INDIVIDUAL SWIMMING BEHAVIOR OF DAPHNIA - EFFECTS OF FOOD, LIGHT AND CONTAINER SIZE IN 4 CLONES

Different species of Daphnia show differences in their swimming behavi or under different environmental conditions. We measured the three-dim ensional swimming behavior of individual adult female Daphnia in the m esocosm-scale Plon plankton towers (6400 l) and in small (183 mi) obse rvation chambers. Speed, sinking rate and turning angle were chosen as optimal variables for describing the free-swimming animals of four sp ecies. Speed, sinking rate and turning angle show uniformity of varian ce among treatments, and they are relatively independent. Light level and food level strongly affected swimming behavior. Light and food eff ects tended to be independent, although there were two instances of sy nergism (out of 12 possible interactions). Each of the four species (o ne clone per species) showed a unique response to food and light, whic h may reflect the diverse environmental origin of each clone. Swimming behavior was consistently different between the small-scale (183 mi) observation chamber and the mesocosm-scale (6400 l) plankton tower, su ggesting 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.