BEHAVIOR OF DAPHNIA IN POLARIZED LIGHT

Abstract

1. Daphnids illuminated by a single vertical beam of polarized light swam approximately perpendicular to the polarization plane. 2. Daphnids illuminated by a single pair of opposed horizontal beams of light oriented toward the brighter light of the pair. 3. Daphnids illuminated by two pairs of opposed horizontal beams set at right angles to each other swam in the beam of the brighter pair of light beams. 4. Daphnids illuminated simultaneously by three beams (one polarized and coming from overhead, the other two nonpolarized and horizontally opposed, parallel to the polarization plane of the overhead light) responded to the overhead polarized light when its intensity was greater than 20 times that of the horizontal beams. When the intensity of the overhead beam of polarized light was less than 20 times that of the horizontal beams, the daphnids responded to the horizontal opposed beams instead of the polarized beam from overhead. 5. The changes in behavior induced by various intensity combinations of overhead and horizontal light beams were in good agreement with the changes predicted from daphnid eye structure. 6. Daphnids exhibiting drug-induced negative phototaxis were shown to possess simultaneously a secondary weak positive phototaxis always executed at right angles to the negative phototaxis. This weak positive phototaxis at right angles to the negative phototaxis is proposed to account for photonegative daphnids which orient perpendicular to the polarization plane of a vertical beam of light.