Meeting Abstract
The compound eyes of stomatopod crustaceans have unusual ommatidial rows at the equator called the midband that are typically specialized for color and polarization vision. Beneath the retina, this midband specialization is also reflected in the brain, as distinct columns of midband neuropils and their projections can be traced throughout the optic lobe. We studied how this optic lobe morphologically changes from the larva with typical crustacean larval compound eyes, lacking a midband, to an adult with the midband in Alima pacifica. Before metamorphosis, late-stage larvae have double-retina eyes; the developing adult retina sits adjacent to the larval one. Using osmium-ethyl gallate staining, whole-mount immunolabeling, and 3D reconstruction, we show that photoreceptor axons from larval ommatidia project to a larval lamina split into two halves at the equator corresponding to the dorsal and ventral hemispheres of the adult. The halves supply axons to two components of a deeply curved larval medulla that join ventrally beneath the developing adult eye. Outputs from this larval medulla supply a bilobed larval lobula. Photoreceptors of the developing adult eye project to a new adult lamina, outputs of which subsequently supply a new adult medulla located above the joining point of the larval medulla. Axon fibers from this adult medulla pass through a groove in the larval medulla and supply a new adult lobula adjacent to the larval lobula. Our results reveal two independent visual processing pathways in the stomatopod optic lobe during metamorphosis. The adult system replaces the larval one about a week after metamorphosis, when the larval eye, together with its larval lamina, medulla and lobula, completely degenerates.
