The evolution and function of insect visual opsins

The ability to see the colours of the world notably stems from the functional diversity of light-sensitive receptor genes in the eyes: the opsins. Colour vision relies on opsin number, functions, and expression patterns, granting the peripheral sensory visual system the ability to discriminate different wavelengths of light. Here we explore the interplay between evolutionary constraints and adaptive spectral trajectories across lepidopteran insect families with distinct ecologies and variable reliance on colours for essential visually-guided behaviours. Using a cell-based expression platform together with targeted and helix mutagenesis, we are starting to tease apart the genotype-phenotype relationships underlying opsin spectral tuning and peripheral visual adaptations in diurnal and nocturnal species. Our results pinpoint key residues and several mechanisms underlying changes in ultraviolet (UV) short-wavelength (SW), and long-wavelength (LW) opsin functions. For instance, in diurnal butterfly species equipped with duplicate SW or LW 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, trichromatic moth pollinator systems exhibit residue tuning for finer flower stimulus to background chromatic discrimination. Beyond fascinating lepidopteran systems, the natural diversity of Gq opsins is now amenable to molecular and functional deorphanizing towards the discovery of new types of light-sensing proteins. Merging advances in molecular genetics research on peripheral visual receptors promises to ultimately contribute to understand the functional and regulatory basis of evolutionary adaptations underlying the full palette of invertebrate sensory visual phenotypes.