Phylogenetic relationships of Longidoridae species (Nematoda: Dorylaimida) from North America inferred from 18S rDNA sequence data

A phylogenetic analysis of 18S rDNA sequences was conducted to construct evolutionary trees and evaluate taxonomic relationships among Longidorus and Xiphinema nematode species from North America. A multiple sequence alignment, including Californidorus cylindricaudatus as an outgroup, comprised of 1747 characters of which 1479 were constant, and 146 (8.4 %) were parsimony informative. All sequences had a higher A + T (52.8 %) than G + C composition (47.2 %). Interspecies sequence variation (0.1 % - 9.1 %) was greater than intraspecies sequence variation (0.1 % - 0.6 %). Phylogenetic analysis, using both maximum parsimony and maximum likelihood analysis, revealed three phylogenetically distinct clades representing extant taxonomy, namely, Longidorus, Xiphinema and the X. americanum-group. Within the Longidorus clade, four sub-clades were evident in the maximum likelihood tree. It is concluded that 18S rDNA sequences are appropriate for inferring phylogenetic relationships among longidorid species.