Reproductive costs of Chaoborus-induced polymorphism in Daphnia pulex

Although the Chaoborus-induced spined morph of Daphnia pulex survives attacks by Chaoborus over twice as frequently as the typical morph, the spined morph is never found in the absence of Chaoborus. This implies that a disadvantage is associated with the spined morph in the absence of Chaoborus predation. The present study tested the hypothesis that the typical morph has a higher intrinsic rate of increase than the spined morph, by measuring several life history characteristics in controlled laboratory experiments at constant temperature and unlimited food.The results suggest that the spined morph of D. pulex takes longer to reach maturity, is smaller at maturity, but has similar egg number and egg size as the typical morph. These results are consistent with the hypothesis that the Chaoborus-induced spined morph is reproductively inferior to the typical morph.