title: Colour-producing β-keratin nanofibres in blue penguin (Eudyptula minor) feathers.
abstract: The colours of living organisms are produced by the differential absorption of light by pigments (e.g. carotenoids, melanins) and/or by the physical interactions of light with biological nanostructures, referred to as structural colours. Only two fundamental morphologies of non-iridescent nanostructures are known in feathers, and recent work has proposed that they self-assemble by intracellular phase separation processes. Here, we report a new biophotonic nanostructure in the non-iridescent blue feather barbs of blue penguins (Eudyptula minor) composed of parallel β-keratin nanofibres organized into densely packed bundles. Synchrotron small angle X-ray scattering and two-dimensional Fourier analysis of electron micrographs of the barb nanostructure revealed short-range order in the organization of fibres at the appropriate size scale needed to produce the observed colour by coherent scattering. These two-dimensional quasi-ordered penguin nanostructures are convergent with similar arrays of parallel collagen fibres in avian and mammalian skin, but constitute a novel morphology for feathers. The identification of a new class of β-keratin nanostructures adds significantly to the known mechanisms of colour production in birds and suggests additional complexity in their self-assembly.
authors.affiliation: Department of Biology and Integrated Bioscience Program, University of Akron, Akron, OH 44325-3908, USA.
authors.forename: Liliana
authors.initials: L
authors.lastname: D'Alba
authors.forename: Vinodkumar
authors.initials: V
authors.lastname: Saranathan
authors.forename: Julia A
authors.initials: JA
authors.lastname: Clarke
authors.forename: Jakob A
authors.initials: JA
authors.lastname: Vinther
authors.forename: Richard O
authors.initials: RO
authors.lastname: Prum
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Shawkey
mesh_terms: D000818:Animals; D003116:Color; D005241:Feathers / Q000737:chemistry* / Q000648:ultrastructure; D046529:Microscopy, Electron, Transmission; D057139:Nanofibers / Q000737:chemistry*; D046429:Spheniscidae / Q000033:anatomy & histology*; D053800:beta-Keratins / Q000737:chemistry*
chemical_list: D053800:beta-Keratins