A phylogenetic analysis of Heterorhabditis (Nemata : Rhabditidae) based oninternal transcribed spacer 1 DNA sequence data

Internal transcribed spacer 1 sequences were used to infer phylogenetic rel ationships among 8 of the 9 described species and one putative species of t he entomopathogenic nematode genus Heterorhabditis. Sequences were aligned and optimized based on pairwise genetic distance and parsimony criteria and subjected to a variety of sequence alignment parameters. Phylogenetic tree s were constructed with maximum parsimony, cladistic, distance, and maximum likelihood algorithms. Our results gave strong support for four pairs of s ister species, while relationships between these pairs also were resolved b ut less well supported. The ITS1 region of the nuclear ribosomal repeat was a reliable source of homologous characters for resolving relationships bet ween closely related taxa but provided more tenuous resolution among more d ivergent lineages. A high degree of sequence identity and lack of autapomor phic characters suggest that sister species pairs within three distinct lin eages may be mutually conspecific. Application of these molecular data and current morphological knowledge to the delimitation of species is hindered by an incomplete understanding of their variability in natural populations.