Molly Cummings studies the evolutionary forces that shape the ways that animals communicate. She studies how fish and frogs camouflage themselves from predators, how they evolve signals to attract potential mates, and how the visual system and brain processes these different signals. Her recent research has explored how fish use polarized light to both hide and communicate, as well as identified what brain regions and genomic pathways are involved in mate choice decision-making.
6/21/10 — University of Texas research dive in the Gulf of Mexico off Port Aransas, Texas Monday June 21, 2010. — Photo by Erich Schlegel
Fish Skin Provides Invisibility in Open Ocean
Molly Cummings examines fish in the open ocean to better understand how they use polarized light for camouflage. Credit: Erich Schlegel.
Many animals camouflage themselves to avoid being eaten by predators. It can be as simple as a chameleon changing the color of its body to match its environment. Fish swimming in the open ocean, however, have an especially hard time blending in because the light properties of water change throughout the day.
Researchers have found that fish that live in the open ocean, such as these lookdowns, reflect polarized light from their skin in a way that makes them seemingly disappear from predators’ view. Credit: Erich Schlegel.
The part of light that changes the most throughout the day is called polarization, and my colleagues and I have discovered that some fish use this feature to hide in plain sight. Under the surface of the water, light tends to be polarized. In other words, the light waves all travel in the same plane; and the direction of this polarization will change with different positions of the sun. Predators have evolved a means to detect polarized light, so we wondered whether fish also evolved a means to hide in polarized light.
Molly Cummings using the underwater apparatus to conduct the experiment. Credit: University of Texas at Austin.
We used the open ocean off the coasts of Florida and Curaçao as a natural laboratory. We put live fish in a restraint and compared the polarization of light reflecting off these fish to the polarization of background light. And we studied the fish from over a thousand different viewing angles and at different times of day.
And what we found is that these open ocean fish species manipulate the polarization of light reflecting from their skin in a way that would make it much harder for predators to see them in open water. But fish from coastal environments, where the polarized light field is far less complex, did not.
It’s wonderful to discover that animals can do something so complex and clever using a feature of light we can’t even see. This newly discovered trick might also someday help the U.S. Navy hide vessels in the open ocean.
Simulated view of how the lookdown fish would appear in polarized light with mirrored skin (left) versus skin that reflects polarized light (right). Images are from simulations created by the Cummings lab, University of Texas at Austin.
Video: How Fish Minimize Their Visibility to Predators in Open Waters (AAAS)