Abstract: In this article, the ribosomal 18S and the second internal transcribed spacer (ITS2)sequences of the Daphniopsis tibetana Sars were amplified and the evolutionary status were investigated. The results showed that the length of 18S rDNA sequence was 2296 bp, the contents of A, T (U), G and C were 21.2%, 24.4%, 29.8% and 24.6%, respectively, the average length of ITS2 sequence was 1229 bp, while the contents of A, T (U), G and C were 28.3%，23.5%，25.5%，22.7%, respectively. The phylogenetic tree was constructed with the maximum likelihood method (ML)by MEGA5.0 software. It is showed that the genetic relationship between D. tibetana and D. quadrangula was so closest to clustere in the same branch. However, D. tibetana and Daphnia magna were clustered on different branches. It is confirmed that D. tibetana should be classified in the Daphniopsis genus, which is consistent with the previous studies. Compared with 18S rDNA, there were differences in base and length among the ITS2 sequences in D. tibetana. The divergence were obvious among the same family but different genera. The 18S rDNA and ITS2 sequences obtained from this study provide the basic data for the further molecular studies of D. tibetana.

Key words: Daphniopsis tibetana, 18S rDNA, ITS2, genetic distance, phylogenetic analysis