Water flea Daphnia pulex in Japan has 4 lineages. They are the same species but genetically isolated each other due to the obligate parthenogenesis. In this project, whole-genome sequencing data of Japanese populations of D. pulex were analyzed to examine how the lineages differ in each region of the genome. Based on the sequence data, Each genotype was classified into 4 groups similar to a previous study. The data also suggested that the lineage arrived in Japan later would not yet be subjected to negative selections than the lineage arrived earlier.