SIZE-SPECIFIC SWIMMING BEHAVIOR OF DAPHNIA-PULEX

Body length affects several aspects of the behavior of quietly swimming Daphnia pulex. Swimming and sinking rates were measured at 0.033 s intervals during the 'hops' characteristic of Daphnia swimming behavior. Larger animals swim faster, cover more distance, and produce more powerful swimming strokes. Larger Daphnia also sink faster, but the sinking rate scales as length to the 0.58 power, far lower than the power of 2.00 predicted by Stokes Law considerations. The number of hops s-1 was independent of body size, although a theoretical analysis predicts hopping rate (antennal beat frequency) should increase as body length squared. Turning behavior, measured as the ratio of displacement to total distance, during 5 s, is also independent of body size. Independence of several parameters of body motion and body size implies that factors other than simple mechanics affect Daphnia swimming behavior.