Interdisciplinary Workshop on Sensory Systems
Invertebrate Color Vision

October 23, 2006
3:30 - 5:20 pm
Mechanical Engineering Building (MEC Hall) room 305

The Genetic Basis of Color and Polarization Vision in Stomatopod Crustaceans
3:30-4:20pm

Thomas W. Cronin
Department of Biological Sciences
University of Maryland Baltimore County
Baltimore, Maryland 21250 USA


Photo by Roy L. Caldwell
The stomatopod crustaceans (mantis shrimps) have a set of photoreceptors in their retinas that are uniquely diverse and complex. Up to 16 different spectral classes are present, 10 operating at visible wavelengths (400 to 700 nm) and 6 more functioning in the ultraviolet (320-400 nm). Microspectrophotometric data suggest that each class is based on a different visual pigment, suggesting that as many as 16 different opsin genes should be expressed in the retina. We have begun to characterize the genetic diversity of the stomatopod opsin gene family, using a species for which most of the visual pigments and receptor sensitivities have already been described, Neogonodactylus oerstedii. We extracted RNA from whole retina and amplified putative opsin transcripts using primers. Sequences with unique 3' untranslated regions were used to construct labeled RNA probes for in situ hybridization to cryosections of retina. Initial investigations found numerous different transcripts, all of which localized to middle/long-wavelength receptor classes. Some receptor cell classes bound multiple probes, indicating that more than one opsin class may be expressed in single photoreceptor cells. Phylogenetic analyses of stomatopod opsin diversity show that most of these sequences cluster with other crustacean MWS/LWS opsins.
   

Color Vision and Eye Organization in Butterflies
4:30-5:20pm

Kentaro Arikawa
Department of Evolutionary Studies of Biosystems
The Graduate University for Advanced Studies (Sokendai)
Hayama, Kanagawa 240-0193, Japan

Photo by Kentaro Arikawa

The Japanese yellow swallowtail butterflty, Papilio xuthus, uses color vision when they are searching for food. They are even color constant. Their eyes are equipped with spectral receptors sensitive in the UV, violet, blue, green, red and broad-band wavelength regions. Localization of these receptors in the ommatidia revealed that the eye consists of three spectrally heterogenous types of ommatidia, each containing different sets of receptors. The ommatidia look red, yellow, or fluorescing because of their characteristic pigmentation, which have crucial role for tuning the photoreceptors' spectral sensitivity. The spectral origin of the broad-band receptor is unique: they coexpress green-absorbing and orange-absorbing visual pigments both functioning in the receptor cell at the same time. Its suppressed sensitivity in the UV region is due to the UV absorbing filtering property of the fluorescing pigment, which is 3OH-retinol. We further tested whether all of the six classes of receptors contribute to color vision by measuring the wavelength discrimination ability using the proboscis extension response. Their discrimination is as good as humans, i.e., 1-2 nm, in the wavelength regions around 430, 480, and 560 nm. The result was well explained when we hypothesized that UV, blue, green, and red receptors contributed to the task. The Papilio color vision may be tetrachromatic.