Wavelength specific effects of light on magnetic compass orientation of the eastern red-spotted newtNotophthalmus viridescens

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Abstract
The shoreward magnetic compass orientation of male eastern red-spotted newts (Notophthalmus viridescens) was examined in a visually-symmetrical indoor arena. Groups of newts were first trained in a water-filled outdoor tank with an artificial shore at one end and then exposed to a rapid elevation of the training tank water temperature just prior to testing. The directional response of individual newts was observed in the indoor arena in one of four horizontal alignments of the magnetic field (magnetic north at north, east, south or west). Magnetic bearings were pooled from the four magnetic field alignments for analysis. In each test, newts were alternately tested under either 450 nm or 550 nm light (of equal quantal flux) and under full spectrum light. Newts tested under full spectrum light exhibited shoreward magnetic orientation. The distribution of magnetic bearings exhibited by newts under 450 nm light was indistinguishable from that of full spectrum controls. In contrast, the distribution of bearings obtained under 550 nm light differed significantly from controls, exhibiting a shift in orientation of approximately 90° counterclockwise. This wavelength-dependent effect of light on magnetic compass orientation in newts is consistent with the proposed involvement of the visual system in magnetoreception.