THE MICROBIOME AND THE REPRODUCTIVE ECOLOGY OF Dermacentor variabilis AND Dermacentor andersoni IN WESTERN CANADA
Date
2024-07-22
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0002-9477-3033
Type
Thesis
Degree Level
Doctoral
Abstract
The geographical ranges of the Rocky Mountain wood tick, Dermacentor andersoni, and the American dog tick, Dermacentor variabilis, are largely allopatric on the Canadian prairies. Range expansion by D. variabilis to the north and west has resulted in an area of sympatry in south-western Saskatchewan, where both tick species experience similar environmental conditions. In this thesis, I examined the reproductive output, egg development, off-host survival of larvae, larval behaviour, and transovarial transmission of bacteria by D. andersoni and D. variabilis. I also compared the microbiomes of engorged females, their eggs and larvae of the two species using next generation sequencing and quantitative PCR assays. The results showed a strong correlation between the engorgement weight and the number of eggs laid by females. Dermacentor andersoni exhibited higher fecundity than D. variabilis. Egg development time and larval survival were significantly influenced by temperature and relative humidity. Eggs took less time to hatch at higher temperatures, with D. andersoni eggs developing faster rate than those of D. variabilis. Unfed larvae of both species had reduced survival at a low relative humidity, but D. andersoni were able to tolerate drier conditions than D. variabilis. Furthermore, a behavioral diapause was observed in D. variabilis larvae but not in D. andersoni. This indicated an adaptive strategy by D. variabilis to synchronize the life cycle with the onset of winter. A field experiment was also conducted to determine the survival of unfed D. variabilis larvae in field enclosures during which time they experienced sub-zero temperatures. Over 95% of larvae survived. The results of a second field experiment showed that leaf litter covered by snow is crucial for the overwinter survival of unfed D. variabilis larvae. The core microbiomes of D. variabilis females, eggs, and larvae were predominantly composed of Francisella-like endosymbionts (FLEs) and Rickettsia montanensis, whereas the core microbiomes of D. andersoni consisted of FLEs, Arsenophonus, Rickettsia peacockii and/or Rickettsia sp. 2. The presence of FLEs, R. montanensis, R. peacockii, Rickettsia sp. 2, and Arsenophonus in eggs and larvae is indicative of transovarial transmission by female ticks. The relative abundance of R. montanensis in unfed D. variabilis larvae exposed to fluctuating environmental conditions dramatically increased during the winter months. These findings for D. variabilis from recently established populations at the northern part of the species range, and for prairie and montane populations of D. andersoni, provides insight into what may limit their distributional ranges.
Description
Keywords
Tick survival, diapause, snow cover, cpn60, tick microbiome, surface sterilization, external microbiome, arthropod microbiome, endosymbionts, transovarial transmission
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Biology
Program
Biology