Cuttlefish not only wield three hearts and a 360-degree field of vision, but also a strong sense of self-control, suggests a new study.
As research from the Marine Biological Laboratory shows, when presented with the option of eating a raw king prawn immediately or a grass shrimp (their preferred food) after a short delay, the marine molluscs chose the latter option.
In fact, while all six cuttlefish tested could tolerate a delay in feeding of 15 seconds, some could extend this to 130 seconds. These results indicate the cephalopods can delay gratification similar to large-brained vertebrates such as chimpanzees.
The cuttlefish that could wait longer before eating its favourite food also performed better in a cognitive test, learning faster to associate a visual cue with a food reward.
If this experiment sounds familiar, it’s because it’s an adapted version of the famous Stanford marshmallow test, which gave children the chance of chomping on an immediate reward (one marshmallow) or a better but delayed treat (two marshmallows).
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However, while it’s relatively easy to explain the marshmallow test to human participants, communicating the idea to cuttlefish was more complex.
At first, the invertebrates were placed in an aquarium leading to two chambers marked with one of three symbols representing immediate gratification, delayed gratification and ‘inaccessible’. To help them learn the concepts required, the same type of food was added to each chamber. After the cuttlefish had made its ‘choice’ of prey, the other food was immediately removed.
This meant, after time, the cuttlefish appeared to understand that different chambers had unique rules, meaning researchers could use different treats in the actual experiment.
As lead researcher Dr Alexandra Schnell explained, the cuttlefish’s sense of self-control is evident in its natural environment: “Cuttlefish spend most of their time camouflaging, sitting and waiting, punctuated by brief periods of foraging.
“They break camouflage when they forage, so they are exposed to every predator in the ocean that wants to eat them. We speculate that delayed gratification may have evolved as a by-product of this, so the cuttlefish can optimize foraging by waiting to choose better quality food.”
Usually found in tropical and temperate oceans, cuttlefish have one of the largest brain-to-body ratios of all invertebrates. The cephalopod can also change its skin’s appearance in less than a second to blend into its background.
Reader Q&A: How many hearts does an octopus have?
Asked by: Louise Denver, Southampton
Octopuses have three hearts: one pumps blood around the body; the other two pump blood to the gills. The reason for this impressive cardiac hardware probably comes down to the unusual composition of their blood.
Unlike vertebrates that have iron-rich haemoglobin packed into red blood cells, octopuses – along with some tarantulas, scorpions and horseshoe crabs – have copper-rich haemocyanin dissolved directly in their blood (this means their blood is blue!).
Haemocyanin is less efficient than haemoglobin as an oxygen transporter. The three hearts help to compensate for this by pumping blood at higher pressure around the body to supply the octopuses’ active lifestyle.
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