In the eyes of mantis shrimp, certain molecules can switch from one state to another when exposed to two different colors of light.
These marine animals, also known as stomatopods, are famous for their limbs, which can strike incredibly fast. But their eyes are just as astonishing. While we use three main types of receptors to distinguish colors, some mantis shrimp have many more light-sensitive pigments.
Photograph of a colorful stomatopod (Odontodactylus scyllarus), a mantis shrimp with highly developed compound eyes.
Photo: prilfish, via Wikimedia Commons.
Researchers from the University of Liège and Humboldt University of Berlin studied 17 of these pigments, found in a specialized band of the animals’ eyes. These small proteins capture certain colors and allow visual cells to transmit a nerve signal. The team wanted to understand how each one responds to light.
Four pigments revealed a particularly interesting property: they function like reversible switches. Two are activated by red light, then returned to their initial state by blue light. The other two respond to blue and can be reset with orange light.
Our own visual pigments do not work quite this way. In humans, after capturing light, they need to undergo a series of chemical transformations to return to their initial state. In these shrimp, some pigments can return directly to that state thanks to a second color of light.
The researchers also identified pigments that are highly sensitive to red hues, down to wavelengths close to the limit of human vision. Colored filters present in mantis shrimp eyes further expand their ability to receive light. But having many pigments does not necessarily mean distinguishing colors more finely than we do.
What exactly are these switches used for in the animal’s life? They could help its eyes function under very different lighting conditions, in broad daylight or as the light fades. To find out, researchers will need to observe how shrimp actually use these abilities to find food or detect danger.
This discovery also interests medicine and biological research. Scientists already use light to activate certain cells in the laboratory. These pigments could one day provide new ways to control them, with one color used to activate a signal and another to stop it.
These applications do not yet exist, however. For now, the team has mainly revealed the astonishing behavior of natural proteins that, in the eyes of small crustaceans, act almost like miniature switches.