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

• Sequence variation in cox1, nad1, nad4 and rrnS among and within four Contracaecum species was investigated.
• Intra-specific variation was 0–2.6%, 0.3–2.5%, 0–1.9% and 0–2.9% for these mtDNA sequences respectively.
• Inter-specific difference was 3.3–12%, 9.8–15.2%, 9.6–18.3% and 3.5–11.12% for these sequences respectively.
• Provided additional genetic evidence for the existence of 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 pcox1, pnad1, pnad4 and prrnS, 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 pcox1, 0.3–2.5% for pnad1, 0–1.9% for pnad4 and 0–2.9% for prrnS, 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 pcox1, pnad1, pnad4 and prrnS 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.