|Stock, S - UNIV CALIFORNIA-DAVIS|
|Nadler, Steven - UNIV CALIFORNIA-DAVIS|
Submitted to: Journal of Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 19, 2001
Publication Date: August 1, 2001
Citation: STOCK,S.P., CAMPBELL,J.F., NADLER,S.A., PHYLOGENY OF STEINERNEMA TRAVASSOS, 1927 (CEPHALOBINA: STEINERNEMATIDAE) INFERRED FROM RIBOSOMAL DNA SEQUENCES AND MORPHOLOGICAL CHARACTERS, JOURNAL OF PARASITOLOGY 87(4): 877-889. 2001. Interpretive Summary: Entomopathogenic nematodes of the genus Steinernema are lethal parasites of insects and are effective biological control agents of some important pests of commercial crops. There is a great deal of diversity within this group of parasites, but how this variation among species evolved was not well understood. Phylogenetic relationships among 21 Steinernema species were estimated using DNA sequences and morphological characters. The results were only partially consistent with previous expectations and indicated that many morphological characters traditionally used for classification were not informative for determining relationships. The results provide a new and comprehensive framework for evaluating the evolution of characters such as search behavior, morphology, pathogenicity, and nematode/bacteria mutualism. Understanding the historical relationships among species within this group is critical for performing and interpreting the species comparison experiments needed to evaluate biological control potential.
Technical Abstract: Entomopathogenic nematodes of the genus Steinernema together with their symbiont bacteria Xenorhabdus, are obligate and lethal parasites of insects that can provide effective biological control of some important lepidopteran, dipteran and coleopteran pests of commercial crops. Phylogenetic relationships among 21 Steinernema species were estimated using 28S ribosomal DNA sequences and morphological characters. Sequences of the rDNA internal transcribed spacers were obtained to provide additional molecular characters to resolve relationships among S. carpocapsae, S. scaterisci, S. siamkayai, and S. monticolum. Four equally parsimonious trees resulted from combined analysis of 28S sequences and 22 morphological characters. Clades inferred from analyses of molecular sequences and combined datasets were primarily reliably supported as assessed by bootstrap resampling, whereas those inferred from morphological ldata alone were not. Although partially consistent with some traditional expectations and previous phylogenetic studies, the hypotheses inferred from molecular evidence, and those from combined analysis of morphological and molecular data, provide a new and comprehensive framework for evaluating character evolution of steinernematids. Interpretation of morphological character evolution on 6 trees inferred from sequence data and combined evidence suggests that many structural features of these nematodes are highly homoplastic, and that some structures previously used to hypothesize relationships represent ancestral character-states.