Fine structure and optical properties of biological polarizers in crustaceans and cephalopods

Abstract

The lighting of the underwater environment is constantly changing due to attenuation by water, scattering by suspended particles, as well as the refraction and reflection caused by the surface waves. These factors pose a great challenge for marine animals which communicate through visual signals, especially those based on color. To escape this problem, certain cephalopod mollusks and stomatopod crustaceans utilize the polarization properties of light. While the mechanisms behind the polarization vision of these two animal groups are similar, several distinctive types of polarizers (i.e. the structure producing the signal) have been found in these animals. To gain a better knowledge of how these polarizers function, we studied the relationships between fine structures and optical properties of four types of polarizers found in cephalopods and stomatopods. Although all the polarizers share a somewhat similar spectral range, around 450-550 nm, the reflectance properties of the signals and the mechanisms used to produce them have dramatic differences. In cephalopods, stack-plates polarizers produce the polarization patterns found on the arms and around their eyes. In stomatopods, we have found one type of beam-splitting polarizer based on photonic structures and two absorptive polarizer types based on dichroic molecules. These stomatopod polarizers may be found on various appendages, and on the cuticle covering dorsal or lateral sides of the animal. Since the efficiencies of all these polarizer types are somewhat sensitive to the change of illumination and viewing angle, how these animals compensate with different behaviors or fine structural features of the polarizer also varies.

Polarisation signals: a new currency for communication

“…In the marine world of these highly successful invertebrate groups is the arms race or selection for polarisation secrecy still underway? Stomatopods possess circular polarisation vision and circular polarising signals, and these are not visible to cephalopods as far as we know (Figs 2D, 6 and 7G;Chiou et al, 2005Chiou et al, , 2007Chiou et al, , 2008a. Does this indicate a step ahead in the communication arms race?…”

“…The result is a strong horizontal signal against a non-polarising background, ( Fig. 4; Chiou et al, 2005Chiou et al, , 2008aHow et al, 2014b;Cronin, 2018). Marshall (2010, 2011) showed that cuttlefish and squid orient the microvilli in adjacent photoreceptors mainly H and V relative to the outside world (Fig.…”

“…One of the least attended to but most necessary set of observations in any potential signalling scenario comes from observing the animal in situ and thinking through its biology and behavioural repertoire. The alternating behaviours of revealing and covering up polarised arm stripes on cuttlefish or the polarised wings and carapace in butterflies and stomatopods, respectively, are good examples of this sort of desirable data (Sweeney et al, 2003;Chiou et al, 2008a;Mathger et al, 2009a,b). Quantification of the polarised light environment and, in particular, polarised background is particularly worthy of attention, and it is relatively straightforward with the now frequently used portable spectrophotometers and appropriate filters.…”

Thresholds of polarization vision in octopuses

“…Polarization vision is widespread in nature ( Roberts et al, 2011 ), mainly among the invertebrates, where it contributes to a variety of behavioural tasks including navigation ( Wehner, 1976 ), habitat localization ( Schwind, 1991 ) and communication ( Chiou et al, 2008 ). In terrestrial environments, this sensory capacity is best understood in the dorsal rim area of the eye, which is directed towards the sky to enable the detection of the pattern of celestial polarization ( Wehner, 1976 ).…”

A Biomimetic Model of Adaptive Contrast Vision Enhancement from Mantis Shrimp

“…There is also crayfish visual motion detection [ 9 ], the predation of transparent zooplankton by marine life [ 10 ], and fiddler crab detection of objects in mudflats and other environments [ 11 ]. Among those polarization-sensitive creatures, cephalopods and crustaceans are in the majority [ 12 ]. Their representatives are octopuses and mantis shrimp, respectively, and there are corresponding bionic studies of these creatures, such as the polarized vision chip made by simulating the octopus retina [ 13 ] and the biomedical polarization imaging sensor inspired by the compound eyes of the mantis shrimp [ 14 ].…”