How a new population establishes in a novel habitat has been an important question of ecology. Understanding the temporal change of population genetic structure is important to consider ecological and evolutionary process in establishment, although its direct observation is difficult. Here, we tried to reveal the genetic dynamics of obligate parthenogenetic Daphnia pulex population from its early establishment using their dormant eggs enclosed in ephippia preserved in the varved sediment.
　In lake Fukami-ike, Nagano, we collected lake sediment core samples and counted the ephippia to examine population dynamics. We analyzed the genetic structure based on 1628 bp of mtDNA. In addition, we measured morphological traits of ephippia and subfossils to examine the change of phenotype.
　D. pulex established a firm population in early 2000s. While we detected 13 genotypes, one genotype was dominant throughout the study period. Both of haplotype richness and diversity showed genetic structure composed by limited genotypes and suggested no trend of increasing genetic diversity. These results suggest that the priority effect and no clonal turnover was observed in this obligate parthenogenetic population. Contrary to limited genetic diversity, the morphological analysis suggested that size and time to maturity possibly changed in response to the change of predation.