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Abstract Melanin-based plumage coloration in birds is shaped by pigment composition as well as melanosome morphology and distribution, however, the ways in which these factors together modulate observable color remain poorly understood. We investigate this relationship in the Capuchino Seedeaters (genusSporophila), whose recent, rapid radiation driven by sexual selection resulted in 12 species with diverse coloration patterns. Using scanning electron microscopy (SEM) and micro-computed tomography (µCT), combined with a novel application of Fontana-Masson stain to image melanosomes at high resolution, we characterize melanosome distribution and morphology in several variably colored plumage patches across Capuchino species. Melanosome morphologies followed patch-specific patterns that did not directly correlate with coloration: crown feather melanosomes were larger, more elongated, and had greater percent eumelanin content than those in belly, throat, or dorsum/rump patches. We also observed that dorsal patches had more total melanin than ventral ones, with pigment and coloration patterns suggesting possible signaling and photoprotective roles. More generally, we show how the patch-specific coloration of male Capuchinos is accompanied by differences in melanosome morphology and melanin composition and abundance. Our work highlights the challenges that remain in understanding how the nanoscale mechanisms of melanin-based pigmentation translate into macroscale plumage coloration. 

Nanowires of layered van der Waals (vdW) crystals are of interest due to structural characteristics and emerging properties that have no equivalent in conventional 3D crystalline nanostructures. Here, vapor-liquid-solid growth, optoelectronics, and photonics of GaS vdW nanowires are studied. Electron microscopy and diffraction demonstrate the formation of high-quality layered nanostructures with different vdW layer orientation. GaS nanowires with vdW stacking perpendicular to the wire axis have ribbon-like morphologies with lengths up to 100 micrometers and uniform width. Wires with axial layer stacking show tapered morphologies and a corrugated surface due to twinning between successive few-layer GaS sheets. Layered GaS nanowires are excellent wide-bandgap optoelectronic materials with Eg = 2.65 eV determined by single-nanowire absorption measurements. Nanometer-scale spectroscopy on individual nanowires shows intense blue band-edge luminescence along with longer wavelength emissions due to transitions between gap states, and photonic properties such as interference of confined waveguide modes propagating within the nanowires. The combined results show promise for applications in electronics, optoelectronics and photonics, as well as photo- or electrocatalysis owing to a high density of reactive edge sites, and intercalation-type energy storage benefitting from facile access to the interlayer vdW gaps.