How the color-changing hogfish 'sees' with its skin

March 12, 2018 by Robin A. Smith, Duke University
A pointy-snouted reef fish called the hogfish can change from white to spotted brown to reddish depending on its surroundings. Credit: Dean Kimberly and Lori Schweikert

Some animals are quick-change artists. Take the hogfish, a pointy-snouted reef fish that can go from pearly white to mottled brown to reddish in a matter of milliseconds as it adjusts to shifting conditions on the ocean floor.

Scientists have long suspected that animals with quick-changing colors 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, genetic analysis of hogfish reveals new evidence to explain how they do it. In a new study, Duke University researchers show that hogfish skin senses light differently from eyes.

The results suggest that light-sensing evolved separately in the two tissues, said Lori Schweikert, a postdoctoral scholar with Sönke Johnsen, biology professor at Duke.

With "dermal photoreception," as it is called, the skin doesn't enable animals to perceive details like they do with their eyes, Schweikert said. 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.

Schweikert, Johnsen and Duke postdoctoral associate Bob Fitak focused on the hogfish, or Lachnolaimus maximus, which spends its time in shallow waters and coral reefs in the western Atlantic Ocean, from Nova Scotia to northern South America. It can make its skin whitish to blend in with the sandy bottom of the 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.

The researchers 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 cuttlefish and octopuses suggest the same molecular pathway that detects light in eyes may have been co-opted to sense light in the skin.

But Schweikert and colleagues 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 in their surroundings and bring about a color change remains unclear, 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, "the results suggest that fish have found a new way to 'see' with their and change color quickly," Schweikert said.

Explore further: Study demonstrates that octopus's skin possesses same cellular mechanism for detecting light as its eyes do

More information: Lorian E. Schweikert et al, De novo transcriptomics reveal distinct phototransduction signaling components in the retina and skin of a color-changing vertebrate, the hogfish (Lachnolaimus maximus), Journal of Comparative Physiology A (2018). DOI: 10.1007/s00359-018-1254-4

Related Stories

Genetic mutation in whale eyes may increase mortality risks

October 24, 2016

Scientists have found that a genetic mutation in the eyes of right whales that hampers their ability to see in bright light may make them more susceptible to fatal entanglements in fishing gear, one of the major causes of ...

Squid skin could be the solution to camouflage material

February 22, 2018

Cephalopods—which include octopuses, squid, and cuttlefish—are masters of disguise. They can camouflage to precisely match their surroundings in a matter of seconds, and no scientist has quite been able to replicate the ...

Recommended for you

Team discovers a new take on early evolution of photosynthesis

April 24, 2018

A team of scientists from Arizona State University's School of Molecular Sciences has begun re-thinking the evolutionary history of photochemical reaction centers (RCs). Their analysis was recently published online in Photosynthesis ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.