏水性之间可能存在权衡。使用光学显微镜、光谱学、接触角测角法和自清洁实验，我们表明，鸭 Anas platyrhynchos 的虹彩羽毛比相邻的非虹彩羽毛的疏水性差，这主要是由于羽小枝微观结构的差异造成的。此外，由于疏水性降低，虹彩羽毛的自清洁效率不如非虹彩羽毛。这些结果表明，虹彩羽毛特征存在以前未预料到的成本，这可能有助于解释鸟类虹彩的进化和分布。
