| Animal photoreceptors in eyes and other tissues typically use visual pigments, composed of a chromophore bound to an opsin transmembrane protein, to detect light. Dozens of opsins are expressed in the eyes of some species of stomatopod crustaceans, or mantis shrimps. Despite the atypically complex visual systems of mantis shrimps, photosensitivity had not been studied in nonocular mantis shrimp tissues. The presence and complexity of extraocular photoreception in mantis shrimps may help us to make inferences about the evolutionary history and function of animal opsins and photoreceptors.;My dissertation research has investigated extraocular photoreception in mantis shrimps using a multidisciplinary approach. My transcriptomic analyses revealed that four opsin transcripts are abundantly expressed in the cerebral ganglion (CG), or brain, of a Caribbean mantis shrimp species (Neogonodactylus oerstedii). My phylogenetic reconstructions indicate that one of the four opsins shares sequence similarities with middle-wavelength-sensitive (MWS) crustacean opsins, and the other three with long-wavelength-sensitive (LWS) crustacean opsins. I then visualized the distinct patterns of opsin expression in the optic lobes, ventral eye, and CG of N. oerstedii by in situ labeling using probes based on the four opsin transcripts. In the optic lobes, I found that the MWS opsin gene is broadly expressed around several major neuropils: the lamina, medulla, lobula, and hemiellipsoid body. In the cerebral ventral eye (common among crustaceans), I observed that the MWS opsin gene and one LWS opsin gene are both expressed. The other two LWS opsin genes are expressed within the olfactory lobes of the CG and in large cell bodies that are densely clustered. In the same mantis shrimp species, I found that the illumination of blinded individuals elicits behaviors akin to crayfish escape responses (tail-flipping, walking, and swimming), showing that illumination of extraocular photoreceptors is sufficient to produce photolocomotory responses. My electrophysiological recordings reveal that the ventral eye produces electrical responses to illumination. However, the distinct patterns of opsin expression imply that extraocular photoreceptors contribute to mantis shrimp physiology in several ways and require further investigation. I also confirmed the presence of a ventral eye and visualized extraocular opsin expression in a mantis shrimp species with simpler, derived eyes (Squilla empusa), suggesting that extraocular photoreception is common among mantis shrimp species. There is certainly much more to discover about how mantis shrimps sense the world. |
