Life history and body size evolution in Holopedium gibberum Zaddach (Crustacea, Cladocera)

SUMMARY. 1. Body size, development, sheath size and relative egg size were examined in two populations of Holopedium gibberum Zaddach. The populations were chosen because of differences in juvenile versus adult mortality. 2. The population subject to food limitation and predation from icthyoplankton (high juvenile mortality) exhibited large size at birth and maturity, large sheath size, and eggs which were relatively large compared to the adult. In contrast, individuals in the population exposed to predation by golden shiner (high adult mortality) were smaller at birth and maturity, had a smaller sheath, and produced relatively small eggs. 3. I contrast body size and relative egg sizes of these H. gibberum populations with literature values for all Cladocera, and propose a general hypothesis for the evolution of relative egg size in Cladocera.