Undergraduate Research in Biology: Ticks

Chair: Dr. Holly Gaff, Department of Biological Science

Preliminary Analysis of an Agent-Based Model for a Tick-Borne Disease

Ticks have a unique life history including a distinct set of life stages and a single blood meal per life stage. This makes tick-host interactions more complex from a mathematical perspective. In addition, any model of these interactions must involve a significant degree of stochasticity on the individual tick level. In an attempt to quantify these relationships, I have developed an individual-based model of the interactions between ticks and their hosts as well as the transmission of tick-borne disease between the two populations. The results from this model are compared with those from previously published differential equation based population models. The findings show that the agent-based model produces significantly lower prevalence of disease in both the ticks and their hosts than what is predicted by a similar differential equation model

Preprocessing data collected with the ACTS propagation terminal

Viewgraphs on preprocessing data collected with the ACTS propagation terminal are presented. The steps in ACTS data preprocessing are reviewed

Spatial heterogeneity in ecological models : two case studies

Two models are developed to explore the dynamics associated with spatial heterogeneity. The first model is the expansion of a single cell, fish population model to a landscape of interacting cells. The second model is a tick-borne disease model using a set of differential equations applied to a series of spatial patches. The spatially-explicit landscape fish population model (ALFISH) is a part of the Across Trophic Level System Simulation (ATLSS) project for the freshwater wetlands of the Everglades and Big Cypress Swamp. ALFISH was applied as part of the ATLSS project to Everglades restoration, one of the largest ecological restoration projects in the world. ALFISH has been improved to include new field information as that information became available. The only variable input into ALFISH is the hydrology. Up to 35% of variation in fish populations observed in field data corresponds to the variations predicted by ALFISH. The differential equations underlying the tick-borne disease model designed for the lone star tick (Amblyomma americanum) are analytically evaluated for one patch. The results show that under given criteria for the parameters, the system would be locally stable. For further study, the system is then solved numerically. Patches are identified as either grass or wooded and connected by migration. The disease is endemic in both patches unless some type of control is applied. If a control is applied, the disease is reduced to extremely low levels. If two patches, one grass and one wooded, are linked by migration, applying the control to the wooded patch is effective for controlling the disease while applying it in the grass patch is not. A final simulation using a twelve patch system is run to create results to compare with field data. The results show that the model produced qualitatively similar results to the field data which give reductions of 60% in tick density in the areas with control applied

Visualization of the Vortex Lattice Dynamics in Superfluid Helium

We study the lattice structure and dynamics of the quantized vortices in superfluid helium-4 using a new rotating experiment. This setup includes control of the entire apparatus from the rotating frame, installation of a new EMCCD camera that allows for imaging of nanoscale tracer particles, and the development and implementation of a new isolation cell, which permits investigation into new phenomena such as differential rotation in helium-II. We have observed the vortex lattice dynamics in the (r, &phi) plane (i.e. transverse to the vortices) and present here the first real-time visualization of Tkachenko waves in helium-II from this cross section. Additionally, we present evidence of differential rotation with distinct Stewartson layer boundaries, possible Kelvin-Helmholtz instabilities, and the formation and propagation of superfluid collective vortex eddies. We show that the angular velocity is a function of radius and may be driven by the geometry of the isolation cell. We also document the observation and analysis of gravity-capillary surface waves that demonstrate an interaction between the liquid helium free surface and the bulk of the fluid

Identifying Requirements for the Invasion of a Tick Species and Tick-Borne Pathogen Through TICKSIM

Ticks and tick-borne diseases have been on the move throughout the United State over the past twenty years. We use an agent-based model, TICKSIM, to identify the key parameters that determine the success of invasion of the tick and if that is successful, the success of the tick-borne pathogen. We find that if an area has competent hosts, an initial population of ten ticks is predicted to always establish a new population. The establishment of the tick-borne pathogen depends on three parameters: the initial prevalence in the ten founding ticks, the probability that a tick infects the longer-lived hosts and the probability that a tick infects the shorter lived hosts. These results indicate that the transmission rates to hosts in the newly established area can be used to predict the potential risk of disease to humans