With 'biological sunscreen,' mantis shrimp see the reef in a whole different light

In an unexpected discovery, researchers from the University of Maryland Baltimore County and the University of Maryland Center for Environmental Science have found that the complex eyes of mantis shrimp are equipped with optics that generate ultraviolet (UV) color vision. Mantis shrimp's six UV photoreceptors pick up on different colors within the UV spectrum based on filters made from an ingredient other animals depend on as built-in biological sunscreen, according to research reported in the Cell Press journal Current Biology on July 3.

"The mantis shrimp visual system contains six types of photoreceptors functioning completely outside the visual range of humans," says Michael Bok of the University of Maryland Baltimore County.

"Surprisingly, they produce their six UV photoreceptors using only two types of visual pigments by pairing one visual pigment with one of four UV filters. The UV filters block certain wavelengths of light from reaching the photoreceptors, chromatically shifting their sensitivity."

The filters are composed of so-called mycosporine-like amino acids (or MAAs), which are commonly found in the skin or exoskeleton of marine organisms, where they absorb damaging UV rays. They do the same thing in mantis shrimp eyes, but for an entirely novel purpose.

"The effect is akin to putting red-tinted glasses over your eyes that block other wavelengths of light, except this is being done at the photoreceptor cellular level in shrimp," Bok explains.

Dr. Allen Place of Institute of Marine and Environmental Technology helped identify the amino acids that filter and absorb the wavelenghts of light in the shrimp eyes. He likens the process to wearing "tunable sunglasses."

Exactly why mantis shrimp need such a sophisticated visual system remains mysterious, Bok says. Mantis shrimp use their eyes to navigate and spot predators and prey on the vibrant reef that is their home. Mantis shrimp also have complex social interactions that are likely mediated by distinct visual signals on their bodies.

Their complex eyes, which include 16 or more types of photoreceptors in all, may provide them with a complex color and polarization visual system without a big brain to post-process lots of information. In other words, their eyes may sense and respond to complex visual inputs without the need to think very hard about it, Bok explains.

Despite the new discovery, the researchers say, it's still tough to imagine the reef as mantis shrimp see it. "The way their eyes are built and how visual information is processed in their brains is so fundamentally different [from] humans that is very difficult to conceptualize what the world actually looks like to them," Bok says.

“The Institute of Marine and Environmental Technology prides itself on effective collaborations and Allen Place, one of our most collaborative faculty members, exemplifies this in his contributions to this fascinating research,” said Russell Hill, director of the Institute of Marine and Environmental Technology.

Located in Baltimore’s Inner Harbor, the Institute of Marine and Environmental Technology is a strategic alliance involving scientists at the University of Maryland Center for Environmental Science, the University of Maryland Baltimore and the University of Maryland Baltimore County. Scientists are engaged in cutting-edge research in microbiology, molecular genetic analysis and biotechnology, using marine life to develop new drug therapies, alternative energy and other innovations to improve public health and economic opportunities. IMET also contributes to sustainable marine aquaculture and fisheries in the Chesapeake Bay and marine ecosystems.

Courtesy of Cell Press. Photos by Michael Bok.