Motion and color information processing in the Papilio visual system

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In the previous year, we collected an extensive dataset on the spectral and polarisation properties of the photoreceptors of Parantica sita. This year we classified these receptors into five distinct spectral groups including ultraviolet (UV), blue (B), broad green (bG), narrow green (nG) and double peaking green (dG) photoreceptors. Within each ommatidium there are 8 main photoreceptor positions from R1 to R8. Due to the dye-injection experiments, we were able demonstrate that UV and B photoreceptors only occur at the R1 and R2 positions while other receptors occur in the R3-R8 positions. We also performed a close examination of ommatidial structure using electron microscopy and revealed that ommatidia at the dorsal rim of the eye were more rectangular than ommatidia in other regions of the eye. The microvilli orientation in the ommatidia of the dorsal rim area of the eye seem specialised for enhanced polarisation sensitivity although no electrical recordings have been made in this region of the eye.On the behavioural side, butterflies have proven reluctant to fly while being tethered. We have discovered that the use of optic flow may be useful to increase flight motivation of the butterfly while it is tethered. In contrast to tethered flight, butterflies display enough flight motivation for prolonged experimental runs during free-flight in a netted cage.