Terminations of Photoreceptor Axons from Different Regions of the Compound Eye of the Desert Ant Cataglyphis bicolor

E. P. Meyer, D. R. Nassel
1986 Proceedings of the Royal Society of London. Biological Sciences  
Plates 1-3] The morphology of the photoreceptors from different regions of the desert ant's compound eye is investigated by Golgi-impregnations and anterograde or retrograde haem peptide filling, combined with electron microscopy. A new type of receptor axon is described. This receptor is of the short (svf) type but terminates in the proximal layer of the lamina (epl-C), in contrast to the other short visual fibres, which terminate in the distal layer (epl-A) : Golgi-EM investigations show that
more » ... tigations show that this receptor axon belongs to the small photoreceptor R9. The receptor R9 appears to be pre-and postsynaptic to other receptor axons and to second order neurons. In each ommatidium, the axons of the two long photoreceptors (lvf) R1 and R5 (probably uv-receptors) remain paired down to their terminations in the distal layer of the medulla. The regional specialization of the retina (dorsal rim area (dra), dorsal retina (dr) and ventral retina (vr)) is reflected by the morphology of the receptor terminals and the second order neurons. The lamina underlying the dra consists of only one layer, an extended epl-A; in the remainder of the eye, the lamina is trillyered. In the dra all short visual fibres (svf) are equal in length. The extension of the monopolar cell dendrites is restricted to one cartridge only. In the medulla, the terminals of the lvfs deriving from the dra (R1 and R5) have more extensive arborizations than elsewhere in the eye. I n t r o d u c t io n Ommatidia in the compound eyes of desert ants consist of nine photoreceptor cells. There are two spectral classes of receptor: green-sensitive and uv-sensitive (Mote & Wehner 1980; Labhart 1986). By analogy with findings in the worker bee (Menzel & Blakers 1976) it has been assumed that the axons of the green-sensitive receptors terminate in the first optic neuropile, the lamina, whereas the uv receptors end in the medulla (Meyer 1979, 1984)-It has been shown that only uv receptors are necessary for the perception of polarized light used in compass orientation (Duelli & Wehner 1973)* In order to understand how e-vector information is processed in Cataglyphis, a more detailed anatomical analysis is needed. One question that is still unresolved is that of how many receptors per
doi:10.1098/rspb.1986.0040 fatcat:mdrg43pnb5eozkmtcxsjfiyhv4