A COMPARISON OF THE FIRST INTERNAL TRANSCRIBED SPACER OF RIBOSOMAL DNA IN 7 SPECIES OF TRICHOSTRONGYLUS (NEMATODA, TRICHOSTRONGYLIDAE)

The first internal transcribed spacer (ITS-1) of the ribosomal DNA of seven species of Trichastrongylus was sequenced. The length of ITS-1 i n the different species varied from 387 to 390 bases. The G+C content of the ITS-I sequences were approximately 42%. Little or no intraspeci fic variation was detected in the three species, Trichostrongylus axel , Trichastrongylus colubriformis and Trichostrongylus vitrinus, for wh ich multiple isolates from different geographical regions were sequenc ed. In contrast, the level of ITS-1 sequence differences between speci es ranged from 1.3% to 5.7%. The greatest sequence differences were de tected between T. tenuis, the parasite species which infects birds and the six species found in mammals. Some of the nucleotide differences occurred at sites corresponding to recognition sites for restriction e ndonucleases. These results are compared with previous data obtained f or the second internal transcribed spacer (ITS-2). The ITS-1 data indi cate that this region of rDNA may also be useful for systematic studie s in trichostrongylid nematodes. (C) 1998 Australian Society for Paras itology. Published by Elsevier Science Ltd.