Cuttlefish spot target prey early

By Matt Walker BBC

Embryos exposed to crabs preferred them as prey later in life

It's a bit like something out of the famous sci-fi horror movie Alien.

Before they have even hatched, cuttlefish embryos can peer out of their eggs and spot potential prey.

It is the first time any animal has been shown to learn visual images before they are born.

Ludovic Dickel and his colleagues at the University of Caen Basse-Normandy, France, made the discovery by placing crabs alongside cuttlefish eggs in a series of laboratory tanks.

Those embryos exposed to crabs preferred them as prey later in life, the scientists report in the journal Animal Behaviour.

The young embryos must be able to see through their translucent egg case, the scientists believe, and learn which animals are worth hunting even before they have hatched.

"This is the first time there is evidence of visual learning by embryos," said Dr Dickel.

Visual cues

Embryos are known to able to pick up chemical and auditory cues - unborn gulls, for example, learn to recognise the alarm calls of their parents whilst still in the egg, while salmon and frog embryos can learn the chemical signatures of the surrounding water before they hatch.

But until now, no one has looked at whether unborn animals can also learn visual images. Dickel and his team decided to study embryos of the cuttlefish Sepia officinalis, a relatively advanced ocean-going mollusc closely related to squid and octopus.

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They harvested wild eggs, and placed them in tanks filled with sea water.

Crabs, a common prey of adult cuttlefish, were also placed into the tanks, but enclosed in separate compartments. Crucially, the compartment sides were made of clear glass, so the crabs were in plain view of the eggs.

But the embryos could not smell or hear the crabs. Once the cuttlefish embryos hatched, they were instantly moved, to ensure they could not glimpse the crabs, and were not exposed to any other prey until they were seven days old.

They were then set free in a lab tank full crabs and shrimp, another cuttlefish delicacy.

'Window of genius'

Remarkably, cuttlefish embryos not exposed to crabs preferred to hunt shrimp once they were born.

But those embryos exposed to crabs much preferred to hunt crabs after hatching. And the clearer the view of the crabs they were given, the greater their taste for it.

Dickel says that his team has recently discovered that extremely young cuttlefish have very good memories and are capable of astonishing feats of learning, despite their young age and tiny, immature brains.

But this "window of genius", as he puts it, appears to open even before hatching.

Usually, cuttlefish eggs lie in an envelope full of black ink. But this clears as the embryos grow older, leaving them growing within translucent eggs.

These unborn cuttlefish also have fully developed eyes. That leads the researchers to conclude that the cuttlefish embryos must peer through their eggs, and learn to recognise their prey, a behaviour which will help give them a head-start in life.

It is less likely that birds, reptiles and, particularly, mammals - including humans - could recognise visual images in the womb.

But the cuttlefish discovery helps reinforce the idea that some animals at least can begin to learn before they are born.

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