Profile of a mantis shrimp.
Scientists are getting closer to understanding the impressive array of 16 photoreceptors within the eye of the mantis shrimp. But the structural details of the UV receptors have been fuzzy until now. A team of researchers from the University of Maryland, U.S.A., discovered that the mantis shrimp’s six different UV receptors are based on pigments called mycosporine-like amino acids (MAAs), a pigment other animals use as a natural sunscreen (Curr. Biol., DOI: http://dx.doi.org/10.1016/j.cub.2014.05.071)
The team employed several techniques to classify the UV receptor pigments, including biochemical analysis, spectral tuning modeling and fluorescent microscopy. They found that the mantis shrimp’s UV receptors contain one of two visual pigments paired with one of four short- or long-pass UV-specific optical filters made from MAAs. The optical filters block different wavelengths of light, making them sensitive to a narrow range of wavelengths. UV receptor specificity along with other complex photoreceptive abilities may allow the mantis shrimp to identify and respond to light cues completely within the visual system. By bypassing the brain, their response time is faster—an obvious benefit for a predator.
The team was surprised to learn that one of the two visual pigments was found paired with each of the four different filters. They referred to this discovery as “the most complex example known of filtering to multiply spectral sensitivities.” In comparable color vision structures of reptiles and birds, cone color droplets are paired with their own visual pigment to sharpen rather than diversify spectral sensitivity.
Lead author Michael Bok notes that the team is not sure why the mantis shrimp needs such complex visual abilities, but speculates that UV vision may provide a way for mantis shrimp to secretly communicate with each other in a visual language that other animals can’t see.