Meeting Abstract
13.5 Tuesday, Jan. 4 Ciliary photoreceptors in the brachiopod Terebratalia transversa PASSAMANECK, Y.J.; FURCHHEIM, N.; HEJNOL, A.; MARTINDALE, M.Q.*; LüTER, C.; Kewalo Marine Laboratory, Univ. of Hawaii; Museum Für Naturkunde, Berlin; Sars International Centre for Marine Molecular Biology; Kewalo Marine Laboratory, Univ. of Hawaii; Museum Für Naturkunde, Berlin mqmartin@hawaii.edu
Eyes in bilaterian metazoans are composed of either ciliary or rhabdomeric photoreceptors. Both receptor types exist throughout the Bilateria, but only vertebrates are thought to use ciliary photoreceptors for directional vision in cerebral eyes, while all other invertebrate bilaterians studied utilize rhabdomeric photoreceptors for this purpose. To test the hypothesis that protostome cerebral eyes employ exclusively rhabdomeric photoreceptors we investigated the larval eyes in the brachiopod Terebratalia transversa. We show that these pigment-cup eyes possess enlarged ciliary membranes for light perception, and express a c-opsin gene. Our results indicate that the dichotomy in the deployment of ciliary and rhabdomeric photoreceptors for directional vision is not as clear-cut as previously thought. The presence of ciliary photoreceptor based eyes in protostomes suggests that the transition between non-visual and visual functions of photoreceptors has been more evolutionarily labile than previously recognized and that co-option of cell types for sensory perception has occurred multiple times during animal evolution. We also observed expression of Terebratalia c-opsin in the presumptive anterior neuroectoderm, coincident with the positive phototactic behavior, in the absence of a discrete shading pigment or axonal connections between cells. Positive phototaxis in gastrula stage embryos suggests that a discrete shading pigment is not requisite for directional photoreception in metazoans. We propose that scanning photoreception mediating cell-autonomous changes of ciliary movement may represent an ancient mechanism for regulating locomotory behavior.
