Paper List

期刊: ArXiv Preprint
发布日期: 2026-03-14
BiophysicsBio-inspired Materials

Countershading coloration in blue shark skin emerges from hierarchically organized and spatially tuned photonic architectures inside skin denticles

City University of Hong Kong | Max Planck Institute of Colloids and Interfaces | University of Salzburg | B CUBE – Center for Molecular Bioengineering | Elasmobranch Research Belgium (ERB) | Medical University Innsbruck | AZTI, Basque Research and Technology Alliance (BRTA) | Hong Kong Polytechnic University

Viktoriia Kamska, Emeline Raguin, Bodo D. Wilts, Luca Bertinetti, Chiara Micheletti, Clemens Schmitt, Shahrouz Amini, Maria Murace, Frederik H. Mollen, Michael Blumer, Maite Erauskin Extramiana, Ruien Hu, Stefan Redl, Mason N. Dean
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IN SHORT: This paper solves the core problem of how blue sharks achieve their striking dorsoventral countershading camouflage, revealing that coloration originates not from dermal pigments but from hierarchical photonic architectures within individual skin denticles.

核心创新

  • Biology Identifies denticles as the primary optical units ('pixels') for shark skin coloration, overturning the assumption that coloration originates from underlying dermal chromatophores.
  • Methodology Establishes a multi-scale correlative imaging pipeline (optical, μCT, histology, FIB-SEM, TEM) to link nanoscale crystal organization with macroscopic color gradients.
  • Biology Demonstrates a spatial gradient in photonic architecture: from ordered purine-crystal stacks (blue) to disordered assemblies (white), coupled with systematic changes in chromatophore composition and pulp cavity volume (25% in blue zone vs. 17% in white zone).

主要结论

  • Blue shark countershading originates from denticle-embedded photonic architectures, not dermal pigments, with pulp cavity volume decreasing from 25% (blue) to 17% (white).
  • Color variation is organized hierarchically: at the microscale, blue denticles contain a tessellated reflector-absorber system (iridophores + melanophores), while white denticles lack melanophores entirely.
  • At the nanoscale, ordered purine-crystal stacks (~10-60 nm features) generate narrowband blue reflection, whereas disordered assemblies produce broadband white scattering, directly linking crystal organization to optical output.
研究空白： Previous studies focused on shark denticle morphology for hydrodynamics or pigmentation anomalies, largely overlooking their potential role in structural coloration. The physical mechanism behind the blue shark's iconic countershading remained unknown.

摘要: The blue shark (Prionace glauca) exhibits a striking dorsoventral color gradient, transitioning from vibrant blue dorsally to silver and white ventrally—a pattern widely interpreted as pelagic countershading. Despite its ecological significance, the physical basis of this coloration remains unresolved. Here we show that this color system does not arise from dermal chromatophores, as in most vertebrates, but from a previously unrecognised photonic architecture housed within the pulp cavity of individual dermal denticles that cover the skin. Optical imaging reveals discrete color domains within denticle crowns, while external denticle morphology remains similar across color zones. Using spectroscopy, micro-computed tomography, histology and correlative electron microscopy, we demonstrate that color variation is organized across coupled micro- and nanoscale architectures. In blue denticles, iridophores and melanophores form a densely packed tessellated reflector–absorber system within an expanded crown-restricted pulp cavity. Transition-zone denticles exhibit partial cellular layering, whereas white denticles lack melanophores and contain only reflective cells. At the nanoscale, ordered purine-crystal stacks generate narrowband blue reflection, whereas disordered assemblies produce broadband white scattering. Together, these results reveal denticles as mechanically protected optical “pixels” whose hierarchical cellular and nanocrystal organization generates the shark’s countershaded coloration.