Sequence variations of the first ribosomal internal transcribed spacer of Penaeus species in Thailand

The ribosomal DNA internal transcribed spacer 1 (ITS1) was investigated in the search for additional genetic marker that is suitable for population studies of the penaeid shrimps. The sequence variations of the ITS1 were determined and found to be informative in estimating phylogenies in that they differentiate four species of penaeid shrimps, namely Penaeus merguiensis, Penaeus silasi, Penaeus monodon and Penaeus semisalcatus and the populations of P. merguiensis collected in the Gulf of Thailand and the Andaman Sea. The length of the ITS1 ranged from 499 to 772 bp, with a GC content of 63.30-67.37%. Four microsatellite loci are found in the ITS1 at 5′ end and the middle of region and seem to be associated with sequence divergence and size variation in Penaeus species. Some microsatellites were found in only one specie, (GCGA)₄ in P. semisalcatus and (CGGA)_4-9 in P. monodon. These microsatellite regions are considerably long enough and the level of intragenomic variation in P. merguiensis is less than that between different species, hence, provide a great potential use in the population studies.