Octopuses are renowned for their exceptional camouflage abilities, seamlessly blending into their surroundings with remarkable speed and precision. They can transform themselves into near-perfect imitations of coral, rocks, or even other marine species, a feat that has captivated scientists and the public alike. However, new research suggests this extraordinary talent comes at a significant metabolic cost.
Biologists Sofie Sonner and Kirt Onthank of Walla Walla University in the US, published their findings in the *Proceedings of the National Academy of Sciences*, revealing the surprisingly high energy demands of an octopus's colour-changing mechanism. Their study indicates that the process of changing colour is exceptionally energy-intensive, potentially representing one of the most metabolically expensive forms of colour change in the entire animal kingdom. This is primarily due to the complex interplay of the nervous and muscular systems involved in controlling the chromatophores â the pigmented cells responsible for the colour changes.
Many animals exhibit colour change, utilising it for communication, thermoregulation, or camouflage. Active camouflage, as seen in cephalopods like octopuses and chameleons, requires significant energy expenditure. While effective, the precise energetic cost of this strategy in octopuses has remained relatively unclear until now.
Sonner and Onthank's research involved studying skin samples from the East Pacific red octopus (*Octopus rubescens*). These samples, rich in chromatophores, were exposed to blue light in a laboratory setting, triggering chromatophore activation. By monitoring the oxygen consumption of the samples both in their inactive and activated states, the researchers were able to quantify the energy expenditure associated with colour change.
Extrapolating these findings to the entire surface area of a ruby octopus, they calculated the total energy required for complete chromatophore activation. Remarkably, this energy expenditure proved to be almost equivalent to the energy consumed by the rest of the octopus's body at rest. When factoring in other energy-consuming activities, such as altering skin texture to mimic various substrates and the neural processing involved in controlling the colour change, the overall metabolic cost becomes even more substantial.
This high energetic cost offers a potential explanation for several observed behaviours in octopuses. The prevalence of nocturnal lifestyles in some species could be a strategy to minimise the need for camouflage in darkness. However, species like the ruby octopus are diurnal, highlighting other adaptive strategies. The researchers suggest the frequent use of dens and hidey-holes by many octopus species could serve as an energy-saving mechanism, reducing the need for constant camouflage and thereby lowering metabolic expenditure. While hidden in their dens, octopuses are protected from predators and don't actively hunt, minimizing the need to employ their chromatophore system extensively.
The study's findings shed new light on the evolutionary pressures shaping octopus behaviour and physiology. The remarkable camouflage ability, while undeniably advantageous, necessitates a substantial energetic investment, prompting octopuses to employ additional strategies, such as seeking shelter, to conserve energy and enhance survival. The research underscores the complex interplay between energetic constraints and adaptive strategies in the natural world, challenging our understanding of the seemingly effortless mastery of camouflage displayed by these fascinating creatures.