Creature Feature: Mimic octopus

An animal that can seamlessly shift between hue, structure, and form seems impossible. This perfect shapeshifter, capable of blending into the background or “becoming” another animal at will, is the kind of thing conjured up in comic book writer’s imagination. Amazingly, a real life example of such a creature inhabits the depths of the ocean: the mimic octopus (Thaumoctopus mimicus).

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Mimic octopus (Thaumoctopus mimicus) are found in Indo-Pacific waters and were first discovered in 1998. [Source]
Many people are familiar with the camouflage abilities of the octopus. Used both as a defense mechanism against predators as well as a way to catch their prey, octopuses can change both the color of their skin and its texture. They are able to do this through neuromuscular mechanisms that control their chromatophores—which are pigment-producing cells—and through contraction of muscle bundles that change the texture of their skin.1 The mimic octopus, however, takes it a step further.

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Cephalopods have specialized cells called chromatophores which contain vacuoles filled with pigment. Nerve endings and musculature control whether these vacuoles are constricted or relaxed.; when expanded, the skin surface appears darker. [Source]
This elusive creature has mostly been spotted by scientists off the coast of Sulawesi in Indonesia. However, in 2012 one was found on the Great Barrier Reef. These animals occupy shallow waters in often muddy, silty areas. They are diurnal, i.e. active during the day, and spend most of their time foraging for food. These creatures eat mostly crustaceans and small fish and like other octopuses, they move using jet propulsion.2

However, the mimic octopus is unique among other octopuses because it not only changes its color and texture but also can completely replicate the appearance of other species. They have been found to mimic species such as flounders, venomous fish, snakes, tunicates, and sponges.2, 3 When mimicking a flounder, for example, they draw their tentacles in towards their center to form the body. While moving, they wave their arms to mimic flounder fin movements and position their eyes so that they protrude upward to maintain the proper eye position of this fish. These animals are such perfect replicas of their models that they even swim at the same speed.3

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The mimic octopus(Thaumoctopus mimicus) is a master disguise artist and often adopts the form, shape, and color of local organisms found in its habitat, including for example, flounders, lionfish, and banded sea snakes. [Source]
Another biological aspect that makes this creature so fascinating is that it changes color both to camouflage itself and to stand out. Check out this video of a mimic octopus modulating its skin surface color. This octopus is able to shift extraordinarily quickly between different colorations and will often take a striking brown and white striped pattern. Scientists think this could be a form of Batesian mimicry. Batesian mimicry is where an animal takes the appearance or coloration of a toxic organism in order to fool a predator into thinking that it is also toxic. In the above example, the octopus could be trying to fool a predator into thinking it is a toxic flounder.However, this hypothesis requires a bit more support because researchers do not know if the flounder species that the mimic octopus is copying are actually toxic.3

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Mimic octopus behavioral adaptation may be a form of Batesian mimcry, whereby they assume the pattern of toxic species to avoid predation. However, this hypothesis has yet to be empirically tested, as scientists must first determine the toxicity of the mimicked model species. [Source]
To examine this amazing mimicry behavior in depth, scientists analyzed the genomes of many octopus species to figure out when in evolutionary time the unique traits of the mimic octopus evolved. They discovered that the ability to change rapidly between different colors arose first in the lineage, followed by the long, flexible arms that allow the octopus to transform itself, and finally the capacity to use both the flashy coloration and shape-shifting behaviors at the same time. This suggests that having ostentatious coloration is beneficial to the octopus as a behavioral and physiological strategy to trick predators in.4

There is still a lot more to discover about the mimic octopus and the many species it mimics, including the locally-abundant flounders that are often found in the same habitats.3 This amazing creature employs many strategies to fool predators and prey, but we still do not know specifics about why the octopus uses these methods. This is can be attributed to the fact that we have not yet identified their predators or determined if these techniques are successful. There is also the fact that this species is found in a region in which far less research has been conducted. However, scientists are working to understand the evolutionary mechanisms that maintain and selected for these adaptations, which will provide further insight into the amazing behavior of these shape-shifting organisms.

[By: Elizabeth Berry] 

Elizabeth Berry is a 3rd year Wildlife, Fish, and Conservation Biology undergraduate student at UC Davis


References:

1Amodio, P, Fiorito G (2013) Observational and other types of learning in octopus. Handbook of Behavioral Neuroscience 22: 293-302.

2Coker, DJ (2012) Documentation of the mimic octopus Thaumoctopus mimicus in the Great Barrier Reef, Australia. Marine Biodiversity Records 6.

3Hanlon, RT, Conroy, LA, Forsythe, JW (2008) Mimicry and foraging behavior of two tropical sand-flat octopus species off North Sulawesi, Indonesia. Biological Journal of the Linnean Society 93(1): 23-38.

4Baker, B (2010) Unusual adaptations: evolution of the mimic octopus. BioScience 60(11): 962.

Additional references:

“How octopuses and squids change color” (Smithsonian Ocean Portal) http://ocean.si.edu/ocean-news/how-octopuses-and-squids-change-color

Main featured image [Source]

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