Temporal Variation Of Structure Of Brachionus Calyciflorus Complex In Lake Tingtang During Winter And Spring And Ecological Mechanism

By molecular biological methods including COI gene amplification,sequencing and analyses, life table demography and competition ability tests,temporal variation of structure of Brachionus calyciflorus complex and ecologicalmechanism were investigated. The main results were presented as the following:1. Individuals of B. calyciflorus were collected once a week from LakeTingtang during early December2011and mid-April2012, and clonally cultured.Their COI genes were sequenced and analyzed. In total of257samples,148haplotypes were defined, among which2distinct lineages (Lineages I and II) wererevealed by phylogenetic analysis. Sequence divergence was18.1-19.5%betweenthe two lineages, indicating the occurrence of two sibling species (sibling speciesT3and sibling species T4). Sibling species T3occurred throughout the winter andspring, and its relative abundance in the density of the species complex was higher;sibling species T4occurred only during February21and March26. Some clones ofBrachionus calyciflorus showed overlap, but the others showed displacement.2. The life table demographic parameters of sibling species T3and siblingspecies T4were calculated at16℃,20℃,24℃and28℃, and with1.0×10~6,3.0×10~6and5.0×10~6cells/ml of Scenedesmus obliquus as food. The results showedthat temperature and sibling species affected significantly all life table demographicparameters (P<0.05), the interaction between temperature and sibling speciesaffected the net reproductive rate and intrinsic rate of population increase (P<0.05),and the interaction between temperature and food level affected the intrinsic rate ofpopulation increase of the rotifers (P<0.05). Life expectancy at hatching,generation time, average lifespan, net reproductive rate, intrinsic rate of populationincrease and proportion of sexual offspring of sibling species T3were higher thanthose of sibling species T4, which might be one of the main reason for that therelative abundance of sibling species T3was higher than that of sibling species T4.3. The competition ability of sibling species T3and sibling species T4were testted at16℃and24℃, and with0.1×10~6、0.5×10~6、1.0×10~6、2.0×10~6、4.0×10~6and6.0×10~6cells/ml of S. obliquus as food. The results showed that at16℃and24℃, TFL (threshold of food level) values of sibling species T3were significantlylower than those of sibling species T4(P<0.05), and so the competition ability ofsibling species T3was significantly higher than that of sibling species T4, whichmight be another of the main reason for that the relative abundance of siblingspecies T3was significantly higher than that of sibling species T4.