Date of Award
2025
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Biological and Environmental Sciences
Department
Biological Sciences
First Advisor
Jannelle Couret
Abstract
Ixodes scapularis, or the “black-legged tick,” are vectors for multiple human pathogens including the spirochete bacteria Borrelia burgdorferi (Bb), the etiological agent of Lyme Disease (LD) in humans. Given their small size and uniform appearance, standard methodology for studying I. scapularis behaviors in the field have been generally limited to aggregate measurements. This work aims to investigate the behavior of nymphal I. scapularis on a finer scale and quantify intrapopulation movement patterns in a field setting. Furthermore, we seek to explore behavioral phenotypic trait variation in association with Borrelia burgdorferi sensu stricto. Lastly, we seek to characterize intraspecific physiological variations in the respiratory metabolic patterns of nymphs.
The first chapter of this dissertation seeks to investigate the feasibility of quantifying individual movement patterns in a field setting. We constructed enclosures for fine-scale observation in the field. We then collected wild nymphal ticks and stored them in a high humidity environment to allow them to re-humidify. Nymphs were then individually marked with specific colors and placed into assigned arenas, alongside the same number of unmarked ticks. Location and behavior observations were taken twice a day to note where within the gridded system the nymph was located, and what type of behavior was being exhibited.
In the second chapter, we controlled for the life-history of the ticks, where we raised ticks from the egg stage into nymphs under controlled conditions. Half of the nymphs were exposed to Borrelia burgdorferi during their larval blood meal. Colors were assigned based on experimental treatment. Individual locations and behaviors were then tracked within field enclosures. Nymphs were then tested for Bb infection, allowing for the differentiation between three separate cohorts of ticks: those that had never been exposed to the bacteria (negative/control), ticks that were positive for the bacteria, and lastly, ticks that had been exposed to the bacteria but had not become infected with it (negative/exposed). Movement patterns could then be quantified and compared.
In the third chapter, we built custom 0.1mL chambers and ran flow-through respirometry to measure the CO2 outputs. CO2 bursts in ticks are associated with the opening of their spiracles for active gas exchange, however these openings are also directly associated with water loss, and therefore must be tightly regulated. Therefore, respiration patterns are directly correlated with desiccation and water balance and may be a mechanism that drives certain behaviors in varied conditions, such as moving below the leaf litter to rehydrate.
We found that behaviors varied amongst individual nymphs, which could be observed and quantified in the leaf litter through this marking method. We also found that horizontal movement patterns were more complex than could be measured through dispersal studies. We saw differences in survival, and that exposure without acquisition to Bb negatively impacted nymphal survival. We confirmed and measured discontinuous ventilation in nymphal I. scapularis, and also found intraspecific variation in multiple aspects of these cycles. This work shows the necessity of further research on finer scales to better understand the complex relationships between nymphs, their environments, and the mechanisms driving survival, behavior, and their role as a vector within their ecological systems.
Recommended Citation
Schofield, Samantha, "INTRAPOPULATION VARIATION IN THE BEHAVIOR AND PHYSIOLOGY OF NYMPHAL IXODES SCAPULARIS, AND POTENTIAL IMPACTS OF ASSOCIATION WITH BORRELIA BURGDORFERI SENSU STRICTO" (2025). Open Access Dissertations. Paper 4504.
https://digitalcommons.uri.edu/oa_diss/4504