Ticks (order Ixodida) are ectoparasites, vectors, and reservoirs of many infectious agents affecting humans and domestic animals. However, the lack of information on tick genomic diversity leaves significant gaps in understanding the evolution of ticks and associated bacteria.
We collected > 20,000 contemporary and historical (up to 60 years of preservation) tick samples representing a wide range of tick biodiversity across diverse geographic regions in China. Metagenomic sequencing was performed on individual ticks to obtain the complete or near-complete mitochondrial (mt) genome sequences from 46 tick species, among which recovered mitochondrial genomes of 23 species for the first time. These new mt genomes data greatly expanded the diversity of many tick groups and revealed five cryptic species.
We identified divergent and abundant bacteria in Haemaphysalis, Ixodes, Dermacentor, and Carlos ticks, including nine pathogenetic bacteria.
We also used these data to explore the evolutionary relationship between ticks and their associated bacteria, revealing a pattern of long-term co-divergence relationship between ticks and Rickettsia and Coxiella bacteria.
In sum, our study provides important new information on the genetic diversity of ticks based on an analysis of mitochondrial DNA and the prevalence of tick-borne pathogens in China.
It also sheds new light on the long-term evolutionary and ecological relationships between ticks and their associated bacteria.