CS39A Zooplankton - Feeding, Reproduction, Growth and Molecular Diversity
Date: Tuesday, June 11, 2002
Time: 2:45:00 PM
Location: View Royal
 
StraileD, University of Konstanz, Konstanz, Germany, Dietmar.Straile@uni-konstanz.de
Jankowski, T, , University of Konstanz, Konstanz, Germany, Thomas.Jankowski@uni-konstanz.de
 
INDUCTION OF DAPHNIA SEXUAL REPRODUCTION IN MESOCOSM EXPERIMENTS: DENSITY DEPENDENCE AND CLONAL VARIABILITY
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Three years of field studies have shown that sexual reproduction of two Daphnia species in Lake Constance is restricted to two time periods, with D. galeata reproducing sexually in late spring and D. hyalina in autumn. In order to test the role of photo period, food limitation and crowding for the lack of sexual reproduction in summer, we induced sexual reproduction in mesocosms in July by fertilizing mesocosms, i.e., inducing an algae bloom and sub-sequent Daphnia population growth and overexploitation of algae. Daphnids produced males and ephippia in fertilized mesocosms, whereas they did not so in unfertilized controls. Using allozymes, species specific and clonal differences in the relative investment into sexual versus parthenogenetic reproduction were analyzed. Our results suggest that the lack of crowding conditions during summer inhibits Daphnia sexual reproduction thereby reducing the frequency of hybridization.