![]() ![]() However, these DNA markers have not been tested for species identification of ticks. At the same time, 12S rDNA and ITS2 have significantly advanced our understanding of the evolution of ticks. Until now, whether COI is the most suitable DNA marker to discriminate species of ticks is still unknown. Besides, several researches have proved that some DNA fragments were superior to COI in species identification of certain taxa and the amplification of COI from some species often failed. First, the primer pair COI-F/COI-R is not efficient in the recovery of COI from tick specimens second, our previous study only focused on the tree-based method and did not evaluate the efficiency of BLASTn and distance methods, which have proved to give reliable species identification rates finally, compared with the DNA barcoding method based on a single molecular marker, the barcoding system based on three DNA markers was time consuming and noneconomic. However, there are still several problems with this DNA barcoding system. Our previous study has demonstrated that COI and 16S ribosomal DNA (rDNA) were reliable in species identification of ticks and a DNA barcoding system for ticks based on three DNA markers (COI, 16S rDNA, and 18S rDNA) was developed. The 5’ region of the mitochondrial DNA gene cytochrome C oxidase subunit I (COI) is the standard marker for DNA barcoding. ![]() ![]() However, species identification by morphological data can be difficult especially when the specimens are physically damaged, engorged with blood, or in subadult stages (i.e., eggs, larvae, or nymphs). Besides, NN and BLASTn are efficient methods for species identification of ticks.Īccurate identification of species of ticks is important to control tick-borne diseases and has traditionally been achieved through morphological criteria of ticks in adult stage. ConclusionsĪs the standard DNA barcode, COI should be the first choice for tick species identification, while 16S rDNA, ITS2, and 12S rDNA could be used when COI does not produce reliable results. Overall, BLASTn and NN methods produced higher rates of correct species identification than that produced by the liberal tree-based methods (+threshold or otherwise). We also found that COI was not significantly better than the other markers in terms of its rate of correct sequence identification. Our results indicated that the rates of correct sequence identification for all four markers (COI, 16S rDNA, ITS2, 12S rDNA) were very high (> 96%) when using the NN methodology. Genetic divergence analyses showed that the intra-specific divergence of each marker was much lower than the inter-specific divergence. Thereafter, the performance of the four DNA markers to identify tick species was evaluated by identification success rates given by these markers using nearest neighbour (NN), BLASTn, liberal tree-based or liberal tree-based (+threshold) methods. Besides the 1,834 published sequences of 189 tick species from GenBank and the Barcode of Life Database, 430 unpublished sequences representing 59 tick species were also successfully screened by Bayesian analyses. A total of 307 sequences from 84 specimens representing eight tick species were acquired by PCR. In this study, we directly compared the relative effectiveness of COI, 16S ribosomal DNA (rDNA), nuclear ribosomal internal transcribed spacer 2 (ITS2) and 12S rDNA for tick species identification. These deficiencies lead to uncertainty as to whether COI is the most suitable barcoding fragment for species identification of ticks. However, COI has proved to be of limited use in identifying some species, and for some taxa, the coding sequence is not efficiently amplified by PCR. ![]() The 5’ region of cytochrome oxidase I (COI) is the standard marker for DNA barcoding. ![]()
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