Ruby octopuses (Octopus rubescens) were used as a model species to analyze the energetic costs of color change. (Photo courtesy of Megan Mindlin)
Octopuses burn about the same number of calories changing colors as a person would burn during a 30-minute jog, according to new research.
Octopuses are masters of camouflage, changing color instantly to ward off predators and hide from their prey. However, the energy costs associated with this color change remain a mystery.
Now, for the first time, biologists have been able to measure how much energy these creatures actually expend to perform their complete color changes. The discovery could give scientists more insight into the biology of these animals.
“All adaptations in the animal kingdom have advantages and disadvantages,” senior study author Kirt Onthank, a marine biologist and professor of biology at Walla Walla University in Washington, told Live Science. “We know a lot about the advantages of the octopus’ color-changing system, but until now, almost nothing was known about its costs. Understanding the costs of octopus color-changing helps us better understand the trade-offs octopuses make to remain undetectable.”
Like many other cephalopods, octopuses have a special set of tiny organs on their skin known as chromatophores.
“Each chromatophore is a small elastic sac of pigment that has muscles attached to it, like the spokes of a wheel connecting to the hub,” Onthank explained. “When the muscles are relaxed, the sac contracts to a small point that is usually too small to see. When the muscles contract, they stretch this sac over a small area of skin, and the color inside becomes visible.”
Each of these chromatophores can be compared to a tiny pixel on a screen. “There are 230 chromatophores per square millimeter of octopus skin,” Onthank added. “For comparison, a 13-inch laptop monitor with 4K resolution has about 180 pixels per square millimeter.”
To change color, these pixelated organs contract thousands of tiny muscles. “By controlling each of these chromatophores with their nervous system, octopuses can create very complex and impressive camouflage or visual displays,” Onthank said.
In a new study published November 18 in the journal PNAS, Onthank and first author Sophie Sonner, who conducted the research as part of her master's thesis at Walla Walla University in Washington state, collected skin samples from 17 ruby octopuses (Octopus rubescens) and measured oxygen consumption during the expansion and contraction of their chromatophores. They then compared that data to each octopus's resting metabolic rate.
The results showed that the average octopus requires about 219 micromoles of oxygen per hour to fully change color – about the same amount of energy it uses to perform all other bodily functions at rest.
Onthank explained that if humans had the color-changing skin of an octopus, we would burn about 390 extra calories a day changing color—about the same as going for a 23-minute jog.
Octopuses and cephalopods aren’t the only creatures that can change color. “Rapid color change has evolved independently in multiple animal taxa, including amphibians, reptiles, fish, arthropods, and mollusks, highlighting its broad adaptive implications,” Sonner told Live Science.
However, cephalopods' color changes are much faster and more precise. “Most other animals that can change color quickly, like chameleons, use hormones to control the system and the pigments in their cells,” Onthank said. These methods are slower but likely require less energy, he added.
The researchers hope to apply their technique to
Sourse: www.livescience.com
