International Collaboration on Color Vision in Arthropods

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The specific aim of this international research project was to understand the basic design of color vision system of butterflies. Below are the results obtained from this project.General appearance of ommatidial heterogeneity in butterfliesWe have discovered that the ommatidia of the Japanese yellow swallowtail butterfly, Papilio xuthus are spectrally heterogeneous. We identified at least three types of ommatidia, which are randomly distributed over the retina. The random distribution of different types of ommatidia may be related to their color vision. We therefore observed the tapetal reflection of more than 50 butterfly species, occurring mainly in Taiwan, by using epi-illumination metal microscope. In all species observed, the color and/or intensity of tapetal reflection appeared to be heterogeneous among ommatidia. This clearly indicates that the ommatidial heterogeneity and their random distribution is a general property of butterfly compound eyes. Based on the data obtained, we … More carefully selected several species with which more detailed research will be carried out, and we initiated some pilot experiments.Physiological and molecular biological study of the spectral sensitivities of Papilio photoreceptorIn the Papilio retina, we previously identified a violet receptor whose spectral sensitivity function is considerably narrower compared to other spectral receptors. Here we demonstrated that the violet receptors reside always in the ommatidia emitting strong fluorescence under UV epi-illumination. The fluorescence is due to 3OH hydroxyretinol, which is acting as an UV-absorbing filter. The violet receptors were also shown to contain UV-absorbing visual pigment. This gives a molecular biological support to our previous hypothesis that the violet receptors are produced by UV absorbing visual pigment filtered by the 3-OH hydroxyretinol. Also, we found a novel type of spectral receptor whose spectral sensitivity has a very broad (230 nm in half-bandwidth) sensitivity spectrum in the visible region and completely lacks the sensitivity in the UV wavelength region. Because of the abnormally-broad sensitivity, we termed the cell as A-cell. The spectral origin of the A-cell was also determined. Less