POLAROTAXIS IN COPEPODS. I. AN ENDOGENOUS RHYTHM IN POLAROTAXIS IN CYCLOPS VERNALIS AND ITS RELATION TO VERTICAL MIGRATION

¹ Bingham Laboratory, Yale University, New Haven, Conn. 06520

1. A series of laboratory experiments on the fresh-water copepod, Cyclops vernalis, revealed an endogenous rhythm in its orientation to polarized light. The copepod swam perpendicular to the plane of polarization at the beginning and end of a 12-hour diurnal light period, but swam parallel to the plane of polarization midway through this light period.

2. The rhythm was not present under all experimental conditions, being released only when the intensity of light from above was equal to that from the side. Under other experimental conditions, the copepods swam perpendicular to the plane of polarization at all times during the light period.

3. A pattern of horizontal polarization, crudely simulating the simplest natural underwater pattern, was found to provide Cyclops vernalis with vertical-horizontal reference coordinates for spatial orientation.

4. Changing intensities of polarized light induced net displacements of the population, thus effecting vertical migration in the laboratory.

5. The ratio of overhead to lateral light intensity provided a visual cue indicating water depth. The diurnal rhythm in polarotaxis operated only with deep-water intensity ratios of horizontal and vertical light and served to orient deep-water individuals in a horizontal plane at midday, thus inhibiting vertical swimming patterns (which occur at dawn and dusk) that might carry them to the surface at that time.

This article has been cited by other articles:

				I Novales Flamarique, H. Browman, M Belanger, and K Boxaspen Ontogenetic changes in visual sensitivity of the parasitic salmon louse Lepeophtheirus salmonis J. Exp. Biol., January 6, 2000; 203(11): 1649 - 1657. [Abstract] [PDF]