'Bioinspiration': A UNCW scientist's work on the humble hogfish could have far-reaching implications
UNCW’s Dr. Lori Schweikert recently published a study, co-authored with PhD student, Lydia Naughton, in the scientific journal, Nature Communications, on how special light receptors embedded within hogfish skin allow them to ‘see’ themselves. The spark for the research started when she saw a hogfish rapidly change colors in her boat.
Back in 2016, Schweikert was fishing down in the Florida Keys when she captured one of these hogfish, and when she picked the fish up, the side that had been facing the deck had turned white, which matched the color of the boat’s surface.
“It was like, ‘Maybe the skin can actually see its surrounding environment?’ In hindsight, it was likely pressure or temperature of the deck that caused that to happen, but when I looked into the body of literature to see if there was any merit to that, scientists have found that virtually all animals that do dynamic color change have a light detecting capacity of the skin, but nobody knows why,” Schweikert said.
But Schweikert’s study was one piece of the ‘why’ puzzle.
“We were the first to show that these light-sensitive proteins are buried beneath their screen of color change. It's as if they're viewing their own color change. [...] The way that I tried to explain it to people is, if you had to get dressed in the morning, and you had no mirror, how would you know that you dressed appropriately?” she said.
The color change that the hogfish undergo is mainly for camouflage to tell a predator to go away, or a way to signal information to another hogfish.
These proteins essentially tell the fish, “‘I'm the color I'm supposed to be’ or ‘I'm not really the color I should be, and I should fix it,” she said.
This new cell, the one that Schweikert’s team discovered, has a structure that is specialized enough to hold all this protein for photoreception.
“So this might be one of the first examples of a specialized photoreceptor outside of the central nervous system of a vertebrate animal,” Schweikert said.
She added that this light-sensitive protein contains ‘opsin’, which “is the same protein that allows you to detect light with the retina. So in the hogfish, the opsin that allows you to sense blue light in your retina is the same opsin that was present in the fish’s skin. It's a blue light detector.”
And this new cell discovery is a photoreceptor that contains this opsin. They work in concert with these specialized cells called chromatophores.
“These are the colorful cells that contain pigment. And when the hogfish wants to darken, for example, [the chromatophores] disperse all that pigment to the edge of the cell. And when it wants to look light, or white, for example, it aggregates the pigment to the cell center, allowing light to pass by and reflect back. And so when these individual cells activate, it causes color change over the body,” she said.
While Schweikert’s lab specializes in visual ecology, her work has implications for technology in terms of “bioinspiration.”
“So one big concept in tech is smart systems and autonomous robots, things like self-driving cars, all of these systems are dependent on knowing how they're behaving in a changing environment. So for hogfish, they need to be aware of how they're behaving, and their color changes in their changing environment, so we can look at the architecture of the system; we can look at neural computations in the system, and try to draw principles that might help scientists to create this kind of technology,” Schweikert said.
After the success of this study, Schweikert said there’s still a lot more to find out about what exactly the hogfish’s cells are doing.
“Is it really a photoreceptor? Is it a neuron? What is the fundamental neurobiology of understanding skin? Is it photoreception? The other direction is, okay, well, now we understand the building blocks of how a complex behavior like color change can occur, so how are these animals actually doing it? How are they generating these complex patterns that they're making all these chromatophores work in concert to generate something important? And that kind of large-scale understanding is the next step of this work,” she said.
But at the end of the day, what Schweikert finds most fascinating about color-changing marine species is that they can tell us about what animals need to survive in their world – and that involves a complex feedback system.
“It's actually the rule and not the exception in biology, nearly all of our physiological systems, like blood sugar, blood pressure, all of our behaviors, like speech production, or running up uneven stairs are all based on this monitoring of our own performance feedback,” she said.