Date of Award

Summer 8-22-2020

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Allison Gardner

Second Committee Member

Pauline Kamath

Third Committee Member

Danielle Levesque

Abstract

Lyme disease is the most common vector-borne disease in North America, and human cases have increased substantially over the past few decades. Blacklegged ticks (Ixodes scapularis) are the primary vector for Borrelia burgdorferi, the causative agent of Lyme disease. Understanding the significance of climate and other ecological drivers of blacklegged tick survival will aid in predicting future distributions of blacklegged tick populations and identifying areas that pose a risk of Lyme disease to humans. This research explored whether winter climate facilitates or inhibits the spread of blacklegged ticks and the pathogens they transmit. To determine the current range of blacklegged ticks in Maine, we systematically searched for and collected ticks across latitudinal and coastal-inland climate gradients across the state. We found higher densities of ticks in southern Maine (90.2 ticks/1000m2) than central Maine (17.8 ticks/1000m2) and no blacklegged ticks in northern Maine. To determine the effects of winter climate on blacklegged tick survival, we experimentally tested tick overwintering survival across the same gradients and assessed factors contributing to winter mortality both in locations where blacklegged tick populations are currently established and where the blacklegged tick remains undetected. Overwintering survival was not significantly different between sites in southern Maine compared to northern Maine, which was likely due to sufficient snowpack that protected against low ambient temperatures in northern Maine. Snow cover and leaf litter contributed significantly to overwintering survival at sites in both southern and northern Maine. Our results suggest that winter climate is not constraining blacklegged tick populations in areas north of their current range and that additional mechanisms may be limiting the expansion of ticks into northern Maine thus far. The results of this study will aid in understanding how climate factors contribute to blacklegged tick overwintering survival, which has important implications for tick abundance and distribution during the spring and summer. This information can be used to inform future studies to assess the effects of climate change on the distribution of blacklegged ticks and tick-borne pathogens.

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