Octopuses are fascinating creatures capable of instantly changing the color of their skin. Until today, the extent of the energetic effort required by this phenomenon in cephalopods was unknown. The study, published in the journal PNAS, provided valuable data, and the results are astonishing.
Chromatophores: the key to color change
Chromatophores are organs found in the skin of octopuses, responsible for their incredible ability to change color. Kirt Onthank, biologist and main author of the study, describes in the columns of LiveScience a chromatophore as being “a small expandable bag of pigment to which spokes of muscle are attached, like the spokes of a wheel attached to the hub”.
It is the opening of these bags that reveals the different colors. The professor of biology at the University of Walla Walla explains that “the muscles contract, the pigment sac unfolds, and the color it contains becomes visible to the naked eye. When the muscles relax, the pigment is contained in a small, almost invisible dot”.
This mechanism is very efficient and allows the octopuses to change color almost instantly. Each square millimeter of an octopus' skin is covered in 230 chromatophores, which it can control simultaneously. A process that allows octopuses to “create very elaborate and impressive camouflages or displays”says Kirt Onthank.
An effort comparable to running
In order to measure the amount of energy required for color change, the team of researchers observed the skin samples of seventeen ruby octopuses (Octopus rubescens)a red species found in the eastern Pacific.
The scientists measured oxygen consumption to assess the energy deployed during the activation of the chromatophores. They found that octopuses use 219 micromoles of oxygen per hour to change color. This is almost as much as the amount of oxygen needed to maintain their vital functions when they are at rest.
Subsequently, these results were compared with human energy needs, and the numbers are surprising. If we owned an octopus skin, our body would burn around 390 extra calories per day. That's the equivalent of a 23-minute race.
An impressive feat but essential to their survival
For the co-author of the research, Sofie Sonner, octopuses are not the only ones capable of achieving this feat: “Rapid color change has evolved independently multiple times in a wide range of animal taxa, including amphibians, reptiles, fish, arthropods and molluscs.”
Many animals can achieve this, but remain less efficient than cephalopods: “These methods are slower but probably also consume less energy,” shade Kirt Onthank.
Although the energy required for this process is considerable, it is essential to their way of life. Octopuses do not have a shell to protect them. On the other hand, their ability to change color allows them to compensate for this lack of physical protection. Indeed, their ability to blend into the environment or adopt threatening colors allows them to survive in a marine world full of predators.
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