This article is reposted from the old WordPress incarnation of Not Exactly Rocket Science.
The best communicators know to cater to their audiences, and cuttlefish are no different. A new study shows that these intelligent invertebrates can target their defensive signals to the hunting styles of different predators.
Cuttlefish and their relatives, the octopuses and squid, are expert communicators whose incredible skins can produce a massive range of colours and patterns. Cuttlefish mostly use these abilities to blend into the background but they can also startle and intimidate predators by rapidly changing the display on their dynamic skins.
Keri Langridge and colleagues from the University of Sussex, watched young cuttlefish as they were threatened by three very different predators – juvenile seabass, dogfish (a type of shark) and crabs. A glass partition protected the cuttlefish from any actual harm but gave them full view of the incoming threats.
She found that the cuttlefish only ever used startling visual displays when they were faced by seabass, which hunt by sight. As the fish approached, the young cuttlefish suddenly flattened their bodies to make themselves look bigger and flashed two dark eye-spots on their backs to startle the predator. This pattern is called a ‘deimatic display’ and it was used in 92% of encounters with seabass.
In contrast, Langridge found that the cuttlefish never presented the deimatic display, or any other type of visual signals, to dogfish and crabs in any of 72 trials. And for good reason – neither predator hunts by sight. Crabs sense chemicals in the water, while dogfish (like all sharks) track their prey through the electricity generated by their own bodies.
To these hunters, the cuttlefish’s dynamic skin is all but useless, and it would be foolish to waste time in bluffing with visual signals. That would just allow the predator to draw closer and might even attract the attention of other threats. Better then to immediately flee, which is what the young cuttlefish did.
Langridge found that young cuttlefish go through a similar series of threat displays for all three predators. They break their camouflage by first intensifying their colours and then turning uniformly dark. They then either used the deimatic display or fled immediately, depending on the species of predator.
The study begs the question: how do the cuttlefish tell the difference between the different predators? Even though the trained biologist’s eye could tell apart a dogfish and a seabass, they are superficially very similar. The remarkable consistency of the cuttlefishes’ responses suggests that they have access to clear clues that allow them to quickly and accurately distinguish between these groups.
Many of other cases of predator-specific signals come from the world of back-boned animals and I blogged about one such example earlier this year. Ground squirrels pump hot blood into their tails to make themselves look bigger in front of rattlesnakes, which hunt with by tracking body heat. However, they didn’t bother with hot tails when faced with gopher snakes, which lack heat-sensitive pits.
Langridge’s study is further evidence that the intelligence of cuttlefish and their kin is a match for many back-boned animals. Indeed, one of the cuttlefish’s relatives, the mimic octopus, also uses targeted defences. It changes both shape and colour to mimic a large variety of toxic marine animals and it tends to reserve its sea snake disguise when pestered damselfish, which sea snakes eat.
References: Langridge, K.V., Broom, M., Osorio, D. (2007). Selective signalling by cuttlefish to predators. . Current Biology, 17(24), R1044-R1045.