Researchers at UCSB have found a protein in a species of iridescent cephalopods that allows them to dynamically change their color and reflectivity, providing them with a way to attract mates and camouflage even in shallow waters.

The squid species in question, Loligo, is different from other squids due to its ability to change its iridescence at will.

Alison Sweeney, co-author of the study and a post-doctoral researcher at UCSB’s Dept. of Molecular, Cellular and Developmental Biology, said the squids may have developed dynamic iridescence as an adaptation to light distribution in shallow water.

“Lots of things have structural color, [these can be] useful qualities for many different functions such as signaling to mates, camouflage or conspicuousness, depending on the match of the iridescence to the environment of the animal,” Sweeney said. “We think that the squid has evolved dynamic iridescence since it lives in relatively shallow waters and shallow water is a particularly dynamic light environment, due to wave lensing and other phenomena leading to bright beams of light passing through the water column.”

The proteins, dubbed reflectins, have been found by the researchers to react with acetylcholine, a common neurotransmitter found in nature. According to Sweeney, when the acetylcholine was introduced to the tissue, the reflectins reacted and changed the tissue’s refractive index.

“[The study] uses acetylcholine. Different receptors on different types of cells have different responses when acetylcholine binds to them,” Sweeney said. “Acetylcholine binding triggers a cell-signaling cascade which ultimately results in reflectin proteins getting decorated with phosphates … by shifting and reorganizing the charges on the reflectin protein … [the protein has] different assembly dynamics. … The more it compresses, the higher the refractive index, which results in shorter wavelengths being reflected off. … As the cascade continues, blue/violet wavelengths are refracted.”

In the future, Sweeney said she hopes to observe the squid in a more natural environment to better understand how it utilizes its cloaking mechanism.

“We don’t really understand the details of the match between the squid’s dynamic iridescence capabilities and the complicated light environment of the shallow ocean. This is partly because it is pretty difficult to do rigorous observations of squid in their natural environment,” Sweeney said. “We are going to start experiments manipulating the light environment of the squid in the lab, as well as blindfolding squid, to see how this changes their response, to try to better understand how they respond to the dynamic environment where they live.”

Sweeney said the peculiar attributes of the Loligo have raised important questions about semisolids and their importance in physics.

“Basically, we do not know much about gels or semisolid materials in physics and materials science,” Sweeney said. “The squids are making us pay attention to things we otherwise wouldn’t.”