Investigation into the Distribution and Bacterial Microbiome of Rhipicephalus Sanguineus Sensu Lato Lineages in Arizona

Abstract

Rhipicephalus sanguineus s.l. (Latreille, 1806), the brown dog tick, is the most widely distributed tick species in the world. The two dominant lineages, a temperate group and a tropical group, are recognized as important disease vectors for both dogs and humans. This research examines the distribution and bacterial composition of the temperate and tropical lineages of R. sanguineus s.l. across the state of Arizona, where outbreaks of Rocky Mountain spotted fever are linked to the tick species complex. The geographical ranges of the temperate and tropical lineages were well delineated, with some overlap in the eastern part of the state and evidence of the two lineages in sympatry on the same host. In evaluating the tick’s bacterial community, I detected 37 strains of R. sanguineus s.l.’s obligate maternally-inherited bacteria, Coxiella-like endosymbionts (CLEs), with two strains accounting for the vast majority of 16S rRNA amplicon reads. One strain strongly associated with the tropical lineage of R. sanguineus s.l. while the other was found almost exclusively in the temperate lineage, supporting the conclusion that CLEs are primarily vertically transmitted. However, occasional mismatchesbetween tick lineage and symbiont SV indicate that horizontal symbiont transfer may occur, perhaps via co-feeding of ticks from different lineages on the same dog. I used a blocking primer to prevent sequencing of Coxiella to enable a closer examination of bacterial community structure. While I found many commonalities among bacterial genera found within R. sanguineus s.l. ticks across the state, there were no clear patterns in bacterial community composition based on lineage, sex, female engorgement level, or collection location. While it is unclear to what extent they may differ in their capacity to transmit certain pathogens, this research elucidates otherwise unexplored aspects of the ecology and biology of the two lineages, which may provide insight into the dynamics of R. sanguineus s.l.-vectored diseases.