One tick closer to a better understanding of tick physiology and how to incorporate tick biology in a classroom

The black-legged tick, Ixodes scapularis (Acari: Ixodidae), transmits pathogens that can have detrimental effects on human and wildlife health. The pathogens that I. scapularis transmits include the causative agents of Lyme disease and Powassan virus disease. Due to various human impact factors such as global climate change, black-legged ticks have been expanding their range and establishing themselves in new areas, allowing them to encounter novel animal hosts as well as new diseases which could further impact human and wildlife health. While the ecology of the black-legged tick is well studied, its physiology is not, which may limit tick management success. This dissertation examines two important components of I. scapularis physiology: embryogenesis and host-seeking mechanisms. This dissertation also includes the development and examination of a high school-teaching unit focused on Ixodes scapularis and Lyme disease. Science education and the sharing of science to the general public is an important component of future tick management strategies. In Chapter 1, I provide background information about I. scapularis biology as well as give an overview of the Haller’s organ, which is the chemosensory structure found in ticks. In Chapter 2, I discuss a micro-computed tomography (MicroCT) scanning procedure I developed for examining the embryogenesis of the black-legged tick and document the full embryogenesis of I. scapularis. The development of the MicroCT scanning procedure consisted of a qualitative comparison of MicroCT scans of I. scapularis embryos at different development points using three different fixation methods. The scans at all three development points were compared to determine which of the fixation methods produced the most consistent images at the lowest cost. In this case, I found that using hot ethanol and dissolved iodine was the best method. I subsequently used this method to scan embryos every 24-hours starting from the time the eggs were laid until the ticks emerged as larvae. These scans revealed both internal and external development points throughout the embryogenesis such as when limbs form and when the Haller’s organ arises. This is the first documentation of I. scapularis embryogenesis and the third tick species to have its complete embryogenesis documented. In Chapter 3, I conducted a study aimed to identify the neurons associated with the black-legged tick’s Haller’s organ and what odors I. scapularis can detect using their Haller’s organ. Neuron identification was accomplished by puncturing sensilla within the Haller’s organ of female black-legged ticks and using the carbocyanine dye DiI to dye the neurons. Once the neurons were dyed they were visualized using fluorescent microscopy. Additionally, legs of female ticks were fixed and embedded in resin so that thin cross-sections of the leg could be observed using transmission electron microscopy. In order to determine what odors these ticks can detect, I attempted to use both an electrolegogram (ELG) and single-sensilla recordings (SSR) to obtain physiological recordings of neuron activity of the tick legs after exposure to various host odors. Although the ELG recordings were unsuccessful, the SSR recordings yielded recordings of the neuron activity of a single sensillum within the capsule aperture of the Haller’s organ. The odors that these ticks are able to detect were then used in a tick-choice behavioral assay in order to determine if ticks find these odors attractive or repulsive. These studies revealed key structures within the legs of I. scapularis which I suspect to be the neurons associated with the Haller’s organ. Additionally, I found that the large sensillum within the capsule aperture of the black-legged tick’s Haller’s organ is able to detect phenols. For the choice tests, of these phenols, I found that ticks exhibited repellent behavior when exposed to p-methylphenol, diluted at 10 µg/µL. In Chapter 4, I describe the development of a high school unit that is focused on I. scapularis and the spread of Lyme disease. The Lyme Disease unit development was guided by the Next Generation Science Standards (NGSS) and Framework, which Illinois recently adopted. The unit was presented to students in a way that included exposure to comics especially created to give instruction and introduce new material including the primary phenomenon of the unit: “Why are these kids getting sick and how can I stop the spread of the disease?”. After being presented with the phenomenon, students would act as scientists and use scientific data, extracted from published research that they analyzed to decide what line of questioning they wanted to follow. In addition to developing the unit, the unit was piloted by one teacher during three different school years. After each pilot trial, the unit was revised and student and teacher data were collected. These data were critically analyzed using qualitative and quantitative methods. Ultimately, the unit developed contained 16 lessons which encompassed 5 performance expectations, 9 practices, 5 Disciplinary Core Ideas, and 4 Cross-Cutting Concepts outlined in the NGSS and Framework. My analyses revealed that many of the revisions throughout the unit were beneficial to the unit and that overall students were able to successfully answer questions about tick biology, tick ecology, disease biology and human impact on disease biology. Additionally, students were able to develop models and apply their knowledge to new situations presented to them. Collectively, this dissertation addresses major gaps in tick physiology knowledge and demonstrates the importance of translating basic scientific research into truly educational teaching units.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste