SEASONAL VARIATIONS IN EGG SIZE, BROOD SIZE AND BODY LENGTH OF CERIODAPHNIA RETICULATA (CRUSTACEA: CLADOCERA) FROM LAKE IKEDA, JAPAN

Monthly samplings were made at a fixed station in Lake Ikeda, a deep crater lake in order to follow the seasonal variations in egg size, brood size and body lengths of ovigerous Ceriodaphnia reticulata, which is one of the main cladoceran species inhabiting this lake. Results of monthly samplings showed that Ceriodaphnia reticulata in summer matured at relatively small body sizes and carried smaller eggs, which produced smaller individuals. However, in autumn these individuals began to produce bigger eggs that upon hatching produced relatively bigger individuals until winter. In spring, these bigger individuals began to produce relatively smaller eggs that on hatching gave rise to smaller individuals until summer. Bigger ovigerous females were able to carry more eggs than smaller counterparts. Brood size was inversely related to egg size.