Cephalopods are among the most intelligent of marine life. Their highly advanced nervous systems allow them to exhibit a complex array of behaviors (for example, camouflage). Within this array is a rather unique behavior observed in the cuttlefish Sepia pharaonis. These elegant beings are now known to… intensely flap their arms? These animals are truly graceful.
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| A lovely photo of S. pharaonis. Image by Silke Baron at Wikimedia Commons. |
Researchers Kohei Okamoto, Haruhiko Yasumuro, Akira Mori, and Yuzuru Ikeda of the University of the Ryukyus in Okinawa, Japan observed this behavior on two separate occasions while studying S. pharaonis. The scientists had initially collected these cuttlefish with the intention of conducting other experiments but noticed this behavior while the cuttlefish were introduced to a large water-filled tank and while hunting prey. After noticing this wild arm-flapping behavior, the researchers turned their attention towards why the behavior was being displayed.
The researchers first observed this behavior in December of 2011. The cuttlefish were placed in a large, circular tank for conducting other experiments when a couple of them were observed to flap their arms. After the initial experiments were finished, a few of the cuttlefish were placed in the same sized tank and observations were recorded with a video camera over a period of five days. This behavior was revisited in 2013 for further observation. The cuttlefish they used were reared from eggs found in the same coastal waters of Okinawajima Island as the cuttlefish that were part of the 2011 experiments. Again, cuttlefish were placed in a large tank to observe the behavior with a video camera. The researchers counted each occurrence of the behavior and recorded the duration of each behavior. After observations were complete, the researchers performed experiments to observe the hunting ability of S. pharaonis. This arm-flapping behavior was observed unexpectedly while the cuttlefish hunted prey. The means of recording the behavior were the same as described above. In addition, the researchers recorded the number of prey caught between cuttlefish that did and did not display the behavior.
The researchers noticed variation in the frequency and duration of this behavior in the presence and absence of prey. When placed in a tank without prey, only a small number of cuttlefishes displayed this behavior. Of the cuttlefish that did flap their arms, the behavior lasted (on average) no longer than 37 seconds. However, the cuttlefish that were placed in a tank with prey, the behavior was displayed for at significantly longer period of time. In addition to that, more cuttlefish overall were seen flapping their arms in this second experiment. The cuttlefish that flapped their arms caught a significantly larger number of fish than the ones that did not flap their arms, despite being observed in the same tank and having access to the same number of prey animals. This observation led the researchers to believe that something about this unique behavior is helping the cuttlefish capture more prey.
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| A front view of a cuttlefish. Image by Stickpen at Wikimedia Commons. |
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| The resemblance is uncanny! Image by Maximilian Paradiz at Wikimedia Commons. |
What could this all mean? The researchers think that the cuttlefish may be mimicking another organism, specifically the hermit crab, to confuse the prey fish into thinking that they are another harmless animal. It is thought that the head of the cuttlefish resembles the shell of the hermit crab while the arms resemble the eyes and legs of the hermit crab. Posing as a harmless crab would allow the cuttlefish to get behind enemy lines and ultimately catch more prey. Further research will have to be done in lab as well as the field to see if this behavior is really that of mimicry. Other cephalopods are notorious for mimicking other animals, so it is not out of the realm of possibility. Studying this behavior would allow scientists to difurtveher into the evolutionary history of S. pharaonis. Until then, the graceful limb-flailing will remain an ever-tantalizing mystery.
References
Okamoto, K., Yasumuro, H., Mori, A., & Ikeda, Y., (2017). Unique arm-flapping behavior of the pharaoh cuttlefish, Sepia pharaonic: putative mimicry of a hermit crab. Journal of Ethology, 35(3), 307-311. DOI: 10.1007/s10164-017-0519-7
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