For several years now, biologists have theorized that some fast-changing animals, such as Lachnolaimus maximus, do not just do it with their eyes. They thought that the skin played a role, but could not yet explain it.
In a new study, Biologists Lori Schweikert and Sönke Johnsen of Duke University have shown that light detection has evolved separately in both tissue types (in the eye and skin) in hogfish.
According to them, the phenomenon of dermal photorception does not allow animals to perceive all the details of their environment as is the case with their eyes. It nonetheless allows them to be sensitive to changes in brightness or wavelength, such as moving shadows projected by predators or fluctuations in light associated with different periods of the day.
The hogfish lives in the shallow waters and coral reefs of the western Atlantic, from Nova Scotia to Canada to northern South America.
Its skin can become beige when it is in the sandy bottom of the ocean to hide from predators or ambush prey. It can also sport a bright and contrasting pattern to attract a partner or threaten an opponent.
The key to these transformations is cells called chromophores that contain pigments and that, when activated by light, can spread or group themselves to change the color or pattern of the skin.
In their work, the researchers took pieces of skin and retina from a female hogfish captured in Florida and analyzed the DNA to find out which genes were activated in each tissue.
Previous studies suggested that in other animals that change colors such as octopuses, the same molecular pathway can detect light in the eyes and through the skin.
This is not the case, however, in hogfish, since virtually none of the genes involved in the detection of light in the retina of the eyes is activated in the skin.
The results show that an alternative pathway allows the skin to perceive light, resulting in a molecular chain reaction.
The link between the cutaneous vision and the vision of the eyes that leads to a change in the appearance of the fish remains however unknown.
Light-sensitive skin may provide information on some features that are beyond the animal’s field of vision or are outside the range of wavelengths that the eye can capture.
In any case, these results show that fish have found a way to “see with their skin and change color quickly,” says Schweikert.
The details of this work are published in the Journal of Comparative Physiology.