M. Desmond Ramirez is currently a postdoctoral research associate at the University of Massachusetts Amherst. He uses the varied nervous systems of mollusks to understand how novel traits arise through evolution. His current work focuses on neuronal cell types in sea slugs.
“Skin-sight” shows local influence of body patterning in octopuses
Cephalopods are renowned for changing the color and pattern of their skin for both camouflage and communication. Yet we still do not understand all of the mechanisms that cephalopods use to control the pigmented chromatophore organs in their skin that change their body patterning. While such changes are thought to rely primarily on eyesight, we found that the skin of Octopus bimaculoides is intrinsically sensitive to light and that this dispersed light sense causes the chromatophores in excised skin to expand in response to bright white light. We call this behavior Light-Activated Chromatophore Expansion (or LACE). Octopus LACE is the clearest demonstration to date of eye-independent light sensing in the skin of cephalopods. To identify potential molecular mechanisms that may underlie LACE, we found that the same protein that senses light in octopus eyes, r-opsin, is also expressed in their skin, and we identified peripheral sensory neurons in the skin that express r-opsin. Experiments that shone different wavelengths of light on the skin suggested that the opsin in the skin is sensitive to the same part of the light spectrum as r-opsin in their eyes. LACE suggests that octopus skin is intrinsically sensitive to light and that this dispersed light sense may contribute to their unique and novel camouflage abilities. Taken together, these data suggest that a common molecular mechanism for light detection in eyes may underlie LACE and may have been co-opted during evolution for light sensing in octopus skin.