Complete Mitochondrial Genome Sequence Data Provides Genetic Evidence That the Brown Dog Tick Rhipicephalus sanguineus (Acari: Ixodidae) Represents a Species Complex

Ticks are blood-sucking ectoparasites of great medical and veterinary significance that can transmit bacteria, protozoa, fungi and viruses, and cause a variety of human and animal diseases worldwide. In the present study, we sequenced the complete mitochondrial (mt) genome of Rhipicephalus sanguineus from China (RSC) and compared with that of R. sanguineus from USA (RSU). Nucleotide sequence difference in the full mt genome was 11.23% between RSC and RSU. For the 13 protein-coding genes, comparison revealed sequence divergences at both the nucleotide (9.34-15.65%) and amino acid (2.54-19.23%) levels between RSC and RSU. In addition, sequence comparison of the conserved mt cox1 and cytb genes among multiple individual R. sanguineus revealed substantial nucleotide differences between RSC and RSU but limited sequence variation within RSC. Phylogenetic analysis of ticks based on the amino acid sequence data of 13 protein-coding genes revealed that R. sanguineus from China and R. sanguineus from USA represent sister taxa (likely separate species). Taken together, the findings support the recently proposal that R. sanguineus tick may represents a species complex of at least two closely related species.