Meeting Abstract
Stomatopod crustacean have tripartite compound eyes, each with a dorsal and ventral hemisphere separated by two to six ommatidial rows called the midband. The structure and function of the retina have been studied extensively, but the organization of the optic lobe is less well documented. Using reduced silver staining, Golgi impregnation and fluorescent tracers, we show that in Squilla empusa, a species that has two midband rows, the optic lobe organization follows the malacostracan ground pattern. The lamina, medulla and lobula are composed of small columnar subunits that retinotopically correspond to inputs from each ommatidium of the compound eyes. Photoreceptor projections from the midband supply two enlarged lamina cartridges lying adjacent to those of the ventral hemisphere. A gap in the lamina exists at the location of the missing lamina cartridges of the four rows of color-processing channels. Projections from the remaining two midband rows can be traced through the entire optic lobe, as they stain more darkly with reduced silver. At the medial end of the optic lobe, outputs from the dorsal and ventral hemispheric laminas supply the medulla on its dorsal and ventral halves respectively. These neurons then project horizontally in the medulla, and each crosses with the midband lamina projections at the midline. Fluorescent tracer studies targeting this region show increased axonal arborizations at each intersection between these crossing projections, indicating potential for crosstalk between the midband and the dorsal and ventral hemispheres. Our results support the concept that two midband row species are derived from an ancestor that had six midband rows. Visual information from distinct eye regions appears to be combined in the medulla, permitting comparison of visual inputs to all three retinal regions.
