Relationships among some ascaridoid nematodes based on ribosomal DNA sequence data

Abstract

The nuclear ribosomal DNA (rDNA) region spanning the first (ITS-1) and second (ITS-2) internal transcribed spacers was sequenced for 15 taxa of ascaridoid nematodes. The length of the ITS-1 and ITS-2 sequences in the 15 taxa ranged from 392–500 bp and 240–348 bp, respectively. While nucleotide variation of 0–2.9% in the ITS-1 and/or ITS-2 sequences was detected within taxa where multiple samples were sequenced, significantly higher level of nucleotide difference (9.4–66.6%) was detected between the taxa, except for Ascaris suum and A. lumbricoides whose taxonomic status remains uncertain. These interspecific differences were linked with the considerable size differences (0–108 bp) in the rDNA spacers. Phenograms based on the genetic differences among the 15 taxa showed some concordance with previous classification schemes derived from morphological data.