Functional basis of insect visual opsin evolution

Colour vision notably relies on opsin number, functions, and photoreceptor expression patterns that confer the peripheral visual system the ability to discriminate different wavelengths of light. Here, we explore the interplay between evolutionary constraints and adaptive spectral trajectories across sphingid, lycaenid and riodinid lepidopteran families with variable reliance on colours for essential visually guided behaviours. Using an optimized cell-based expression platform together with targeted and helix mutagenesis, we tease apart genotype-phenotype relationships underlying opsin spectral tuning and peripheral visual adaptations in diurnal and nocturnal species. Our results pinpoint residues underlying changes in ultraviolet (UV), short-wavelength (SW), and long-wavelength (LW) opsin functions. In diurnal butterfly species equipped with duplicate opsins, we find evidence that coordinated functional opsin shifts as well as regulatory changes affecting retinal mosaics alter spectral sensitivity for finer intraspecific long-wavelength color discrimination. In contrast, some trichromatic moth pollinator systems exhibit spectral residue tuning for finer flower stimulus-background chromatic discrimination. Beyond fascinating lepidopteran systems, we discuss how the full diversity of Gq opsins is amenable to molecular and functional deorphanizing. Such studies can contribute to deriving general principles underlying the genetic basis and evolution of invertebrate spectral phenotypes and expand our understanding of the full palette of wavelengths perceived and used by organisms.