Meeting Abstract
Visual motion is a particularly valuable cue for insects and other animals with poor spatial acuity, because optic flow provides a way to infer the three-dimensional structure of one’s surroundings without relying on resolving fine detail. Using a virtual-reality system, we have demonstrated that flying swallowtail butterflies (Papilio xuthus) are attracted to targets that create the illusion, via motion parallax cues, of being nearby. However, we found no evidence that they quantitatively estimate the distance of targets. Like many Lepidoptera, Papilio has a rather complex retinal organisation compared to other insects. Its compound eye contains at least six distinct spectral classes of photoreceptors, and based on wavelength discrimination ability, its colour vision appears to be tetrachromatic. This spectral richness has interesting consequences for its motion detection system. By observing optomotor responses in tethered animals, we have found that – unlike most insects studied – Papilio can perceive motion using chromatic contrast in the absence of luminance contrast. Based on modelling results, we believe that this is the result of pooling signals from spectrally heterogeneous short visual fibres. Recently, we have been attempting to understand in detail the neural circuitry between photoreceptors and early visual interneurons. We have undertaken an ambitious project to elucidate the “connectome” of the Papilio lamina from serial block-face scanning electron microscopy (SBF-SEM) data. On the behavioural side, we have been investigating the nature of Papilio‘s colour opponency system by characterising colour induction using a tetrachromatic display system. Preliminary results indicate that blue and green are mutually opponent, at least in females; this sensory system appears to be unexpectedly sexually dimorphic.
