While two other species of octopuses are known to imitate flounder, this is the first report of flounder mimicry by an Atlantic octopus, and only the fourth convincing case of mimicry in cephalopods.
The study was published this week in Biological Bulletin.
Comparing still photographs and video footage from five Caribbean locations collected over the last decade, researchers observed uncanny similarities between the small and delicate octopus and the peacock flounder, Bothus lunatus, one of the most common sand dwellers in the Caribbean. They compared not only coloration, which in each animal resembled the sandy seafloor, but swimming speed and form.
Macrotritopus defilippi swimming forward and mimicking the shape, speed, and behavior of flounder swimming. Photo by R. Hanlon
Just like flounder, the octopuses contoured their bodies to hug the wavy seafloor, tapering their arms behind them. They also swam with the same fits and starts as flounder at the same speeds. Interestingly, the octopuses mimicked flounder only when swimming, when movement would compromise their camouflage. How well the animals blended in with their background differed. The octopus showed more highly controlled and rapid skin patterning than the flounder, whose camouflage was slower and less precise.
"We were equally impressed with the remarkable camouflage of this small octopus species even when it was stationary yet entirely exposed on top of the open sand," says Hanlon. "The apparent match in pattern, color, brightness, and even 3-dimensional skin texture was noteworthy even when compared to other changeable cephalopods. They also demonstrated an unusual form of disruptive camouflage."
So why do Atlantic longarm octopuses choose to imitate flounder as a way to avoid the threat of predators? More study of cephalopod mimicry is needed, but a possible explanation, according to Hanlon and his team, could be that predators who could easily take a bite out of the small, soft octopus might find a rigid flatfish like the flounder too much of a mouthful and avoid them.
Citation: Roger Hanlon, Anya C. Watson, Alexandra Barbosa, 'A mimic octopus: in the Atlantic: flatfish mimicry and camouflage by Macrotritopus defilippi', The Biological Bulletin, February 2010, 218, 15-24