Molecular evidence for cryptic species within Cylicostephanus minutus (Nematoda : Strongylidae)

The nucleotide sequences of the first and second internal transcribed space rs of nuclear ribosomal DNA were determined for adults of Cylicostephanus m inutus from different geographical origins. The lengths of first and second internal transcribed spacer sequences ranged from 370 to 372 bp and 215 to 216 bp, respectively. Pairwise sequence comparisons revealed that some ind ividuals of C. minutus had identical first and second internal transcribed spacer sequences, whereas others differed by 3.0% and 7.4% in their first a nd second transcribed spacers, respectively. Some individuals with sequence differences originated from the same host. The levels of difference within C. minutus were higher than that between the morphologically distinct spec ies, Cylicostephanus goldi and Cylicostephanus longibursatus (0.8% for the first internal transcribed spacer and 3.8% for the second internal transcri bed spacer). The data provide support for the proposal that C. minutus repr esents a complex of at least two species. In order to study the population genetic structure of C. minutus, a PCR-linked single-strand conformation po lymorphism technique was also established. (C) 1999 Australian Society for Parasitology. Published by Elsevier Science Ltd. All rights reserved.