Octopuses do an amazing job of blending into their environments: they can match the objects they mimic in terms of colour, texture, pattern and brightness. A new study, which will be published in the Journal of Experimental Biology, has shown how even more remarkable they are: their responses to light are so much more interesting than initially thought.
Two-spot octopus (Octopus bimaculoides). Photo credits: Nathan Rupert/flickr CC BY-NC-ND 2.0
Researchers from the University of California have discovered that the two-spot octopus (Octopus bimaculoides) can detect light by its skin. Furthermore, light sensing does not involve the central nervous system (CNA).
When light was made to shine on the skin of the octopus, the cells containing the pigments, known as chromatophores, became enlarged, thereby giving the tissue colour.
“Even though chromatophores often change quickly, I was surprised at how quickly and dramatically the chromatophores respond to light with no input from the brain,” Todd Oakley, one of the authors said in a statement.
It was found that the skin made rhodopsin, a light-sensing protein. The latter is usually found in the eye, which can differentiate between light and dark.
Its skin was exposed to different light conditions. Different light colours would generate varying responses from the skin. For instance, no reaction was observed when the skin was exposed to red light, but it would dramatically change under blue light.
The following gif shows how the colour of the skin changes. It demonstrates how there is not response under red light, but when white light is directed to it, the chromatophores expand, and give it colour: from yellow to darker.
When exposed to light, the octopus skin changes colour. Photo credits: Todd Oakley/UCSB.
The researchers believe that the rhodopsin is linked to the chromatophores, and not to the CNS.
This research marks the first time that the skin’s response to light has been proven. However, its use is not yet determined.
“We do not know whether or not there is a beneficial function,” explained Oakley.