INCREASED DRAG, AND THUS LOWER SPEED - A COST FOR MORPHOLOGICAL DEFENSE IN BOSMINA (EUBOSMINA) (CRUSTACEA, CLADOCERA)

1. The swimming speed of two forms, an extreme and a typical, within t he cladoceran subgenus Eubosmina were examined using a three-dimension al video-technique. The extreme form has a very high carapax and extre mely long antennule, features probably involved in predator defence. 2 . It was found that the extreme form swam almost 40% slower than the t ypical form. 3. Calculations show that the extreme form had to work at least 12% harder to swim at the same speed, or if it used the same am ount of energy to swim, the extreme form would swim 6% slower. Increas ed drag, because of its distinguishing carapax and antennule, is thus the most likely explanation for the slower swimming speed of the extre me form, assuming it selects the same power output. 4. Swimming speed can be correlated to food intake either by the frequency of hits to ed ible food particles or by the time to swim from a poor food patch to a good one. So the reduced speed is probably a great cost for the extre me form.