Stepwise and Canonical Discriminant Analysis of Longidorus Species (Nematoda: Longidoridae) from Arkansas

Abstract

During a 1998-to-2001 survey from Arkansas, nine distinct species of Longidorus were found including five new species. Morphometrics of these nine species were used in a stepwise and canonical discrimination to select a subset of characteristics that best identified each species. Student's t test was applied to compare Longidorus breviannulatus Norton & Hoffman, 1975; L. crassus Thorne, 1974; L. diadecturus Eveleigh & Allen, 1982; L. fragilis Thorne, 1974; L. biformis Ye & Robbins, 2004; L. glycines Ye & Robbins, 2004; L. grandis Ye & Robbins, 2003; L. paralongicaudatus Ye & Robbins, 2003; and L. paravineacola Ye & Robbins, 2003 to examine interspecies variation and test for the most useful morphometric characters in species discrimination. Most of the morphometric characters were useful to differentiate species, but species identification could not be based on a single character because the morphometric character ranges often overlap. Stepwise discriminant analysis indicated that the guide ring position, head width, tail length, body length, odontostyle length, and anal body width were the most important variables. These were used to generate canonical variables in discriminating the species. The first three canonical variables accounted for 95% of the total variance. The scatterplots by the first three canonical variables grouped and separated the Longidorus species from Arkansas. Stepwise and canonical discriminant analyses were useful for examining the groupings and morphometric relationships of the nine Longidorus species.