A species of octopus has been found to have the ability to sense light through its skin.
A new study has found that the skin of the California two-spot octopus, Octopus bimaculoides, can sense light even without input from the central nervous system. The animal does this by using the same family of light-sensitive proteins called opsins found in its eyes — a process not previously described for cephalopods.
"Octopus skin doesn’t sense light in the same amount of detail as the animal does when it uses its eyes and brain," said lead author Desmond Ramirez, a doctoral student in the Department of Ecology, Evolution and Marine Biology (EEMB) at University of California, Santa Barbara. "But it can sense an increase or change in light. Its skin is not detecting contrast and edge but rather brightness."
In order to record the skin’s sensitivity across the spectrum, Ramirez exposed octopus skin to different wavelengths of light from violet to orange and found that chromatophore response time was quickest under blue light. Molecular experiments to determine which proteins were expressed in the skin followed. Ramirez found rhodopsin — usually produced in the eye — in the sensory neurons on the tissue’s surface.
According to co-author Todd Oakley, this new research suggests an evolutionary adaptation. "We’ve discovered new components of this really complex behaviour of octopus camouflage," said Oakley, who calls cephalopods the rock stars of the invertebrate world.
Octopuses are not the only marine mollusks whose skin can sense light, but scientists don’t know yet whether the skin of those other animals contains the light-sensitive opsins. If they do, Ramirez wants to understand how these two groups are related. "Do they all come from the same ancestral source or did they evolve multiple times?" he asked. "What kind of behaviours do the different groups share and what kind of behaviorus does the skin sensing light underlie?”
Ramirez and Oakley are conducting new experiments that will seek to answer those questions and more.
The researchers’ findings appear in the Journal of Experimental Biology.
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