Why do flies have red eyes? This was the central inquiry of my graduate studies at the University of Wisconsin - Madison from 1969 to 1973. My Ph.D. mentor was a noted electrophysiologist interested in sensory coding, Gerald S. Wasserman. I investigated the Drosophila eye using electrophysiology, one of the most powerful techniques of neuroscience. Taking advantage of Drosophila's eye color mutants, I determined the absorbance of eye color pigments and their effects on visual sensitivity. Many years later, when I incorporated ultrastructural techniques into my interdisciplinary approach, I investigated the eye color pigment granules in normal and eye color mutant Drosophila. I showed that the transparency of granules in pigmented eyes was due to pigments "falling out" of the granules. Also I described the unusual "pigment granules," some with complex substructure, in white-eyed mutants. Eyes which are mosaic because of excision of a transposable element in Drosophila mauritiana have patches with both pigment types. Optical techniques allow the diagnosis of eye color mosaicism caused by heterochromatic position effect variegation in compound eyes and ocelli.

Early papers on the eye color pigments and spectral sensitivity:

Stark, W.S. and Wasserman, G.S. Transient and receptor potentials in the electroretinogram of Drosophila. Vision Research, 1972, 12, 1771-1775. PubMed

Stark, W.S. Effect of eye color pigments on the action spectrum of Drosophila. Journal of Insect Physiology, 1973, 19, 999-1006. PubMed

Stark, W.S. and Wasserman, G.S. Wavelength-specific ERG characteristics of pigmented- and white-eyed strains of Drosophila. Journal of Comparative Physiology, 1974, 91, 427-441.

Later papers on the eye color pigments:

Stark, W.S. and Sapp, R. Eye color pigment granules in wild-type and mutant Drosophila melanogaster. Canadian Journal of Zoology, 1988, 66, 1301-1308.

Stark, W.S., Sapp, R. and Haymer, D.S. Eye color pigment granules in Drosophila mauritiana: Mosaics produced by excision of a transposable element. Pigment Cell Research, 1989, 2 86-92. PubMed

Research notes on eye color mosaicism in compound eye and ocelli:

Stark, W.S., Srygley, R.G. and Greenberg, R.M. Analysis of a compound eye mosaic of outer rhabdomeres absent marked with cardinal. Drosophila Information Service, 1981, 56, 132-133.

Antoine, M.L., Itoku, K.A. and Stark, W.S. How developmentally related are photoreceptors and pigment cells in Drosophila compound eyes? Drosophila Information Service, 1983, 59, 13-14.

White,R.J., J. C. Eissenberg, and W.S. Stark. Eye color mosaicism in ocelli in variegating lines of Drosophila melanogaster. Drosophila Information Service, 1997, 80, 13-14.

Distal TEM showing many pigment granules appear clear in red-eyed flies. Underfocus ring (arrow) demonstrates hole in section. Chatter suggests that granules break upon sectioning. c=cornea, PC=pseudocone, p=primary pigment cell, s=secondary pigment cell, R=rhabdomere, SC-Semper cell. From Stark et al., 1988.

Using optical neutralization of the cornea, pigmented primary pigment cells, secondary pigment cells and receptor cells can be individually identified in eye color pigment mosaics.

A giant "pigment granule" in a white-eyed Drosophila (from Stark and Sapp, 1988)

An ocellus mosaic for eye color pigment (from White et al, 1997)

A compound eye mosaic for eye color pigment

QuickTime Movie (3.4 Mb) through fruit fly compound eye mosaic for eye color pigmentation from P-element insert on fourth chromosome. The transgenic stock (118E-55) is from Sally Elgin at Washington University.The animation was prepared by Rong Wang and Charles Deutch. Note that the depth-focus ("z") series of the eye using the technique of "optical neutralization of the cornea" reveals identifyable primary and secondary pigment cells with pigment in a white background (as well as R1-6 & R7 rhabdomeres).


My master's and doctoral work, under Jerry Wasserman at Wisconsin, was on the effects of eye color pigments on electrophysiological sensitivity. My wife Sharon typed my MA thesis and, since she worked at Xerox, and we copied and collated it on their new automatic machine. My committee had lots of suggestions on the first few pages but did not notice that p 90 was missing because the copier goofed. I was replicating in Drosophila Tim Goldsmith's (Yale) house fly study "Do flies have a red receptor?" on Drosophila. Deric Bownds, on my M.A. committee, gave me a hard time with "what are you going to do when you grow up?" -- implying that Tim could have done what took me a year in a week. My committee all signed off under "did not pass" and I had to chase tham down as they were leaving for vacations with a new copy. Later, I was taking an insect physiology course from Stanley Beck, and Stan Carlson was the substitute teacher when Beck was away. Stan had worked on insect vision, and he agreed to take some slides I made to Sweden for some microspectrophotometry, data I put in my dissertation. I later had many years of friendly collaboration with Stan. My wife Sharon asked "when are you going to write your thesis?" and I said "When the ice melts" since it was a good year for skating and hockey with friends on Monona bay where we lived. She typed it. She worked at Oscar Mayer, and their print shop agreed to make copies by multilith. I thanked Oscar Mayer in my acknowledgements, and Richard Keesey, on my committee, said "What you really mean is, 'I would like to thank Oscar Mayer for all the bologna in this thesis.'" At my defense, Cliff Gilman asked "Why do flies have red eyes?" and my mentor Jerry Wasserman thought that question was silly but I answered it anyway. Since I had many copies, I sent copies to all the famous people in insect vision, and I was nervous about being so forward. But half a year later, Helmut Langer wrote, "Late, I would like to thank you...mind if I use your graph in my review article?" A year later, I came to work a few weeks with Stan Carlson since he had obtained his own microspectrophotometer. I met Reinhard Paulsen who was working with Deric Bownds. I tried to study visual pigments with thin slices as Langer had done, and Reinhard suggested thick slices. Neither aproach worked. Although Doekele Stavenga had already published a study showing that Nicholas Franceschini's pseudopupil technique could give good visual pigment data from whole eyes, it would be a few years before I took this approach.

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This page last revised on August 11, 2004