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Fine structure of ommatidia at the dorsal eye margin of Calliphora erythrocephala meigen (Diptera: Calliphoridae): An eye region specialised for the detection of polarized light

1982; Elsevier BV; Volume: 11; Issue: 1 Linguagem: Inglês

10.1016/0020-7322(82)90035-6

1872-907X

Hansjörg Wunderer, Ulrich Smola,

Insect behavior and control techniques

The fine structure of the visual cells near the dorsal edge of the eye of the blow fly, Caliphora erythrocephala (Diptera: Calliphoridae) was examined for special features related to the detection of plane-polarized light from the sky. These marginal ommatidia exhibit distinct morphological differences from the neighboring normal ommatidia, as follows. The cross-sectional areas of the somata and rhabdomeres of their peripheral visual cells R1-6 are reduced, though the length is normal, ca. 200 μm. In some cases, the number of cells is also reduced. The central rhabdomeres R7/8 in the marginal ommatidia are only about half as long as those of the remaining ommatidia, but their cross-sectional areas are so much larger that there is a considerable increase in volume. Rhabdomeres R7/8 in the marginal ommatidia do not twist, in contrast to rhabdomeres R1-6 in the same ommatidia and to the normal central rhabdomeres in other parts of the eye, which twist in a characteristic way. The central visual cells of the marginal ommatidia have all the structural prerequisites for high polarization sensitivity. The microvilli of R7 (and R8) throughout the dorsal marginal zone are oriented so as to fan out from the vertex of the eye. Unlike normal ommatidia, the 2 ommatidia nearest the edge in each arc send out axons in a “double pseudocartridge”, an arrangement suggesting special connectivity of these ommatidia. From these findings it is concluded that the dorsal marginal region functions specifically in relation to the detection of polarized sky light. The possible functional involvement of this region in setting the flight path by the sky-light polarization pattern is discussed with reference to two models.