Department of Integrative Biology

DNA sequence divergence at internal transcribed spacer regions (ITS-1 and ITS-2) was compared with divergence at mitochondrial coxl or nad4 loci in pairs of congeneric nematode species. Mitochondrial sequences accumulate substitutions much more quickly than internal transcribed spacer, the difference being most striking in the most closely related species pairs. Thus, mitochondrial DNA may be the best choice for applications in which one is using sequence data on small numbers of individuals to search for potential cryptic species. On the other hand, internal transcribed spacer remains an excellent tool for DNA diagnostics (quickly distinguishing between known species) owing to its lower level of intraspecific polymorphism. (C) 2002 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.