Hydra is a well-known fresh water cnidarian polyp that usually reproduces asexually by budding. And its locomotion activity is low because it does not have the medusa type. These features make understanding of the genetic structure of hydra populations an intriguing issue. Therefore, we studied genetic structure of populations of Hydra magnipapillata, a common hydra in Japan, based on analyses of two mitochondrial and 11 microsatellite loci.

We collected 302 individuals of H. magnipapillata from 25 ponds in Fukuoka and Hyogo prefectures. We also obtained 16 strains originating from other places in the Hydra strain collection of the National Institute of Genetics of Japan. Our microsatellite analysis revealed that each population of hydra consisted of only one genotype though two or three genotypes were detected in a few ponds. This suggested that hydras mostly gave rise to a clonal population in a pond. Furthermore, some clones were observed in multiple ponds, so that geographic limits of clonal populations could be extended over ponds.

Based on the results, we discuss genetic structure of populations in H. magnipapillata and the evolutionary process in hydra populations. Our data also may contribute to understand processes of colonization in clonal organisms.