Department of Biology and Integrated Bioscience Program, University of Akron, Akron, Ohio, United States of America.
PLoS One. 2011;6(10):e25877. doi: 10.1371/journal.pone.0025877. Epub 2011 Oct 3.
Honest advertisement models posit that only individuals in good health can produce and/or maintain ornamental traits. Even though disease has profound effects on condition, few studies have experimentally tested its effects on trait expression and even fewer have identified a mechanistic basis for these effects. Recent evidence suggests that black and white, but not grey, plumage colors of black-capped chickadees (Poecile atricapillus) are sexually selected. We therefore hypothesized that birds afflicted with avian keratin disorder, a condition that affects the beak and other keratinized tissues, would show reduced expression of black and white, but not grey, color. UV-vis spectrometry of black-capped chickadees affected and unaffected by avian keratin disorder revealed spectral differences between them consistent with this hypothesis. To elucidate the mechanistic bases of these differences, we used scanning electron microscopy (SEM), electron-dispersive x-ray spectroscopy (EDX) and a feather cleaning experiment. SEM showed extreme feather soiling in affected birds, and EDX revealed that this was most likely from external sources. Experimentally cleaning the feathers increased color expression of ornamental feathers of affected, but not unaffected, birds. These data provide strong evidence that black and white color is an honest indicator in chickadees, and that variation in feather dirtiness, likely due to differences in preening behavior is a mechanism for this association.
诚实的广告模型假设只有身体健康的个体才能产生和/或维持装饰性特征。尽管疾病对健康状况有深远的影响，但很少有研究实验测试它对特征表达的影响，更少的研究确定了这些影响的机制基础。最近的证据表明，黑头山雀（Poecile atricapillus）的黑白而非灰色羽毛颜色是性选择的。因此，我们假设患有鸟类角蛋白紊乱的鸟类，这种疾病会影响喙和其他角蛋白组织，其黑白颜色的表达会减少，而灰色颜色不受影响。受和不受鸟类角蛋白紊乱影响的黑头山雀的紫外线可见光谱分析显示，它们之间存在与这一假设一致的光谱差异。为了阐明这些差异的机制基础，我们使用了扫描电子显微镜（SEM）、电子分散 X 射线光谱（EDX）和羽毛清洁实验。SEM 显示受影响的鸟类的羽毛极度污染，EDX 表明这很可能来自外部来源。实验性地清洁羽毛增加了受影响但不受影响的鸟类的装饰性羽毛的颜色表达。这些数据提供了强有力的证据，证明黑白颜色在山雀中是一个诚实的指标，而羽毛污垢的变化，可能是由于梳理行为的差异，是这种关联的一种机制。
