Genetic diversity and phylogeographic relationships of Dermacentor variabilis (Acari: Ixodidae) within an established population in southern Manitoba (Canada), and the prevalence of Rickettsia montanensis and Francisella-like endosymbionts.

Abstract

The primary objective of this study was to determine if DNA sequences of the mitochondrial (mt) cytochrome oxidase c subunit 1 gene (cox1) and/or the mt 16S ribosomal RNA (rRNA) gene can be used to study the population genetics and phylogeography of the American dog tick, Dermacentor variabilis (Say). DNA sequences were determined for 200 adult ticks collected from an established population in a region of Manitoba (Canada) where there have been recent outbreaks of bovine anaplasmosis. Given this, a secondary objective was to test these ticks for the presence of Anaplasma marginale Theiler and 2 other bacterial pathogens, Rickettsia rickettsii Brumpt and Francisella tularensis (McCoy and Chapin 1912) Dorofe'ev 1947. However, no ticks were PCR-positive for these bacteria, whereas 15% of ticks were PCR-positive for R. montanensis Weiss and Moulder and 96% contained Francisella-like endosymbionts. Nucleotide and haplotype diversity among ticks was greater for cox1 than the 16S rRNA gene, thus cox1 is more useful for examining the genetic diversity within and among D. variabilis populations. The 33 cox1 haplotypes could be separated into 3 haplogroups, but when combined with sequence data from GenBank, 6 clades were evident, 2 of which comprised ticks from primarily Saskatchewan, Manitoba, western Ontario, South Dakota, and Wisconsin. These findings indicate that cox1 can be used to understand the phylogeography of D. variabilis, but more sequences are needed from individuals in other populations across geographical range of this tick species, particularly those on the Canadian prairies where D. variabilis is undergoing range expansion.