| Brachionus calyciflorus is among the cosmopolite species of freshwater rotifers. It plays an important role in the material cycle and energy transportation of freshwater ecosystem. Furthermore, it was found quite valuable in aquaculture and environmental monitoring. This article concentrated on the effect of food concentration on the initiation and the life history traits of micitc females in B. calyciflorus, as well as the comparative study on the mating behavior and fertilization of mictic females in two strains. The main contents were presented as the following: 1. The effects of food concentration on the initiation of mictic females in the B. calyciflorus populations were studied by means of population accumulative culture. The results showed that when the food concentration was 2.0 ×10~6cells/mL, 5.0×10~6cells/mL and 8.0×10~6cells/mL, the emerging time of male egg-producing mictic females, males and resting egg-producing mictic females were 0.5, 1.5 and 2d,0.5, 1.5 and 3d, and 0.5, 1, and 1.5d, respectively. During the 10-day-culture, the mean density and the production of amictic females and male egg-producing mictic females were both the highest at the food concentration of 8.0×10~6cells/mL, while no significant differences appeared when the food concentration was 2.0×10~6cells/mL and 5.0×10~6cells/mL. The mean density and the production of resting egg-producing mictic females appeared to be the lowest at 2.0×10~6cells/mL, with no significant differences between the other two food concentrations. No significant differences in the mean density and the production of males were observed among food concentrations. The M/T ratio reached its maximum at 2.0×10~6cells/mL, with no significant difference between the other two food concentrations. The mean mixis rate at 8.0×10~6cells/mL was the lowest, while those at 2.0×10~6cells/mL and 5.0×10~6cells/mL were higher. The mean fertilization rate increased when food concentration was higher. 2. The mating behavior and fertilization of Qingdao and Wuhu strains in B. calyciflorus were studied, and the results showed that the mating behaviors of inter-and intra-strains were almost the same. In addition, there were no significant differences between their mating durations. The sex ratio (male/female) affected the fertilization rate of the mictic females of Qingdao strain significantly, while did not affect that of Wuhu strain. There was no significant difference in the fertilization rates of two strains at the sex ratio 1:4, 1:2 and 4:1. When the sex ratio was 1:1 and 2:1, however, the fertilization rates of Qingdao strain were significantly higher than those of Wuhu strain. The fertilization rate of mictic females in Wuhu strain declined non-linearly with their aging from 4h to 16h. By age 12h, all mictic females could no longer be fertilized. The LF50 (age at which 50% mictic females in a population was fertilized) of the mictic females of Wuhu strain was 5.32h. The fertility of males from Wuhu strain also declined non-linearly with their aging. The LF50 was 15.05h. 3. Life history traits of unfertilized mictic females (UMF) and fertilized mictic females (FMF) in two strains of the freshwater rotifer B. calyciflorus obtained from Qingdao and Wuhu cities of China and cultured at three different algal concentrations (2.0, 5.0 and 8.0×10~6 cells/mL) were compared. Food concentration significantly affected the duration of the post-reproductive period and the egg volume of UMF as well as the duration of the pre-reproductive period, the egg volume, and the reproductive investment of FMF of the Qingdao strain. Food concentration also influenced the pre-reproductive period, the mean life span, the egg volume, and the reproductive investment of UMF and FMF of the Wuhu strain. At some food concentrations, there were also significant differences in many life history characteristics between the two rotifer strains.
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