Characterization of the complete mitochondrial genome of Haemaphysalis hystricis and its phylogenetic implications.

Abstract

Haemaphysalis hystricis is a medically important tick vector, and three complete mitochondrial genomes derived from specimens collected from different geographic regions and hosts have previously been reported. In this study, we sequenced and analyzed the complete mitochondrial genome derived from H. hystricis specimens collected from a human host in Shaoguan, Guangdong Province, China, and systematically compared it with previously published H. hystricis mitogenomes. The complete mitogenome is 14,714 bp in length and contains 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes, and two non-coding control regions. The overall gene order and composition are highly conserved and consistent with those reported for other Haemaphysalis species. The genome exhibits a strong A + T nucleotide bias, which is a typical feature of hard tick mitogenomes. Most tRNAs fold into typical cloverleaf secondary structures, whereas several exhibit truncated structures, reflecting a common pattern of mitochondrial tRNA structural simplification in arthropods. Selective pressure analysis indicated that all 13 PCGs are under purifying selection. Maximum-likelihood phylogenetic analysis showed that H. hystricis was most closely related to H. longicornis, consistent with previous studies. This study provides an additional H. hystricis mitogenome and compares it with the three previously published conspecific mitogenomes. The comparison revealed differences in genome length, the structure of non-coding regions, and tRNA secondary structures and provided estimates of gene-specific selective pressures. These findings provide valuable data for comparative mitogenomics and studies of intraspecific genetic variation in ticks.