A theoretical explanation of intensity-independent variation of polarisation sensitivity in Crustacean retinula cells

Abstract

1. Theoretical analyses of polarisation sensitivity (PS) in crustacean-type banded rhabdoms indicate that if depths of the orthogonally orientated layers of microvilli are equal, PS should be equal to the dichroic ratio of the rhabdom material (Shaw 1969; Snyder 1973). Published measurements of PS obtained by intracellular recording in various species show a wide range of values from 1 to 14 or more, the mode usually being about 10. 2. If variations in observed relative depth of the rhabdom layers are taken into account, together with the partially disordered transitional rhabdoms that are found during the early stages of rhabdom synthesis, the predicted range of PS values is similar to that actually measured if the dichroic ratio approaches 10. 3. It is predicted that PS will be wavelength dependent in those cells whose PS is markedly different from the dichroic ratio. PS at less effective wavelengths will be nearer the dichroic ratio than PS at peak wavelength. 4. Less variation in PS is expected, especially in the upper range, in species with short rhabdoms such as crayfish than in species with long rhabdoms such as large crabs.