Functional characteristics of photoreceptors in the compound eye and ocellus of the desert ant,Cataglyphis bicolor

Abstract

1. Intracellular recordings have been employed to measure the spectral and polarizational sensitivities of retinular cells in the compound eyes and ocelli ofCataglyphis bicolor. 2. In the central part of the compound eye the responses can be grouped into three classes. One type (VIS) has a sensitivity maximum at 506 nm and a mean sensitivity at 347 nm which is 0.7 log units lower. A second type (UV) is maximally sensitive at 347 nm and is weakly depolarized by long wavelength stimuli. The shape of the V log I relation in these cells is dependent on stimulus wavelength. The third type (UV-VIS) is maximally sensitive at 347 nm but shows a high sensitivity (>50%) at 506 nm. The V log I relation measured in this class is not wavelength dependent. 3. 90% of the cells tested showed polarizational sensitivity (PS) ratios ranging from 1.5 to 6. In the VIS class PS in the u.v. was commonly lower than at the 506 nm peak, but when present the e-vector orientations of maximum and minimum PS were similar for the two spectral regions. In the UV-VIS class PS measured with 506 nm stimuli was commonly lower than in u.v., but in this case when PS was present in the response to green the orientations of maximum and minimum PS were different in the two spectral regions. In the UV class PS was present in the u.v. but not detected with green stimuli. 4. It is proposed that the UV-VIS class arises from strong electrical coupling between adjacent UV and VIS class cells. The long wavelength component of the UV cell's response is thought to arise from a similar but weaker interaction. 5. Photoreceptors in the ocelli are similar to the UV class found in the compound eye in terms of spectral and polarizational sensitivities. They differ, however, in that they do not show the depolarizations with intense green stimuli nor is there any mass response from the whole retina at wavelengths longer than 445 nm.