The electrophysiology of photoreceptors in different eye regions of the desert ant,Cataglyphis bicolor

Summary

• 1. The photoreceptors in different parts of the compound eye ofCataglyphis bicolor are characterized by intracellular electrophysiology and a few ERG experiments. In particular, the physiology of the three anatomically and functionally distinct areas of the compound eye, the dorsal rim area (DRA), the dorsal area (DA) and the ventral area (VA), are compared.

• 2. In all parts of the eye tested (see Fig. 1) two spectral types of receptor with sensitivity maxima in the UV (350 nm) and green (510 nm) are present. In the DRA the UV-cells are increased in size relative to the green cells.

• 3. The polarization sensitivity (PS) of UV-cells is significantly higher in the DRA ($\overline {PS} = 6.3$) than in the rest of the eye ($\overline {PS} = 2.9$). In green-cells PS in the DA and VA ($\overline {PS} = 2.2$) is in the same range as in UV-cells (no PS data are available for the DRA) (Fig. 2).

• 4. The photoreceptors exhibit narrow, bell-shaped angular sensitivity functions in all parts of the eye tested. This is in contrast to the DRA of bees and crickets where the ommatidial visual fields are strongly extended. The acceptance angleΔϱ ranges from 3.0° in the frontal eye part to 5.4° in the DRA.

• 5. The present electrophysiological data are in accord with the behavioral evidence that polarized skylight navigation in insects is mediated by the photoreceptors of the DRA forming a two-dimensional system ofe-vector detection.