COST OF SWIMMING BY DAPHNIA DURING DIEL VERTICAL MIGRATION

Daphnia hyalina was grown under simulated conditions of diurnal vertical migration in vertical flow chambers, and its life-history parameters were evaluated. The amplitudes of the migrations were 3 and 60 m d-1; food conditions were 0.1 and 1.0 mg C liter-1. None of the investigated parameters (fecundity, individual growth rate, age of maturation) was significantly different between long- and short-distance migrating populations at high levels of food, whereas at low levels of food only the individual growth rate was higher in the short-distance migrating Daphnia. These results suggest that the energy spent to travel the vertical distance does not account for the metabolic costs of diurnal vertical migration.