bioRxiv preprint doi: https://doi.org/10.1101/799783; this version posted July 4, 2020. The copyright holder for this preprint (which was not certified by peer review) is the author/funder. All rights reserved. No reuse allowed without permission. 1 Microstructures amplify carotenoid plumage signals in colorful tanagers 1 Authors: Dakota E. McCoy1*, Allison J. Shultz1,2,3,4, Charles Vidoudez5, Emma van der Heide1, Sunia 2 A.Trauger5, David Haig1 3 1. Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, MA 02138 2. Informatics Group, Harvard University, 38 Oxford Street, Cambridge, MA 02138 3. Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, MA 02138 4. Ornithology Department, Natural History Museum of Los Angeles County, 900 Exposition Blvd, Los Angeles, CA 90007 5. Small Molecule Mass Spectrometry Facility, Harvard University, 52 Oxford Street (B2), Cambridge, MA 02138 * corresponding author:
[email protected] 4 Abstract: 5 Red, orange, and yellow carotenoid-colored plumages have been considered honest signals of condition. 6 We comprehensively quantified carotenoid signals in the social, sexually-dimorphic tanager genus 7 Ramphocelus using scanning electron microscopy (SEM), finite-difference time-domain (FDTD) optical 8 modeling, liquid chromatography–mass spectrometry (LC-MS), and spectrophotometry. Despite males 9 having significantly more saturated color patches, males and females within a species have equivalent 10 amounts and types of carotenoids. Male, but not female, feathers have elaborate microstructures which 11 amplify color appearance. Expanded barbs enhance color saturation (for the same amount of pigment) by 12 increasing the transmission of optical power through the feather.