Sequence variation in four mitochondrial genes among sibling species within Contracaecum rudolphii sensu lato

The present study investigated sequence variability in four mitochondrial DNA (mtDNA) regions, namely cytochrome c oxidase subunit (cox1), NADH dehydrogenase subunits 1 and 4 (nad1 and nad4), and small subunit of rRNA (rrnS), among Contracaecum rudolphii A, C.rudolphii B, C.rudolphii C and Contracaecum septentrionale from different hosts and geographical origins in China, Italy, Spain and the USA. Regions in the cox1, nad1, nad4 and rrnS genes (designated p. cox1, p. nad1, p. nad4 and p. rrnS, respectively) were amplified separately from individual nematodes by PCR, sequenced and compared to estimate sequence variability. While sequence variation within each of the Contracaecum species was 0-2.6% for p. cox1, 0.3-2.5% for p. nad1, 0-1.9% for p. nad4 and 0-2.9% for p. rrnS, differences between species was significantly higher, being 3.3-12%, 9.8-15.2%, 9.6-18.3% and 3.5-11.12% for these regions, respectively. Phylogenetic analyses of p. cox1, p. nad1, p. nad4 and p. rrnS sequence data using maximum likelihood (ML), maximum parsimony (MP) and neighbour joining (NJ) showed that the specimens of each Contracaecum species clustered together. These results provide additional genetic evidence for the existence of sibling species within C.rudolphii sensu lato. © 2013 Elsevier Ltd.