| Brachionus calyciflorus is a common specie in freshwater ecosystem, and has important status in structure construction, material cycle and energy transportation in freshwater ecosystem. Three isozyme including gloucose phosphate isomerase (GPI), malica dehydrogenase (MDH) and phosphoglucomutase (PGM) were selected, and vertical polyacraylamide gel electrophoresis was used to screen the B. calyciflorus population collected in spring and summer from Lake Jinghu, and the life history characteristics of thirteen genetically different B. calyciflorus clones were studied at four different temperatures. The main contents and results were presented as the following:1 Three isozyme including gloucose phosphate isomerase (GPI), malica dehydrogenase (MDH) and phosphoglucomutase (PGM) were selected, and vertical polyacraylamide gel electrophoresis was used to screen the B. calyciflorus population collected in spring and summer from Lake Jinghu. Patterns of GPI and MDH enzymes revealed variations existed in the two seasonal populations. Six different clonal groups from the spring population and seven different ones from the summer population were identified by combing isozymes variations. Two clonal groups with same genotype existed in the spring and the summer populations. The frequency of the same genotype in the rotifer population differed with season. The results of reproductive experiments made at 15℃, 20℃, 25℃and 30℃on thirteen clones representing different composite electromorphs in spring and summer collections showed that the responses in growth rate, mictic rate, fertilization rate and resting egg production of rotifers to increasing temperature were different among thirteen clones, and temperature, genotypes and their interaction all affected significantly growth rate, mictic rate, fertilization rate and resting egg production, which might be one of reasons that contribute to maintain the high genetic variations in the rotifer population. The results stated above indicated that the genetic structures of B. calyciflorus population in Lake Jinghu differed with season, and the ecological characteristics including rate of asexual reproduction (with the population growth rate as an endpoint), and occurrence, course and result of sexual reproduction - formation and fertilization of mictic females, and resting egg production of B. calyciflorus population differentiated between two seasons.2 By means of life table demographic approach, life-table demographic parameters and percentage of micitc females in the offspring of thirteen genetically different B. calyciflorus clones were studied on at 15℃, 20℃, 25℃and 30℃. The results showed that responses of generation time, average lifespan, life expectancy at hatching, net reproductive rate, intrinsic rate of population increase and percentage of micitc females in the offspring of B. calyciflorus to increasing temperature differed with rotifer clones. Temperature, clone and their interaction influenced significantly the life-table demographic parameters and the percentage of micitc females in the offspring of B. calyciflorus. The results stated above indicated that temporal heterogeneity of temperature in water environment may be one of the reasons that account for high genetic variations in B. calyciflorus population from Lake Jinghu. Natural selection occurred in coexisting clones, but might be either too weak or too limited a duration for clonal exclusion to occur. Genetic drift might play an important role in genotype frequency variation. The coexistence of clones with different genotypes in nature took an important significance for the existence of B. calyciflorus population in water environment.3 The neonate starvation times of thirteen genetically different B. calyciflorus clones were studied at 15℃, 20℃, 25℃and 30℃, and the relationships between the neonate starvation time and body volume, egg volume as well as neonate volumes were analyzed. The results showed that responses of the neonate starvation, and body, egg and neonate volumes in the offspring of B. calyciflorus to increasing temperature differed with rotifer clones. Temperature, clone and their interaction influenced significantly the neonate starvation, and body, egg and neonate volumes in the offspring of B. calyciflorus. The neonate starvation times of all the thirteen clones were curvilinearly correlated with temperature. The neonate starvation times of Clone SP1 was negatively correlated with body volumes. The neonate starvation times of Clone SP2 was negatively correlated with neonate volumes, but that of Clone SU1, SU3 and SU7 were positively correlated with neonate volumes. The results stated above indicated that temperature and clone genotype affected significantly offspring quality and led to frequencies of the clones changed in the future population.
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