Genetic control of predator avoidance behaviour in Daphnia

1. The vertical migration behaviour in electrophoretically distinguishable clones of Daphnia magna Straus was investigated. 2. Clones differed significantly in their tendency to stay near the surface of the tank during the light phase of the daily light/dark cycle, indicating that vertical migration has a genetic component. 3. There was a significant difference in behaviour between juvenile and adult Daphnia: overall the juveniles stayed closer to the water surface than the adults, but the characteristic pattern of clonal differences persisted in the juveniles. 4. When an adult population of each clone was exposed to a fish predator in an experimental tank, the position a clone maintained in the tank at the start of the day had a direct effect on its survival. Clones remaining near to the surface of the water suffered greatest predarion.