Genetic variation in three mitochondrial genes among cattle tick Rhipicephalus microplus originating from four...

The cattle tick, Rhipicephalus microplus (formerly Boophilus microplus), is the most important blood-feeding ectoparasite of cattle in tropical and subtropical regions of the world. In this study, we examined sequence variability in three mitochondrial (mt) DNA (cox1, nad1, nad4) among cattle tick R. microplus originating from four provinces of China. A portion of cox1 (pcox1), nad1 (pnad1) and nad4 (pnad4) genes were amplified by polymerase chain reaction (PCR) separately from adult R. microplus individuals and the amplicons were subjected to sequence from both directions. The sequence of mt cox1, nad1, nad4 genes was 817 bp, 350 bp, and 794 bp in size, respectively. The intraspecific sequence variations within R. microplus were 0-8.6% for cox1, 0-4.9% for nad1 and 0-10.3% for nad4. However, the interspecific sequence differences among the members of the Rhipicephalus [R. sanguineus (JX416325) and R. turanicus (NC035946)] were significantly higher, being 16.9-20.5%, 18- 22.8%, 22.8-25.3% for pcox1, pnad1 and pnad4, respectively. In addition, genetic differences were 7.9-8.6% for cox1, 4.3-4.9% for nad1 and 10-10.3% for nad4 between the two detected lineages (R. microplus clade A and clade B). Phylogenetic analyses indicated that all the Rhipicephalus isolates from the present study represents R. microplus, supporting that R. microplus represents species complex. Our result provided an additional genetic evidence for the existence of species complex within R. microplus in China.