Is there anything the octopus can’t do? They can solve puzzles, contort their bodies to mimic other animals and even use jets of water to expertly snipe bothersome aquarium lights. Speaking of lights, researchers from the University of California, Santa Barbara have found yet another amazing octopi superpower: They can “see” with their skin by sensing light. For octopi, eyes are so last millennium.
“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). “But it can sense an increase or change in light. Its skin is not detecting contrast and edge but rather brightness.”
The ability is even more remarkable considering the fact that the octopus has some of the sharpest eyes in the ocean, and certainly the best eyesight of any mollusk. Using their nearly human-quality eyes, they perceive their environment and send signals to the chromatophores in their skin, which allow them the change color.
However, the research by the UCSB team found that the octopus’ super-perceptive skin is, in a way, an extension of its eyes. The same light-sensitive proteins found in its eyes, called opsins are also found in its skin, which explains how the octopus is able to respond to changes in brightness, even when blinded optically. Ramirez named the phenomenon “Light-Activated Chromatophore Expansion,” or LACE.
For the experiment, took octopus tissue and bathed in in white light, upon which the pigment cells immediately expanded to change color. Since the tissue was not attached to the eyes or even brain, this suggests that the opsins themselves are directly connected to the chromatophores. Further experimentation found that the tissue responded most strongly to light in the blue wavelength. Doing so requires the protein rhodopsin, which is typically found in the eye.
The fact that the eye proteins appear to have made their way to the skin, combined with the increased sensitivity to blue light (the wavelength of most common exposure in the ocean), suggests that this ability to “see” with the skin is actually an evolutionary adaptation.
“It looks like the existing cellular mechanism for light detection in octopus eyes, which has been around for quite some time, has been co-opted for light sensing in the animal’s skin and used for LACE,” said Ramirez. “So instead of completely inventing new things, LACE puts parts together in new ways and combinations.”
Scientists know that other mollusks can sense light, but the next step will be to determine to what degree, if any, they can do so on the same level as octopi.