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Light-Emitting Organ of Squid Also Senses Light

In addition to their prominent eyes that sense light, some squid have an organ that emits light. This light organ contains symbiotic luminous bacteria that produce light that is used by the squid to avoid predators. The light is believed to make the squid appear as bright as the ocean surface above them and thus obscure them from predators below. Now, researchers at the University of Wisconsin-Madison have obtained evidence that the light-emitting organ also senses light. "Until now, scientists thought that illuminating tissues in the light organ functioned exclusively for the control of the intensity and direction of light output from the organ, with no role in light perception," said lead author Dr. Margaret McFall-Ngai. "Now we show that the E. scolopes squid has additional light-detecting tissue that is an integral component of the light organ." Dr. McFall-Ngai added that "the tissues may perceive environmental light, providing the animal with a mechanism to compare this light with its own light emission." The findings may lead to future studies that provide insight into the mechanisms of controlling and perceiving light. The work was published in the June 2 issue of PNAS. [Press release]