Polarization signaling in stomatop crustaceans and cephalopod mollusks

Polarization vision has been studied in a great variety of animals like insects, fishes, cephalopods, and mantis shrimps. Most studies imply that the main purpose of polarization vision is to detect the polarized light from the environment. However, the recent discovery of body parts reflecting polarized light patterns in some species of mantis shrimps and cephalopods suggests the existence of an intraspecific polarization signaling system in these animals. Most of these animals live in shallow water environment where the variations of the ambient spectrum of light are the greatest. Visual signals based not on the spectrum but on the polarization property of light can provide great benefit in such environment. To test this hypothesis, I characterized the properties of the polarized light reflections and investigated the mechanisms that cause these polarization signals. Using imaging polarimetry and spectropolarimetry, four types of polarizers were found. Each type of polarizer has distinctive properties and is based on a different mechanism. On the other hand, all these polarization signals share a similar spectral range which is close to the wavelengths best transmitted by seawater. Interestingly, one type of polarization signal is circularly polarized which is not commonly found in the natural environment. Using intracellular physiological recordings, it was demonstrated that eyes of one stomatopod crustacean species, Odontodactylus scyllaus, can perceive circularly polarized light. Furthermore, circularly polarized light of opposite handedness entering their eyes is converted into linearly polarized light by a form birefringence retarder and perceived by receptors underneath the retarder. Behavioral studies using Haptosquilla trispinosa demonstrated that polarized visual signals are used during courtship display. Polarization signals may indicates the fitness of an approaching potential mate. To sum up, this work studied the biological polarization signaling systems of some marine invertebrates in three aspects: signals, receivers, and functions. The results indicate that these polarized-light signals are well adapted and useful in the underwater environment these animals inhabit