AN ULTRAVIOLET ABSORBING PIGMENT CAUSES A NARROW-BAND VIOLET RECEPTORAND A SINGLE-PEAKED GREEN RECEPTOR IN THE EYE OF THE BUTTERFLY PAPILIO

The distal photoreceptors in the tiered retina of Papilio exhibit diff erent spectral sensitivities. There are at least two types of short-wa velength sensitive receptors: an ultraviolet receptor with a normal sp ectral shape and a violet receptor with a very narrow spectral bandwid th. Furthermore, a blue receptor, a double-peaked green receptor and a single-peaked green receptor exist. The violet receptor and single-pe aked green receptor are only found in ommatidia that fluoresce under u ltraviolet illumination. About 28% of the ommatidia in the ventral hal f of the retina exhibit the UV-induced fluorescence. The fluorescence originates from an ultraviolet-absorbing pigment, located in the most distal 70 mu m of the ommatidium, that acts as an absorption filter, b oth for a UV visual pigment, causing the narrow spectral sensitivity o f the violet receptor, and for a green visual pigment, causing a singl e-peaked green receptor. (C) 1998 Elsevier Science Ltd. All rights res erved.