| Autor: |
McCoy DE; Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA. dakotamccoy@g.harvard.edu., Shultz AJ; Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA.; Informatics Group, Harvard University, 38 Oxford Street, Cambridge, MA, 02138, USA.; Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA.; Ornithology Department, Natural History Museum of Los Angeles County, 900 Exposition Blvd, Los Angeles, CA, 90007, USA., Vidoudez C; Harvard Center for Mass Spectrometry, Harvard University, 52 Oxford Street (B2), Cambridge, MA, 02138, USA., van der Heide E; Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA., Dall JE; Ornithology Department, Natural History Museum of Los Angeles County, 900 Exposition Blvd, Los Angeles, CA, 90007, USA., Trauger SA; Harvard Center for Mass Spectrometry, Harvard University, 52 Oxford Street (B2), Cambridge, MA, 02138, USA., Haig D; Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA, 02138, USA. |
| Abstrakt: |
Brilliantly-colored birds are a model system for research into evolution and sexual selection. Red, orange, and yellow carotenoid-colored plumages have been considered honest signals of condition; however, sex differences in feather pigments and microstructures are not well understood. Here, we show that microstructures, rather than carotenoid pigments, seem to be a major driver of male-female color differences in the social, sexually-dimorphic tanager genus Ramphocelus. We comprehensively quantified feather (i) color (using spectrophotometry), (ii) pigments (using liquid chromatography-mass spectrometry (LC-MS)), and (iii) microstructures (using scanning electron microscopy (SEM) and finite-difference time-domain (FDTD) optical modeling). Males have significantly more saturated color patches than females. However, our exploratory analysis of pigments suggested that males and females have concordant carotenoid pigment profiles across all species (MCMCglmm model, female:male ratio = 0.95). Male, but not female, feathers have elaborate microstructures which amplify color appearance. Oblong, expanded feather barbs in males enhance color saturation (for the same amount of pigment) by increasing the transmission of optical power through the feather. Dihedral barbules (vertically-angled, strap-shaped barbules) in males reduce total reflectance to generate "super black" and "velvet red" plumage. Melanin in females explains some, but not all, of the male-female plumage differences. Our results suggest that a widely cited index of honesty, carotenoid pigments, cannot fully explain male appearance. We propose that males are selected to evolve amplifiers-in this case, microstructures that enhance appearance-that are not necessarily themselves linked to quality. |
