WINTER AND MOLECULAR ECOLOGY OF THE AMERICAN DOG TICK, Dermacentor variabilis, ON THE CANADIAN PRAIRIES

The range of the American dog tick, Dermacentor variabilis, is expanding northwards into the Boreal transition ecoregion, where ticks experience colder winter temperatures. This thesis examined if adult ticks in a recently established population (Lizard Lake Community Pasture [LLCP]) near the edge of the species range survive over winter, have greater cold-hardiness than ticks in other populations, and if there are differences in the bacteria within in their microbiomes that may enhance overwinter survival. The results showed that the overwinter survivorship in outdoor enclosures was lower at LLCP than the established population at Sandy Hook. Also, significantly more females survived than males. Although the supercooling points (SCP = the temperature at which ticks freeze) of females did not differ from those of males, ticks from Sandy Hook had a colder SCP than ticks from LLCP, suggesting that adults at Sandy Hook are better adapted to deal with the environmental conditions they experience than those at LLCP. Also, the SCPs of lab-reared adults had a unimodal distribution, whereas those of questing adults in the field in early spring was bimodal, the later indicating the existence of two adult cohorts. By summer, there was a normal distribution of SCP values from questing ticks, suggesting a loss of some adults from the population. Therefore, environmental factors have an important impact on the SCP and off-host survival of ticks. Interestingly, bacteria present in the microbiomes of adults from LLCP during late summer were not different from adults that survived overwintering based on next-generation sequencing data. However, quantitative PCR analyses revealed that Francisella-like endosymbionts (FLEs), which are obligate tick mutualists, were more abundant in female ticks than males, especially for individuals that overwintered. Also, ticks infected with Rickettsia montanensis had a greater relative abundance of Rickettsia than FLEs, and a lower FLE abundance than ticks not infected R. montanensis, suggesting a negative interaction between these bacteria. The knowledge gained from this study has important implications for predicting range expansion by D. variabilis, and provides the foundation for future studies on the physiology and molecular ecology of the American dog tick.

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