Date of Award

Spring 5-2023

Document Type


Degree Name

Doctor of Philosophy (PhD)


Biological Sciences


Ecological Sciences

Committee Director

Holly D. Gaff

Committee Director

David T. Gauthier

Committee Member

Wayne Hynes

Committee Member

Andrea Varela-Stokes

Committee Member

Tom Allen


Connectivity among populations helps to maintain genetic diversity, population stability, and resilience. The Gulf Coast tick, Amblyomma maculatum, is a vector of the pathogen Rickettsia parkeri. Persistence of tick populations with high rates of R. parkeri infection poses health risks to humans and animals. Mitochondrial haplotypes were characterized by sequencing a fragment of the mitochondrial 16S rRNA gene. A comparative study of A. maculatum and Amblyomma americanum was conducted to identify similar and unique patterns between the species within the same region. Next, I compared A. maculatum sites across three different regions of the United States. This work examined diversity and connectivity between and among A. maculatum populations to resolve questions about the process of range expansion and population establishment. The first research aim was to characterize the genetic diversity within A. maculatum populations and infer connectivity among populations. These population genetics comparisons revealed that Gulf Coast tick populations showed signs of isolation compared to A. americanum populations, which have higher gene flow. One A. maculatum population was dominated by an otherwise rare haplotype, an unusual pattern that signaled a possible founder effect from a long-distance drop-off. Given the apparent isolation and unusual dominance within one unique population, a landscape analysis was completed by examining remote-sensing data to determine correlations between environmental variables and A. maculatum populations for the purpose of identifying suitable and unsuitable habitat that could influence patterns of movement and barriers to gene flow. None of the environmental variables had clear correlations with A. maculatum population presence, so barriers could not be identified. Finally, an agent-based model was created to simulate recurrent introductions of Gulf Coast ticks in rasterized models of several field study sites. Propagule pressure was positively associated with haplotype richness, whereas edge patches had a negative effect on richness. The simulation results suggested that limited immigration as well as landscape configurations could explain rare patterns of low diversity.


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