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. The temperate and tropical lineages overlap in range in some regions of the world, including the southwestern United States, where recent outbreaks of Rocky Mountain spotted fever are linked to R. sanguineus s.l. While it is unclear to what extent they may differ in their capacity to transmit pathogens, finer-scale resolution of temperate and tropical lineage distribution may provide insight into the ecology of these two tick groups and the epidemiology of R. sanguineus s.l.-vectored diseases. Using diagnostic polymerase chain reaction assays, we examined the geospatial trends in R. sanguineus s.l. lineages throughout Arizona. We found the temperate and tropical lineages were well delineated, with some overlap in the eastern part of the state. In one county, tropical and temperate ticks were collected on the same dog host, demonstrating that the two lineages are living in sympatry in some instances and may co-feed on the same host.

Nonpathogenic bacteria likely play important roles in the biology and vector competence of ticks and other arthropods. Coxiella, a gram-negative gammaproteobacterium, is one of the most commonly reported maternally inherited endosymbionts in ticks and has been associated with over 40 tick species. Species-specific Coxiella-like endosymbionts (CLEs) have been reported in the brown dog tick, Rhipicephalus sanguineus sensu lato (Acari: Ixodidae), throughout the world, while recent research suggests low Coxiella diversity among tick species. We investigated CLE diversity among R. sanguineus s.l. ticks across Arizona. We detected 37 recurrent sequence variants (SVs) of the symbiont, indicating greater diversity in these symbiotic bacteria than previously reported. However, two SVs accounted for the vast majority of 16S rRNA amplicon reads. These two dominant CLEs were both closely related to Candidatus C. mudrowiae, an identified symbiont of Rhipicephalus turanicus ticks. 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 mismatches between tick lineage and symbiont SV indicate that horizontal symbiont transfer may occur, perhaps via cofeeding of ticks from different lineages on the same dog. This study advances our understanding of CLE diversity in Rh. sanguineus s.l.