Individual swimming behavior of Daphnia: Effects of food, light and container size in four clones

Abstract

Different species of Daphnia show differences in their swimming behavior under different environmental conditions. We measured the three-dimensional swimming behavior of individual adult female Daphnia in the mesocosm-scale Plon plankton towers (6400 1) and in small (183 ml) observation chambers. Speed, sinking rate and turning angle were chosen as optimal variables for describing the free-swimming animals of four species. Speed, sinking rate and turning angle show uniformity of variance among treatments, and they are relatively independent. Light level and food level strongly affected swimming behavior. Light and food effects tended to be independent, although there were two instances of synergism (out of 12 possible interactions). Each of the four species (one clone per species) showed a unique response to food and light, which may reflect the diverse environmental origin of each clone. Swimming behavior was consistently different between the small-scale (183 ml) observation chamber and the mesocosm-scale (6400 l) plankton tower, suggesting that container size affects swimming behavior: in the smaller chamber, Daphnia, regardless of species, swam slower, sank slower and tended to move in straighter paths.