Influence of Egg Sacs on the Swimming Performance of Freshwater Cyclopoid Copepods

Female cyclopoid copepods carry their embryos in egg sacs that impact swimming performance until nauplii hatch. We studied kinematic parameters and mechanical energy of small routine jumps and large escape jumps of non-egg-carrying (NEC) and egg-carrying (EC) females of Mesocyclops leuckarti and Macrocyclops albidus. The drag and body acceleration costs for EC females of M. leuckarti and M. albidus during routine jumps were 28 and 40%, respectively, higher than those for NEC females moving at the same speed. Maintaining position in the water column by small jumps was more costly for EC females, requiring 2.2-2.3 times more jumps and energy. Consequently, the persistence of EC females was limited in the open water. In M. leuckarti and M. albidus, the average speed and distances of jumps were 5-6 and 1.5-2.2 times higher, respectively, and the duration of jumps was 2.2-2.5 times shorter during escape than routine swimming. The maximum jumping speeds of NEC females, 40.6 and 50.5 cm s-1, respectively, were 12-14% higher than those of EC females, whereas their power and cost of transport were 16 and 23% lower, respectively. These results clearly indicated that egg sacs impair swimming and increase energetic costs of movement.