The Mechanism Study On Fluctuation Of Brachionus Calyciflorus Population In Lake Jinghu During Seasonal Alteration Period

The patterns of genetic variation in B. calyciflorus population collected at different dates during seasonal alteration period from Lake Jinghu were studied by allozyme electrophoresis, and their differences in reproductive parameters and life history characteristics at 7℃, 13℃, 19℃, 25℃and 31℃were investigated. The main contents were presented as the following:1. B. calyciflorus collected at different dates during seasonal alteration period from Lake Jinghu were studied by population accumulation culture method at 7℃, 13℃, 19℃, 25℃and 31℃to investigate the difference in productive parameters. The results showed that all rotifers could not survive at 31℃. Between 7 and 25℃, culture temperature, rotifer batch and their interaction all had significant effects on population growth, mixis rate, fertilization rate and resting egg production. There were some differences in responses of productive parameter to increasing temperature among rotifer batches. Except the fifth rotifer batch, the population growth and the mixis rate of other rotifer batches were significantly correlated with the increasing temperatures. Rotifers collected at the end of March had the lowest population growth rate but the highest mixis, fertilizatiom rates and resting egg production.2. Patterns of genetic variation among B. calyciflorus clones collected at different dates during seasonal alteration period from Lake Jinghu were determined using vertical polyacrylamide gel electrophoresis of isoenzymes, and their differences in life history characteristics were investigated. Patterns of PGM enzyme showed no difference among clones, but the GPI and MDH enzymes revealed that variations existed in different batch of rotifer clones, and the relative frequencies of six clones at six collection dates were also different. The effects of temperature on the survivorship and the fecundity of B. calyciflorus differed with rotifer batches, and there were some differences in responses of life history characteristics to increasing temperature among different rotifer batches. Culture temperature, rotifer batch and their interaction all had significant effects on life expectancy at hatching, average lifespan, generation time, intrinsic rate of population increase, net reproductive rate and percentage of mictic females in all the offspring. Except the intrinsic rate of population increase of rotifers at the fifth batch, the life history parameters of rotifers from each collection date were all curvilinearly correlated with culture temperatures.