How do Drosophila visual receptors feed in to behavior? Together with students in my laboratory, I used mutants to determine phototactic input of each receptor type in the compound eye and from the ocelli (the simple eyes). By our model, the predominant retinal receptor, R1-6, mediates sensitivity only in dim light while the other two receptor types, including R7, dominate behavior at photopic light levels. R7's predominance explained the attraction of flies to UV light. Ocelli facilitate input from all 3 compound eye receptor types. Do flies have color vision? This is a controversial question whose answers are as diverse as the possible experimental operations. Our data suggested rather that different receptors function at differentl ight levels, much like human rods, which subserve night vision, are overridden by cones in the well-known Purkinje shift at higher light levels.
Here is the optical bench for this work. A standard light (one wavelength, one intensity) shines on the left window of the Y-maze. On the right, a monochromator provides variable wavelengths while a tray of neutral density filters provides variable wavelengths. Here is a close-up of the maze loaded with flies. The guillotine door slides in from the 7 o'clock position. (We never used the side door.)
Before my work with Bill Harris, there had been work on
fly photoreceptor spectral sensitivities. The most recent model
was that R1-6 had UV and blue peaks while R7/8 had a blue peak.
These conclusions came from elegant behavioral studies by Hendrik
Eckert when he was at the Max Planck Institute for Cybernetics
in Tubingen. Also, Reinhard Schumperli found a UV sensitivity
peak for Drosophila phototaxis, and he concluded that this meant
Drosophila had color vision with the UV preference mediated by
interaction of the R1-6 UV-blue mechanism with the R7/8 blue mechanism.
I met Hendrik and Reinhard (Pu) at the 1974 Society for Neuroscience
meeting. My first Ph.D. student, Karin
Hu, (her present home
page) showed, by comparing wild-type with sevenless, that
R7, the UV receptor, mediated the attraction of flies to UV light.
Interestingly, it was not until years later that we could obtain
phototaxis spectra for R1-6, work by Karen Frayer and Greg Miller
using stimuli too dim to see. Karin looked hard for the R1-6 mediated
behavior, and there were lab jokes and photos, "looking for
R1-6." About the time Karin Hu and I were publishing our
finding that R7/8 mediated Drosophila phototaxis, Martin Heisenberg
was publishing a paper stating that most behaviors he was studying
were mediated by R1-6, not R7/8. The editor of Journal of Comparative
Physiology, Hans Joachem Autrum, sent me Martin's paper to referee
and sent Martin ours, while friends were asking me "Bill,
how are your relations with Heisenberg," considering that
the results seemed contradictory. Actually, everything was cordial,
and eventually I met Martin and stayed at his castle in Wurtzburg
in 1978. One result in his 1971 paper had confused me when I wrote
my thesis, so I said "that result seemed backward."
He pulled out the graph and found that the draftsman had labeled
it backward, and that was the first anyone noticed that mistake.
Papers in the phototaxis series:
Stark, W.S., Ivanyshyn, A.M. and Hu, K.G. Spectral sensitivities and photopigments in adaptation of fly visual receptors. Die Naturwissenschaften,1976, 63,513-518. (Invited review).
Hu, K. G. and Stark, W.S. Specific receptor input into spectral preference in Drosophila. Journal of Comparative Physiology, 1977, 121, 241-252.
Hu, K.G. and Stark W.S. The roles of Drosophila ocelli and compound eyes in phototaxis. Journal of Comparative Physiology, 1980, 135, 85-95.
Miller, G.V., Hansen, K.N. and Stark, W.S. Phototaxis in Drosophila: R1-6 input and interaction among ocellar and compound eye receptors. Journal of Insect Physiology, 1981, 27, 813-819.
Comparing with ERG analyses, there is an amazing correspondence of R1-6,R7 and R8 spectra determined by phototaxis and the ERG isolated by mutantsor adaptation.
The original demonstration that R7 mediates an attraction of flies to UV light which is eliminated in sevenless mutants, from Stark et al. (Naturwissenschaften 63, 513-518,1976)
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This page was last updated May 18, 2004