Sep 22 2014
We have all seen a peacock show its extravagant, colorful tail feathers in courtship of a peahen. Now, a group of researchers have used a special camera developed by an engineer at Washington University in St. Louis to discover that female northern swordtail fish choose their mates based on a similar display.
A video polarimetry image of a large male northern swordtail in false color shows the differences in polarization on its surface.
Marine biologists at the University of Texas at Austin used a bioinspired polarization camera developed by Viktor Gruev, PhD, associate professor of computer science & engineering in the School of Engineering & Applied Science to make the discovery. His camera has been used in other applications in marine biology and also is now being used at Washington University School of Medicine in St. Louis to help physicians and researchers see cancer cells very early in development.
In the new study, the researchers found that female swordtail fish are attracted to certain patterns, called polarization ornaments, visible in polarized light in large male swordtail fish.
“There is a lot of social interaction among the fish,” Gruev said. “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.”
Various animals can detect polarization, or the alignment of light waves in a plane. Previous research found polarization sensitivity in invertebrate animals, including octopus, but this is the first research to find polarization behavior in vertebrate animals.
The research was published online Sept. 2, 2014, in the Proceedings of the National Academy of Sciences Early Edition.
Gruev’s camera is similar to polarized sunglasses, which reduce glare by blocking polarized light. The camera is built with nanomaterials inside the camera, allowing it to capture the polarization properties of light in real time.
“We changed the polarization so that the large males with high contrast showed good contrast in their polarization ornaments,” Gruev said. “When we suppressed the polarization ornaments externally with light, the females didn’t pay attention to the males. When we changed the light sources to change the polarization signals on the fish body, the social interactions between female and male swordfish significantly increase.”
Gruev is an expert in polarization and signal processing. The camera is a replication of the visual system of the mantis shrimp, which is among the most sophisticated vision of all animals.
Gruev and several other researchers from Washington University also recently published a review paper in the Journal of the Proceedings of the IEEE on bioinspired polarization imaging sensors and their applications in biomedicine.
The Washington University researchers are Samuel Achilefu, PhD, professor of radiology and of biochemistry & molecular biophysics at the School of Medicine and of biomedical engineering at the School of Engineering & Applied Science; Tauseef Charanya, a predoctoral trainee in radiology at the School of Medicine; Lindsey Kahan, an undergraduate student in mechanical engineering & materials science; Spencer P. Lake, PhD, assistant professor of mechanical engineering; Samuel B. Powell, a graduate research assistant in computer science & engineering; Barani Raman, PhD, assistant professor of biomedical engineering; and Debajit Saha, a postdoctoral research associate in biomedical engineering.
This research was funded by the Office of Naval Research, Air Force Office of Scientific Research and the National Science Foundation.