The first internal transcribed spacer (ITS-1) of ribosomal DNA as a molecular marker for phylogenetic and population analyses in Crustacea

The objective of the present study is to explore the feasibility of using t he first internal transcribed spacer (ITS-1) of ribosomal DNA as a molecula r marker for studying the interspecific and intraspecific genetic variation s among crustaceans. We designed primers that could amplify ITS-1 from a ma jority of taxonomic groups of crustaceans. The gene was found to exhibit a high degree of length polymorphism among different groups, ranging from 182 bp in the barnacle Balanus amphitrite to approximately 820 bp in the spiny lobster Panulirus japonicus. With respect to differences between congeneri c species, it was found that the ITS-1 sequences of 3 mitten crabs, Erioche ir sinensis, Eriocheir leptognathus, and Eriocheir formosa, exhibit 5.4% to 16.3% nucleotide divergence, suggesting that ITS-1 is informative for phyl ogenetic analysis at the species level. Yet there are extensive (0.9%-2.3%) variations within individual E. formosa, so that phylogenetic analyses cou ld be obscured. ITS-1 was found to vary between 2 geographical populations of the shrimp Penaeus japonicus. The variations involved substitutions as w ell as insertions/deletions between shrimp from Australia and South China S ea. These results show that ITS-1 is highly divergent among different crust aceans and could be an appropriate marker for molecular systematic studies at the species and population levels, although the presence of intragenomic variation needs to be taken into consideration.