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Browsing Biology by Subject "American dog tick"
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Item Effect of snow cover on the off-host survival of Dermacentor variabilis (Acari: Ixodidae) larvae(Journal of Medical Entomology, 2024-01) Diyes, Chulantha P; Yunik, Matthew E M; Dergousoff, Shaun J; Chilton, NeilThe geographical range of the American dog tick, Dermacentor variabilis (Say), in Canada continues to expand northwards into areas with colder winter temperatures. Understanding what influences the off-host survival of D. variabilis over winter is important for predicting the northern distributional limit of this species. A field experiment was conducted to determine the effect of snow cover on the off-host survival of unfed D. variabilis larvae from a population situated near the northern distributional limit in Saskatchewan, Canada. Ticks were placed in tubes within 1 of 9 field enclosures (tickaria) in early fall. The 9 tickaria were divided into 3 equal treatment groups: no snow cover, natural snow cover (maximum depth of 25 cm) and extra snow cover (maximum depth of 32 cm). Tick survival was measured in mid-winter and in early spring (i.e., ~17 and ~26 wk after start of experiment). The results showed that snow cover had a significant impact on the relative humidity, but not temperature, in the tickaria. Larvae in tickaria with no snow cover had a higher mortality rate (27%) than larvae in tickaria with natural snow cover (6%) or extra snow cover (4%). Although snow cover enhanced off-host survival, many individuals were able to survive in sub-zero temperatures under leaf litter in the absence of continuous snow cover for a period of 108 days. These findings have implications for the construction of predictive models to determine the northern distributional limits of D. variabilis, a species that is an important vector of several pathogens.Item 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(Oxford University Press, 2025-04-17) Chilton, Neil B; Thampy, Prasobh R; Wolbaum, Cole R; Sterling, Emily E; Thoroughgood, Jessica T; Berg, Elisabeth D; Halpin, Alexander S; Diyes, Chulantha P; Yunik, Matthew E M; Díaz-Sánchez, Adrian A; Rochon, Kateryn; Lysyk, Timothy J; Dergousoff, Shaun JThe 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.