Wavelength-specific ERG characteristics of pigmented- and white-eyed strains ofDrosophila

Summary

Previous electroretinographic (ERG) studies of white-eyed and red-eyed (wild-type)Drosophila melanogaster (Stark and Wasserman, 1972a) yielded results that were in agreement with Goldsmith's (1965) hypothesis that eye-color pigment absorption decreases the recruitment of contributions from peripheral ommatidia into the ERG. These screening pigments therefore produce wavelength-specific differences between these two strains (as well as within the red-eyed strain) in three ERG parameters, namely the magnitudes of the on- and off-transients and the slopes of the receptor potential energy-response functions. In the present study these three ERG parameters were each measured for constant receptor potential magnitudes (to remove the contribution of spectral sensitivityper se) at 13 wavelengths from 350 nm to 650 nm in the following strains:cn (having only pterins),bw (having only ommatins), wild (having both pigment classes), and two white-eyed strains,cn bw andw. Multiple linear regression analyses were carried out in order to determine the relationships between the foregoing three ERG parameters and parameters related to spectral sensitivity. These data lead us to the following conclusions:

• 1. Unexpected wavelength-dependent parameter differences exist in white-eyed flies. The slopes of the energy-response functions and the magnitudes of the transients all systematically vary and all correlate highly with the spectral sensitivity and with each other. This result implicates another spectrally selective factor other than pigment-determined recruitment in the ERG ofDrosophila. Several hypotheses about the nature of this factor are discussed.

• 2. Parameter differences attributable strictly to eye-color pigments were found when wild,cn, andbw strains were compared with white-eyed strains. These parameter differences varied linearly with screening pigment density, and multiple linear regression analyses accurately predicted the differences in spectral sensitivity produced by the eye-color pigments from the parameter differences of transient sizes and energy-response function slopes.