A bio-inspired polarization camera has given marine biologists a better understanding of the mating rituals of the northern swordtail fish. The camera contains nanomaterials that allow it to capture the polarization properties of light in real time. Researchers used the camera to find that female swordtail fish are attracted to "polarization ornament" patterns visible in large male swordtail fish. The camera's developer, Dr. Viktor Gruev, an associate professor of computer science and engineering at Washington University in St. Louis, said, "There is a lot of social interaction among the fish. We saw the female fish checking out the large males and looking at their polarization ornaments. During the whole courting behavior, the more polarization a male has, the higher the chance for mating.” Using the new camera, researchers found that male swordtail fish possessing certain "polarization ornaments" were more appealing to females. The researchers changed the polarization to allow the large males with high contrast to amplify the effect of the polarization ornaments, he added. “When we suppressed the polarization ornaments externally with light, the females didn’t pay attention to the males,” Gruev said. “When we changed the light sources to change the polarization signals on the fish body, the social interactions between female and male swordfish significantly increased.” Previous research has found polarization sensitivity in invertebrate animals, including the octopus, but this recent study is the first demonstration of such behavior in vertebrate animals, the researchers said. The camera has also been used in other applications in marine biology and is now being used at the WUSTL School of Medicine to help physicians and researchers detect cancer cells in early stages of development. The work was funded by the U.S. Office of Naval Research, the U.S. Air Force Office of Scientific Research and the National Science Foundation. The research was published in Proceedings of the National Academy of Sciences (doi: 10.1073/pnas.1321368111). For more information, visit www.wustl.edu.