The spectral sensitivity of the visual cells R7 and R8 in the eye of the blowflyCalliphora erythrocephala

Abstract

1. The spectral sensitivity of the visual receptors R7 and R8 in the eye ofCalliphora erythrocephala was determined by intracellular recording. The cells were reliably identified by intracellular marking with Procion yellow. 2. Cells in these two morphologically defined receptor classes could be assigned to 4 types differing significantly in spectral sensitivity. Both R7 and R8 can be subdivided into two populations on this basis. a. The group of distal central cells, R7, consists of dual-peaked UV-blue receptors, with maxima at about 350 nm and about 440 nm (R7UB); the maximum in the blue is nearly always smaller than the UV maximum, and of single-peaked UV receptors, with a maximum at about 350 nm (R7UV). b. The group of proximal central cells, R8, consists of single-peaked blue receptors (R8B), with a maximum at about 440 nm, and single-peaked green receptors (R8G), with a maximum at about 520 nm; in some cases R8 can exhibit a secondary peak at about 350 nm. 3. The different frequencies of penetrated central visual cells of different spectral sensitivities, lead to the hypothesis of the existence of two different central rhabdomere tandem combinations. These combinations appear in the middle region of the eye in a ratio of R7UB-R8G:R7UV-R8B≈3∶2. 4. It is suggested that the functionally different combinations R7UB-R8G and R7UV-R8B are related to the structurally different central rhabdomeres (sl and ls type; Smola, 1977) (Fig. 10). 5. The different spectral sensitivities of the central receptors R7 and R8 suggest that these receptors are involved in phototactic behaviour and colour vision of the fly.