Araujo, P. | Search bioRxiv

bioRxiv2026

Dorsal ocelli set the luminance-dependent operating state of the bumblebee visual system

Despite long-standing hypotheses that insect dorsal ocelli modulate compound-eye processing to support flight stabilization, dim-light navigation, and locomotor speed, the neurophysiological basis of these functions remains unclear. Combining behavioural assays with multi-site local field potential recordings in bumblebees, we tested how ocellar input affects compound-eye processing. Ocellar occlusion impaired orientation precision at dusk, supporting a role for ocelli in dim-light navigation. Under bright daytime skies, occlusion did not affect orientation but reduced flight speed, consistent with a role in locomotor control under high illumination. Neurophysiologically, ocellar occlusion disrupted luminance-dependent scaling across the visual system, most prominently in the medulla. In intact bees, broadband neural power scaled inversely with luminance, decreasing under bright and increasing under dim conditions. When ocellar input was blocked, this relationship reversed, leaving visual-system activity in a high-power, dark-like state even under bright illumination. Ocellar modulation was particularly evident in the green-sensitive pathway, implicated in optic-flow processing and flight-speed regulation, providing a neural correlate of the behavioural speed reduction while UV-sensitive responses remained largely invariant following ocellar occlusion. These findings reconcile disparate views of ocellar function and identify ocelli as regulators of the neural dynamic range supporting orientation in low light and movement control in bright conditions.

neuroscience↗

bioRxiv2026

Modulation of Avian Iridescence via Malanogenesis

The iridescent colors of birds originate in nanoscale feather structures that interact with light. Although the physical principles governing avian iridescence are well-established, the molecular mechanisms assembling these nanostructures into photonic materials remain unknown. Here, we integrated genomic, cellular, and optical approaches to investigate the molecular basis of iridescent color formation in birds. We leveraged mutations that arose in the domesticated Indian peafowl and natural color variation in wild birds. In peafowl, we identified eight genes underlying gains, losses, and shifts of iridescence, whereas in two wild species, we used single-cell transcriptomics to profile asymmetric feathers in which iridescent and non-iridescent barbules develop on opposite sides of the same feather. We found that all peafowl mutations mapped to melanogenesis genes, showing that variation in this pathway can modify diverse geometric features of feather photonic nanostructures. Mutations altering melanin composition collapsed multilayered photonic systems and yielded non-iridescent tissues, whereas changes in melanosome abundance, elongation, or deposition timing generated multilayer architectures with variable periodicity and color. We further show in peafowl that transitions from non-iridescent to iridescent plumage were associated with single-nucleotide mutations in a melanogenesis gene, suggesting that, in species already capable of forming multilayered nanostructures, iridescence can be gained by relatively small genetic changes. Single-cell transcriptomes from wild species also supported extensive melanocyte-centered regulatory rewiring associated with iridescence, including changes in melanosome maturation, trafficking, and intercellular signaling. Together, these results show that the nanoscale order underlying iridescence is developmentally plastic and highly responsive to the melanogenic environment. Significance StatementBird feathers can produce brilliant, shifting colors, but how these colors form during development has remained poorly understood. By comparing the genomes of color variants of domesticated peafowl and transcriptomes during feather development in wild birds, and combining these with chemical and optical analyses, we show that mutations in genes associated with melanogenesis can profoundly alter the amount, shape, and arrangement of the melanin granules inside feathers that interact with light and produce iridescence. These changes can switch feather appearance between dull and iridescent, or generate entirely new colors by restructuring how those granules are layered at the microscopic scale. Our results reveal a direct and flexible link between pigment production and the physical structures that generate iridescence in birds.

evolutionary biology↗