a natural experiment on the condition-dependence of achromatic plumage reflectance in black-capped chickadees一个自然实验的消色差羽毛反射率condition-dependence吃教美洲山雀.pdfVIP

A Natural Experiment on the Condition-Dependence of Achromatic Plumage Reflectance in Black-Capped Chickadees 1 2,3 2 1 Liliana D’Alba *, Caroline Van Hemert , Colleen M. Handel , Matthew D. Shawkey 1 Department of Biology and Integrated Bioscience Program, University of Akron, Akron, Ohio, United States of America, 2 U. S. Geological Survey, Alaska Science Center, Anchorage, Alaska, United States of America, 3 Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, Alaska, United States of America Abstract 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 m