Picture above of Octopus bimaculoides hatchling with region showing peripheral sensory neurons. Courtesy of http://jeb.biologists.org/content/jexbio/218/10/1513.full.pdf
Can you imagine, if the human skins could “see” a threat and respond accordingly, while our backs were turned (No seeing with eyes or touching involved)? Eye-independent, light-activated chromatophore expansion (LACE) and phototransduction genes in the skins of cephalopods make this possible. This mind blowing feature of Octopus bimaculoides and other cephalopods is what I would like to discuss on this final blog.
When the skin of O. bimaculoides is exposed to bright white light, the chromatophores present react by expanding, a behavior termed LACE. LACE responses is evident that the skin of O. bimaculoides can sense light, independent of eyes.
Ramirez and Oakley hypothesized that r-opsin, a protein responsible for detecting light found in the eyes of octopuses may also be present in their skin, thus activation of light-sensitive chromatophore in their skin was possible, without the input of the eyes (Ramirez et al., 2014).
11 adult Octopus bimaculoides and their hatchlings were obtained, killed and their funnels dissected. Ten dissected funnels were mounted in fresh seawater filled Petri dishes using insect pins. The mounts were set up at equal distance from a white light fiber optic source and the reaction of the chromatophores on the skins was observed and recorded using infrared CCD camera. The photon counts and absolute radiance were measured with spectrophotometer. Three trials for the set ups were performed to ensure accuracy.
There have been a lot of behavioral and physiology research in relations to light sensitivity of mollusks skins (Ramirez et al., 2011). This specific research paper is the best evidence till date for cephalopods’ light-sensitive skin and the role of LACE in controlling chromatophore for camouflage, alongside the main control of the central nervous system.
Further studies to determine on the specific functions of opsin-expressing cells in hatchling O. bimaculoides skin and the extent of importance of the role of opsin in their function/functions apart from photoreception. The evolutionary path to LACE in the skins of octopuses is worth researching also.
REFERENCE
Ramirez, M. et al (2011). Understanding the dermal light sense in the context of integrative photoreceptor cell biology. Vis. Neurosci. 28, 265-279.
Ramirez M. D.& Oakley T. H. (2014) Eye-independent, light-activated chromatophore expansion (LACE) and expression of phototransduction genes in the skin of Octopus bimaculoides. Journal of Experimental Biology 2015, 218: 1513-1520; doi: 10.1242/jeb.110908 http://jeb.biologists.org/content/jexbio/218/10/1513.full.pdf
KEYWORDS
Chromatophore is a pigment-containing cell in the deeper layers of the skin of animals. The distribution of the chromatophores and the pigments determine the color patterns of an organism.
Mechanoreceptors are specialized neurons that transmit mechanical deformation information into electrical signals.
Phototransduction is the conversion of light into a change in the electrical potential across the cell membrane. This process involves the sequential activation of a series of signaling proteins, leading to the eventual opening or closing of ion channels in the photoreceptor cell membrane.
Visual phototransduction is the photochemical reaction that take place when light (photon) is converted to an electric signal in the retina.