GELIFES Seminars - Gregor Belušič

Gregor Belušič (University of Ljubljana)

Colour coding in butterfly retinal mosaics

Insect compound eyes have evolved to sample the world with remarkable efficiency. Their building blocks, the ommatidia, are equivalent to light sensors in a tiny camera, which creates panoramic images with only a few thousand pixels. In butterflies, the most colourful insects with exceptional colour vision, the ommatidia form highly diverse, species- and sex-specific retinal mosaics.
Using single-cell electrophysiology, ophtalmoscopic imaging, electron microscopy, and connectomics, we uncovered that the largest butterfly family, Nymphalidae, evolved two main versions of retinal mosaic. The simple type has three photoreceptor classes (UV, blue, green) arranged into three ommatidial types, supporting two colour-opponent channels (UV-green, blue-green). The complex type, which is likely ancestral, is based on a red-shifted green opsin and a red screening pigment, expanding to six ommatidial types and a green–red opponent channel. Opsin coexpression further tunes receptor sensitivity across the visual field. The downstream neural network in the first optical ganglion is surprisingly complex, with numerous inter-photoreceptor inhibitory synapses that mediate colour opponency.
Despite this complexity, all information is funneled through relatively few neural fibres, yet it suffices for the butterflies’ dazzling colour vision. Their eyes exemplify how evolution sculpts miniature sensory systems to encode rich, private visual worlds in the tiny insect brains.

Biosketch:
Gregor Belušič is a professor of Animal Physiology at the University of Ljubljana. He runs the world-leading lab for the physiological analysis of the early visual pathway in various insects, from mosquitoes and flies to butterflies and beetles. He currently collaborates with research labs from across the EU, USA, Australia and Japan.