Polarization Sensitivity in Amphibians: An Update

Polarization sensitivity (PS) in amphibians has been examined in some species of anurans and urodelans. Gymnophiones, on account of their tiny eyes and fossorial or aquatic lifestyles are considered unlikely candidates for PS. Some anura and urodela have been shown to detect the direction of polarization with photoreceptors of the pineal organ rather than their lateral eyes. An ordered array of light-absorbing visual molecules is paramount for PS, but an ordered array of radical pairs generated through photo-induced electron transfer is also essential for magnetoreception, which suggests that there is some interaction between the two senses. An anatomical requirement for PS is a constant and characteristic orientation of the photoreceptor’s disc membranes. A closer look at ultrastructural modifications in different retinal regions of species that are expected to be polarization sensitive, seems warranted. Polarization sensitivity may help to relocate breeding sites in philotropic species and to improve visibility of prey in predatory larval and adult urodeles plus those few anurans that hunt underwater. Furthermore, it could possibly be of assistance in separating overlapping shadows and play a role during courtship in species with distinct sexually dimorphic colouration.