The role of extraocular photoreceptors in newt magnetic compass orientation: Parallels between light-dependent magnetoreception and polarized light detection in vertebrates
Jb. Phillips et al., The role of extraocular photoreceptors in newt magnetic compass orientation: Parallels between light-dependent magnetoreception and polarized light detection in vertebrates, J EXP BIOL, 204(14), 2001, pp. 2543-2552
Theoretical models implicating specialized photoreceptors in the detection
of the geomagnetic field have been the impetus for studying the effects of
light on magnetic compass orientation. Magnetic orientation in flies, amphi
bians and birds has been found to be influenced by light, and in all these
groups a shift of approximately 90 degrees in the direction of magnetic com
pass orientation has been observed under certain wavelengths and/or intensi
ties of light. In the eastern red-spotted newt Notophthalmus viridescens, w
avelength-dependent effects of light on magnetic compass orientation appear
to result from an antagonistic interaction between short-wavelength (less
than or equal to 450 nm) and long-wavelength (greater than or equal to 500
nm) photoreception mechanisms. We have demonstrated that at least the short
-wavelength input to the newt's magnetic compass is mediated by extraocular
photoreceptors located in or near the pineal organ, and here we present ne
w findings that indicate that the putative longwavelength mechanism is also
associated with pineal photoreceptors. Interestingly, the amphibian pineal
organ mediates orientation to both the e-vector of plane-polarized light a
nd the magnetic field. Although the wavelength-dependence of the polarized
light orientation in amphibians has not been studied, polarization sensitiv
ity in fishes appears to be mediated by two antagonistic photoreception mec
hanisms that have similar spectral characteristics to those of the newts' m
agnetic compass response. These parallels, along with similarities in the t
ypes of receptors that are expected to be involved in light-dependent magne
toreception and polarized light detection, suggest that similar photorecept
ion mechanisms may mediate the light-dependent magnetic and polarized light
compasses.