The r�le of retinula cell types in visual behavior ofDrosophila melanogaster

Abstract

We propose that inDrosophila melanogaster the optomotor response to both horizontal and vertical movement is mediated predominantly by the 6 large retinula cells (R1–6) in each facet of the compound eye. Evidence is presented which indicates that this may also be true for most of the other visual responses which at present can be quantitatively studied. These responses include visually controlled landing, pattern-induced orientation of flying and walking animals, the abnormal jump reflex of the mutant Hk1 (Kaplan, 1976) and probably also phototaxis. The only function for which the small retinula cells R7 and/or R8 seem to be required so far is spectral wavelength discrimination in phototaxis at high light intensity. Our hypothesis is based on studies of the receptor deficient mutantssevenless, outer rhabdomeres absent andreceptor degeneration B as well as on results of bleaching experiments by which the retinula cells R1–6 of the eye color mutantwhite can be reversibly blocked. Visual performance of wild typeDrosophila in the optomotor response reflects receptor properties (visual acuity, spectral sensitivity and polarization sensitivity) expected for the R1–6 receptor subsystem. The notion of a ‘high sensitivity’ and a ‘high acuity’ state which was proposed earlier on the basis of experiments on various visual mutants is in agreement with the present results but their interpretation as reflecting properties of different receptor subsystems must be abandoned. Experimental data on wild type also suggest the existence of such an adaptational mechanism; this, however, remains to be demonstrated more conclusively.