How do the different visual receptors mediate vision? This was one primary issue underlying my NSF-funded research as Assistant Professor of Psychology at The Johns Hopkins University. These were the early days of a powerful neurobiological approach dubbed "genetic dissection of the nervous system." I was fortunate in my collaboration with Mr. W. A. Harris, a graduate student at Caltech. We used mutants with vs. without specific receptor types to systematically simplify the compound eye. We introduced mutations of important genes: rdgA, rdgB, sev and ora which have been used in hundreds of studies even to this day. I used electrophysiology to determine spectral sensitivities of the 3 types of photoreceptor types in the compound eye: R1-6, R7 and R8. We overturned the previously accepted dogma, introducing a new model of receptor multiplicity which has been confirmed and elaborated upon since that time. Most notably, we were the first to report that one receptor, R7, was an ultraviolet (UV) receptor, a discovery which had evaded a decade and a half of concerted earlier studies. My students and I also determined the properties of the ocelli (small eyes between the compound eyes on the fly's head). This receptor multiplicity has remained of intense interest even to the present era as the differing rhodopsins which we originally characterized have been cloned and studied with molecular techniques.

Selected publications on receptor spectral sensitivity:

Stark, W.S. Spectral selectivity of visual response alterations mediated by interconversions of native and intermediate photopigments in Drosophila. Journal of Comparative Physiology, 1975, 96, 343-356.

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).

Harris, W.A., Stark, W.S. and Walker, J.A. Genetic dissection of the photoreceptor system in the compound eye of Drosophila melanogaster. Journal of Physiology, 1976, 256, 415-439.

Stark, W.S. Sensitivity and adaptation in R7, an ultraviolet photoreceptor, in the Drosophila retina. Journal of Comparative Physiology, 1977,115, 47-59.

Hu, K.G., Reichert, H. and Stark, W.S. Electrophysiological characterization of Drosophila ocelli. Journal of Comparative Physiology, 1978, 126,15-24.

Stark, W.S., Frayer, K.L. and Johnson, M.A. Photopigment and receptor properties in Drosophila compound eye and ocellar receptors. Biophysics of Structure and Mechanism, 1979, 5, 197-209. (Invited review to accompany European Neurosciences Association 1978 Meeting presentation).

Comparing with phototaxis analysis, there is an amazing correspondence of R1-6, R7 and R8 spectra determined by phototaxis and the ERG isolated by mutants or adaptation.

A diagram showing R1-6, R7 and R8 photoreceptors, with their microvillar rhabdomeres, in each ommatidium of the compound eye

The first demonstration (from Stark, 1975) that R7 is a UV receptor, R8 is a blue-green receptor and R1-6 is a UV-blue receptor

A micrograph from Harris et al., 1976, the introduction of the sevenless (sev) mutant

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This page was last updated on January 4, 2000