The night vision of frogs and toads appears to be superior to that of all other animals. These amphibians have the ability to see color even when it is so dark that humans are not able to see anything at all. This has been shown in a new study by researchers from Lund University in Sweden, together with colleagues. Most vertebrates, including humans, have two types of visual cells located in the retina, namely cones and rods. The cones enable us to see color, but they usually require a significant amount of light and therefore stop working when it gets dark, in which case, the rods take over so that we can at least find our way home, albeit in black and white. In toads and frogs, the rods are a bit special, however. It was previously known that toads and frogs are unique in having rods with two different sensitivities. This has not been found in other vertebrates, and it is also the reason why researchers have long suspected that frogs and toads might be able to see color also in low-light conditions. The new study is the first to prove this to be true, and the results exceeded all expectations. "It's amazing that these animals can actually see color in extreme darkness, down to the absolute threshold of the visual system. These results were unexpected,” says Professor of Sensory Biology Almut Kelber at the Faculty of Science, Lund University. It was during the third of three experiments that the researchers discovered that frogs are able to use their rods to distinguish color in extreme darkness. The researchers studied the frogs in a situation that is as serious as it is common, namely, when frogs need to find their way out in case they are trapped in conditions of complete darkness. This is potentially an everyday occurrence, taking place in dark dens and passageways on the ground.
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