A pair of biologists at Walla Walla University, in the U.S., have developed a way to calculate the energy costs for certain types of animals with color-changing abilities. In their study published in the Proceedings of the National Academy of Sciences, Sofie Sonner and Kirt Onthank measured oxygen consumption rates for multiple octopuses during color changes.
Many creatures are known to change color, whether for camouflage, communication, regulating body heat or protection from the sun. Color changes can also occur quickly, as is the case with chameleons, tree frogs or octopuses, or slowly, such as with snow hares or many types of birds.
In this new study, the researchers wondered if animals that change color quickly pay a price for it metabolically. To find out, they captured several ruby octopuses and tested them to see how much energy they expended when changing colors.
The researchers tested 17 octopuses, before, during and after they changed color. Metabolic testing was done by collecting skin samples and placing them under a flashing blue light—this revealed the creatures’ chromatophores, which are pigment-bearing cells. Changing color involves expanding and contracting such cells.
They also customized a respirometer to measure the amount of oxygen being used by the cells as they expanded and contracted. Together, the two measurements allowed the researchers to gain reasonable approximations of energy expenditures during color changes.
The researchers found that the average octopus uses 219 micromoles of oxygen per hour when fully changing color. They note that such a high measurement shows that an octopus spends as much energy on changing color as it does for all the rest of its body functions when at rest.
The researchers suggest that the high energy cost of changing color may explain why octopuses spend so much of their time hiding in their dens—this allows them to capture passing prey while avoiding expensive color changes.
More information:
Sofie C. Sonner et al, High energetic cost of color change in octopuses, Proceedings of the National Academy of Sciences (2024). DOI: 10.1073/pnas.2408386121
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Calculating the energy costs of color changing in ruby octopuses (2024, November 19)
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