Complete Mitogenome of Haemaphysalis parva Tick Unveiled, Revealing Unique Evolutionary Markers

Ticks are significant vectors for various pathogens, including bacteria, viruses, and protozoa, posing a substantial threat to human and animal health worldwide. Understanding their mitogenomes (the complete genetic material of their mitochondria) provides crucial insights into their evolution, population genetics, and potential for disease transmission. However, comprehensive mitogenomic data for many Haemaphysalis species, particularly less-studied ones like Haemaphysalis parva, remains limited, hindering robust comparative genomic analyses and phylogenetic studies.

The study successfully sequenced the complete mitogenome of Haemaphysalis parva, revealing a circular molecule of approximately 15,500 base pairs (bp). This mitogenome was found to contain the typical 37 genes: 13 protein-coding genes (PCGs), 2 ribosomal RNA (rRNA) genes, and 22 transfer RNA (tRNA) genes, all arranged on the heavy strand. The overall A+T content was notably high at 78.2%, a characteristic often observed in tick mitogenomes, indicating specific evolutionary pressures. The most significant finding was the identification of a unique gene arrangement in H. parva compared to other Haemaphysalis species, particularly a novel translocation of the tRNA-Leu gene from its ancestral position, which could serve as a robust phylogenetic marker. Comparative analysis showed 90-95% sequence identity for highly conserved genes like cox1 (cytochrome oxidase subunit 1) and nad5 (NADH dehydrogenase subunit 5) across the genus, but significant divergence in non-coding regions and gene order, indicating distinct evolutionary pressures and lineage-specific adaptations. Phylogenetic trees constructed using the complete mitogenome sequences provided strong statistical support (bootstrap values >95%) for the monophyly of Haemaphysalis and clarified its relationship with other Ixodidae families.