Mitochondrial genome analysis reveals intraspecific variation within Australian hard tick species

Abstract

Ticks rank second in the world as vectors of disease so it is paramount we understand their biology in order to advance disease control. Mitochondrial genome sequences of tick species have been used increasingly to resolve relationships of closely related species, correct taxonomic discrepancies and to understand intraspecific variation. Despite this, our understanding and advances in tick biology are obstructed by the lack of complete mitochondrial genomes available for most species, particularly amongst Ixodidae ticks that are highly prevalent and taxonomically diverse. Even fewer have more than one representative genome sequence meaning that answering questions over intra-species variation is rarely possible. Here, we present the adult tick mitochondrial genomes of two species which had not previously been sequenced, H. bancrofti and I. tasmani, as well as multiple representatives for both adult I. holocyclus and I. tasmani. Complete mitochondrial genomes were used to investigate the intraspecific variation within geographically dispersed I. tasmani ticks as well as I. holocyclus ticks parasitising different host species. Although sample sizes were limited, I. tasmani diversity appeared to be influenced by geography, while the genetic diversity observed in I. holocyclus was not influenced by host or geography. This genetic resource will support downstream studies into the population genetics of Australian hard ticks and inform efforts to expand this work to other Australian tick species. To build an appropriate repertoire, future analyses should include Australian tick species that are yet to be genome sequenced, particularly those that carry pathogens while including multiple representatives of each species.