Polarization signals in mantis shrimps

While color signals are well known as a form of animal communication, a number of animals communicate using signals based on patterns of polarized light reflected from specialized body parts or structures. Mantis shrimps, a group of marine crustaceans, have evolved a great diversity of such signals, several of which are based on photonic structures. These include resonant scattering devices, structures based on layered dichroic molecules, and structures that use birefringent layers to produce circular polarization. Such biological polarizers operate in different spectral regions ranging from the near-UV to medium wavelengths of visible light. In addition to the structures that are specialized for signal production, the eyes of many species of mantis shrimp are adapted to detect linearly polarized light in the ultraviolet and in the green, using specialized sets of photoreceptors with oriented, dichroic visual pigments. Finally, a few mantis shrimp species produce biophotonic retarders within their photoreceptors that permit the detection of circularly polarized light and are thus the only animals known to sense this form of polarization. Mantis shrimps use polarized light in species-specific signals related to mating and territorial defense, and their means of manipulating light's polarization can inspire designs for artificial polarizers and achromatic retarders.