Global genetic structure and demographic history of Haemaphysalis longicornis revealed by mitochondrial cytochrome c oxidase subunit I sequences.

BACKGROUND

Haemaphysalis longicornis is an important vector of multiple tick-borne pathogens and exhibits both parthenogenetic and bisexual reproductive modes. Among them, the parthenogenetic strain has spread to North America and Oceania. However, a systematic comparison of the genetic structure, dispersal patterns, and demographic history between the parthenogenetic and bisexual strains is still lacking.

METHODS

Global mitochondrial cytochrome c oxidase subunit I (COI) sequences of H. longicornis were retrieved from GenBank. Phylogenetic reconstruction, Bayesian genetic clustering, haplotype network analysis, genetic differentiation analysis, Mantel tests, and demographic analyses were performed to compare the genetic structure, dispersal patterns, and demographic history of the parthenogenetic and bisexual strains.

RESULTS

A total of 1147 sequences were included, including 703 sequences from the parthenogenetic strain and 444 from the bisexual strain. The two strains shared no haplotypes and exhibited strong genetic differentiation (FST=0.902). The parthenogenetic lineage comprised three major genetic clusters, indicating multiple source populations and independent dispersal events, whereas the bisexual lineage formed a single genetic cluster and remained largely restricted to East Asia. Although both strains showed genetic signatures of population expansion, their demographic histories differed markedly: the parthenogenetic lineage fitted the sudden expansion model, whereas the bisexual lineage deviated from this model.

CONCLUSION

The parthenogenetic and bisexual strains exhibit markedly different genetic structures, geographic distributions and demographic histories. The parthenogenetic lineage appears to be the principal lineage involved in trans-regional spread and invasion, whereas the bisexual lineage remains largely confined to its native range in East Asia.