DIFFERENCES IN A RIBOSOMAL DNA-SEQUENCE OF LUNGWORM SPECIES (NEMATODA, DICTYOCAULIDAE) FROM FALLOW DEER, CATTLE, SHEEP AND DONKEYS

The second internal transcribed spacer (ITS2) of the ribosomal DNA of Dictyocaulus viviparus from cattle, D eckerti from fallow deer, D Fil aria from sheep and D arnfieldi from donkeys has been sequenced to inv estigate the genetic relationships among lungworm species, especially between D viviparus and D eckerti, because the latter is not generally accepted as a separate species. The length of the ITS2 varied between 403 and 481 bases, and its GC content ranged from 25 to 33 per cent. Intraspecific variations in D viviparus (0 to 1.5 per cent) and D ecke rti (0.6 to 3.3 per cent) were slight; sequence homology between the s pecies ranged from 50.3 to 76.7 per cent. Some sequence differences oc curred at restriction sites of endonucleases leading to characteristic restriction fragment length patterns. The interspecific differences b etween D viviparus and D eckerti far exceeded the intraspecific variat ion, thus providing additional evidence that the two species are genet ically distinct.