Hogfish Can ‘See’ with Its Skin

Researchers have long suspected that color-changing animals like hogfish (Lachnolaimus maximus) don’t just rely on their eyes to tune their appearance to their surroundings — they also sense light with their skin; but exactly how ‘skin vision’ works remains a mystery. Now, a new genetic analysis of the hogfish reveals evidence to explain how they do it. Published in the Journal of Comparative Physiology A, the results suggest that light-sensing evolved separately in two tissues.

The hogfish is a species of wrasse native to the western Atlantic Ocean. It is present in the Caribbean and north to Bermuda and the Carolinas and extends southwards to the northern region of the Brazilian Coast.

The species is found on coral reefs at 10-131 feet (3-40 m) depth, especially sandy outer reef slopes. Juveniles are most common in shallow seagrass, and inshore reef habitats.

The hogfish can make its skin whitish to blend in with the sandy bottom of the ocean floor and hide from predators or ambush prey. Or it can take on a bright, contrasting pattern to look threatening or attract a mate.

The key to these makeovers are special pigment-containing cells called chromatophores, which, when activated by light, can spread their pigments out or bunch them up to change the skin’s overall color or pattern.

“With ‘dermal photoreception,’ as it is called, the skin doesn’t enable animals to perceive details like they do with their eyes,” said study lead author Dr. Lori Schweikert, a postdoctoral scientist at Duke University.

“But it may be sensitive to changes in brightness or wavelength, such as moving shadows cast by approaching predators, or light fluctuations associated with different times of day.”

Dr. Schweikert and co-authors, Duke University’s Professor Sönke Johnsen and Dr. Bob Fitak, took pieces of skin and retina from a single female hogfish caught off the Florida Keys and analyzed all of its gene readouts, or RNA transcripts, to see which genes were switched on in each tissue.

Previous studies of other color-changing animals including octopuses and cuttlefish suggest the same molecular pathway that detects light in eyes may have been co-opted to sense light in the skin. But the study authors found that hogfish skin works differently.

Almost none of the genes involved in light detection in the hogfish’s eyes were activated in the skin. Instead, the data suggest that hogfish skin relies on an alternative molecular pathway to sense light, a chain reaction involving a molecule called cyclic AMP.

“Just how the hogfish’s ‘skin vision’ supplements input from the eyes to monitor light in their surroundings and bring about a color change remains unclear,” Dr. Schweikert said.

“Light-sensing skin could provide information about conditions beyond the animal’s field of view, or outside the range of wavelengths that the eye can pick up.”

“Together with previous studies, our results suggest that fish have found a new way to ‘see’ with their skin and change color quickly.

sci-news.com

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