ADAPTIVE FEEDING-BEHAVIOR OF DAPHNIA-MAGNA IN RESPONSE TO SHORT-TERM STARVATION

Feeding behavior of Daphnia has been intensely studied, yet the genera lly observed behavior of maximal feeding at low food concentrations co ntradicts the predictions of optimal foraging theory. To explore this inconsistency, I investigated the behavioral feeding response of Daphn ia magna through direct observation of thoracic filtering appendage be at rates at low food concentrations. I observed animals that were subj ected to either varying starvation periods or to different food concen trations prior to the experiments. Starvation led to a behaviorally me diated decrease in appendage beat rate, which depended on the food con centration at which the daphnids were cultured. Starved daphnids consi stently showed an almost immediate increase in their appendage beat ra te once food was added, irrespective of the length of the starvation p eriod (from 1 to 3 d). Therefore, the initial decrease in appendage be at rate displayed by animals during starvation could not have been cau sed by the deprivation of energy (exhaustion) alone. Furthermore, the food conditions under which the animals were cultured influenced the b ehavioral response. After 1 h of starvation, animals cultured at high food level showed no behavioral response to the addition of food, whil e animals cultured at low food level increased their appendage beat ra te significantly. The results of this study contradict the maximal fee ding strategy and highlight problems of the optimal foraging strategy.