PHYLOGENETIC-RELATIONSHIPS OF ENTOMOPATHOGENIC NEMATODES (HETERORHABDITIDAE AND STEINERNEMATIDAE) INFERRED FROM PARTIAL 18S RIBOSOMAL-RNA GENE-SEQUENCES

Aligned 265-bp sequences of partial 18S rRNA gene were used to infer p hylogenetic relationships among entomopathogenic nematodes by using ma ximum parsimony and likelihood methods. Phylogenetic analyses support Heterorhabditidae and Steinernematidae belonging to different monophyl ies. There was more sequence divergence in Steinernema species than in Heterorhabditis species. These results are congruent with the phyloge nies based on morphological, life cycle, and distributional evidence. Examination of all trees within 1% of the length of the most parsimoni ous trees and bootstrap analyses support most relationships among Stei nernema species but the relationships among Heterorhabditis species we re not supported. We suggest that the partial 18S rRNA gene sequences may be too conserved for phylogenetic inference among Heterorhabditis species, but are well suited for phylogenetic inference within and amo ng closely related families and genera of entomopathogenic nematodes a nd for inferring phylogenetic relationships among Steinernema species. (C) 1997 Academic Press.