It has long been assumed that octopuses’ ability to change color had developed as an evolutionary trait to help them avoid detection by predators, although a new in-depth analysis of the behavioral responses to these changes of hue has revealed a rather different story. According to a new study in the journal Current Biology, some species of cephalopod may adjust their color in order to indicate their level of aggression towards rivals.
Researchers used underwater cameras to observe the behavior of a species called Octopus tetricus, and noted that their agonistic interactions tended to be mediated by changes in coloration, as well as other types of body language. As such, the study authors conclude that these displays have more of a communicative function than had previously been thought, thereby shattering the idea that octopuses are asocial.
In particular, they describe how darker colors were associated with increased aggressiveness. Accordingly, whenever two octopuses displaying a dark color approached one another, fights tended to break out, while lighter colored animals would retreat when confronted by darker ones.
The researchers also outlined what they describe as a “stand tall” pose, whereby octopuses spread their web of tentacles out and raise their mantle (body). Previous hypotheses have suggested that this behavior may represent an attempt to seek a higher vantage point in order to gain a better view of incoming predators or prey. However, the study authors note that this body position does not actually elevate the eyes, and is therefore unlikely to serve this purpose.
Instead, they propose that this behavior is another form of signaling, designed to “enhance apparent size and increase conspicuousness.” This, they suggest, provides a means of communicating their strength to other octopuses in order to intimidate them.
Summing up their findings, the researchers claim that “we should no longer consider octopuses as solitary and asocial or their body pattern repertoires and behaviors as having evolved solely in the context of anti-predator camouflage.” Rather, more focus should now be placed on trying to decipher the various ways in which they communicate with one another via body language.
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