For most animals, life before birth is a dark experience. For example, humans are trapped in the womb for nine months, and even animals and birds that hatch from eggs don’t have much light reaching them. But now new research shows that cuttlefish may not be kept in the dark in the same way.
When cuttlefish eggs are laid, they’re stained black with ink. But as the embryos develops and grows, the egg becomes see-through. Intriguingly, by this point, the baby cuttlefish’s eyes are properly developed. So can they see they outside world from the comfort of their egg? New results from Anne-Sophie Darmaillacq and her team in France suggest they can, and that this might be vital for the cuttlefish to survive in the harsh world of the sea.
The researchers studied cuttlefish eggs laid in a tank, arranged in such a way that they were in view of another, separate tank before hatching. The team then put crabs into the other tank, or left it empty. This setup means that the cuttlefish aren’t exposed to any chemical signals from the crabs, but on vision alone.
Once the cuttlefish hatch, they sink to the bottom of their tank, and lose sight of the crabs next door. Then the researchers caught the baby cuttlefish, and gave them a choice of crabs or cuttlefish to eat. And they found that if the cuttlefish has ‘seen’ crabs while they were still in their eggs, they clearly preferred crabs for dinner.
This is the first time that researchers have ever found evidence that embryos can use visual information before they are born. But why might it be so important for cuttlefish? These animals depends very strongly on vision – for example, as they change colour, shape and patterning for defence or communication.
But they hatch alone, and have no help from their parents to tell them how to find food. So perhaps the baby cuttlefish are learning about their potential menu choices before they’re born, so they can get on with the business of feeding as fast as possible.