Cuttlefish could be the first animals shown to learn visually before birth or hatching, researchers say.
Cuttlefish embryos that develop in their translucent eggs with crabs nearby hatch into youngsters with a distinct preference for eating crabs, says Ludovic Dickel of the University of Caen in France. Without that pre-hatch view of crabs, the little cuttlefish attack shrimp in preference to crabs, he and his colleagues report in the July Animal Behaviour.
The preference develops from sight alone, Dickel says. The researchers kept the crabs in containers that prevented crab scents from getting into the water with the eggs.
Earlier work by the cuttlefish team showed that within a few hours of hatching, the babies need only one good look at crabs to develop a preference for them. Now the window of learning seems to be open even before hatching, Dickel says.
Other research teams have demonstrated that embryos start learning scents and sounds, Dickel says. Laughing gull chicks respond readily to parental crooning if they heard the sound repeatedly while still in the egg; and ants base their sense of who’s a nestmate on smells they experienced as larvae.
Cuttlefish offered a chance to test for visual learning because of their remarkable embryo eyes and the translucence of the egg coverings. When the mother lays the eggs, the view is obscured by the black cuttlefish ink. As the eggs approach the time of hatching, they swell to the point where the embryos can see through the translucent outer covering.
This test provides the first demonstration in any animal that embryos can learn the sights around them, says Dickel.
“In the world in general, I think visual learning in embryos is surprising and cool,” said Karen Warkentin of BostonUniversity, when she heard about the work. She studies defense reactions of frog embryos. “To me,” she added, “I don’t think it is so surprising — in that I’m used to frog embryos being able to do more than most people expect.”